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  • 1.
    Adamus-Gorka, Magdalena
    et al.
    Stockholm University, Faculty of Science, Medical Radiation Physics (together with KI).
    Mavroidis, Panayiotis
    Stockholm University, Faculty of Science, Medical Radiation Physics (together with KI).
    Brahme, Anders
    Stockholm University, Faculty of Science, Medical Radiation Physics (together with KI).
    Lind, Bengt K
    Stockholm University, Faculty of Science, Medical Radiation Physics (together with KI).
    An “Effective functional subunit size” model for the dose response of rat spinal cord paralysis2007In: 13th International Congress of Radiation Research, San Fransisco, USA, July 8-12, 2007, 2007Conference paper (Other (popular science, discussion, etc.))
    Abstract [en]

    Background: Radiobiological models for normal tissue complication probability (NTCP) are more and more commonly used in order to estimate the clinical outcome of radiation therapy. A normal tissue complication probability model to be considered a good and reliable one should fulfill the following two requirements: (a) it should predict the sigmoid shape of the dose-response curve as well as possible and (b) it should duly handle the volume effect. In the work from 2005 (IJROBP 61(3):892-900, 2005) P. van Luijk et al. suggest that none of the existing NTCP models is able to describe the volume effects present in the rat spinal cord during irradiation with small proton beams and they indicate the need for developing such new models.

    Methods: We have used the experimental data from H. Bijl et al. (IJROBP 52(1):205-211, 2002) to try explaining the change in the fifty percent effective dose (ED50) for different field sizes. We initiated this study to evaluate whether the induction of white matter necrosis in rat spinal cord after irradiation with small proton beams could be explained independent of used NTCP model. We therefore introduced a new concept of effective FSU dose, where a convolution of the original dose distribution with a function describing the effective size of a single FSU results in the average doses in a functional subunit. Such procedure allows determining the ED50 in an FSU of a certain size, within the irradiation field. We have also looked at non uniform dose distributions to see whether using a similar method we can explain the so called “bath and shower experiments” (IJROBP 57(1): 274-281, 2003).

    Results: Using the least square method to compare the effective doses for different sizes of functional subunits with the experimental data we observe the best fit for about 8 mm length. It seems that this length could be understood as an effective size of functional subunits in rat spinal cord, explaining what is otherwise interpreted as a volume effect. For the non uniform dose distributions an effective FSU length of 5 mm gives the optimal fit with the Probit dose-response model.

    Conclusions: The concept of an effective FSU length seems to explain at least part of the effects seen when small portions of the rat spinal cord are irradiated. The most likely FSU length for the shower and bath experiments is 5 mm according to these calculations.

  • 2. Ainsbury, E A
    et al.
    Bakhanova, E
    Barquinero, J F
    Brai, M
    Chumak, V
    Correcher, V
    Darroudi, F
    Fattibene, P
    Gruel, G
    Guclu, I
    Horn, S
    Jaworska, A
    Kulka, U
    Lindholm, C
    Lloyd, D
    Longo, A
    Marrale, M
    Monteiro Gil, O
    Oestreicher, U
    Pajic, J
    Rakic, B
    Romm, H
    Trompier, F
    Veronese, I
    Voisin, P
    Vral, A
    Whitehouse, C A
    Wieser, A
    Woda, C
    Wojcik, Andrzej
    Stockholm University, Faculty of Science, Department of Genetics, Microbiology and Toxicology.
    Rothkamm, K
    REVIEW OF RETROSPECTIVE DOSIMETRY TECHNIQUES FOR EXTERNAL IONISING RADIATION EXPOSURES.2011In: Radiation Protection Dosimetry, ISSN 0144-8420, E-ISSN 1742-3406, Vol. 147, no 4, 573-592 p.Article in journal (Refereed)
    Abstract [en]

    The current focus on networking and mutual assistance in the management of radiation accidents or incidents has demonstrated the importance of a joined-up approach in physical and biological dosimetry. To this end, the European Radiation Dosimetry Working Group 10 on 'Retrospective Dosimetry' has been set up by individuals from a wide range of disciplines across Europe. Here, established and emerging dosimetry methods are reviewed, which can be used immediately and retrospectively following external ionising radiation exposure. Endpoints and assays include dicentrics, translocations, premature chromosome condensation, micronuclei, somatic mutations, gene expression, electron paramagnetic resonance, thermoluminescence, optically stimulated luminescence, neutron activation, haematology, protein biomarkers and analytical dose reconstruction. Individual characteristics of these techniques, their limitations and potential for further development are reviewed, and their usefulness in specific exposure scenarios is discussed. Whilst no single technique fulfils the criteria of an ideal dosemeter, an integrated approach using multiple techniques tailored to the exposure scenario can cover most requirements.

  • 3. Ainsbury, Elizabeth A.
    et al.
    Higueras, Manuel
    Puig, Pedro
    Einbeck, Jochen
    Samaga, Daniel
    Francesc Barquinero, Joan
    Barrios, Lleonard
    Brzozowska, Beata
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute. University of Warsaw, Poland.
    Fattibene, Paola
    Gregoire, Eric
    Jaworska, Alicja
    Lloyd, David
    Oestreicher, Ursula
    Romm, Horst
    Rothkamm, Kai
    Roy, Laurence
    Sommer, Sylwester
    Terzoudi, Georgia
    Thierens, Hubert
    Trompier, Francois
    Vral, Anne
    Woda, Clemens
    Uncertainty of fast biological radiation dose assessment for emergency response scenarios2017In: International Journal of Radiation Biology, ISSN 0955-3002, E-ISSN 1362-3095, Vol. 93, no 1, 127-135 p.Article in journal (Refereed)
    Abstract [en]

    Purpose: Reliable dose estimation is an important factor in appropriate dosimetric triage categorization of exposed individuals to support radiation emergency response. Materials and methods: Following work done under the EU FP7 MULTIBIODOSE and RENEB projects, formal methods for defining uncertainties on biological dose estimates are compared using simulated and real data from recent exercises. Results: The results demonstrate that a Bayesian method of uncertainty assessment is the most appropriate, even in the absence of detailed prior information. The relative accuracy and relevance of techniques for calculating uncertainty and combining assay results to produce single dose and uncertainty estimates is further discussed. Conclusions: Finally, it is demonstrated that whatever uncertainty estimation method is employed, ignoring the uncertainty on fast dose assessments can have an important impact on rapid biodosimetric categorization.

  • 4. Ainsbury, Elizabeth
    et al.
    Badie, Christophe
    Barnard, Stephen
    Manning, Grainne
    Moquet, Jayne
    Abend, Michael
    Antunes, Ana Catarina
    Barrios, Lleonard
    Bassinet, Celine
    Beinke, Christina
    Bortolin, Emanuela
    Bossin, Lily
    Bricknell, Clare
    Brzoska, Kamil
    Buraczewska, Iwona
    Huertas Castano, Carlos
    Cemusova, Zina
    Christiansson, Maria
    Mateos Cordero, Santiago
    Coster, Guillaume
    Della Monac, Sara
    Desangles, Francois
    Discher, Michael
    Dominguez, Inmaculada
    Doucha-Senf, Sven
    Eakins, Jon
    Fattibene, Paola
    Filippi, Silvia
    Frenzel, Monika
    Georgieva, Dimka
    Gregoire, Eric
    Guogyte, Kamile
    Hadjidekova, Valeria
    Hadjiiska, Ljubomira
    Hristova, Rositsa
    Karakosta, Maria
    Kis, Eniko
    Kriehuber, Ralf
    Lee, Jungil
    Lloyd, David
    Lumniczky, Katalin
    Lyng, Fiona
    Macaeva, Ellina
    Majewski, Matthaeus
    Vanda Martins, S.
    McKeever, Stephen W. S.
    Meade, Aidan
    Medipally, Dinesh
    Meschini, Roberta
    M'kacher, Radhia
    Gil, Octavia Monteiro
    Montero, Alegria
    Moreno, Mercedes
    Noditi, Mihaela
    Oestreicher, Ursula
    Oskamp, Dominik
    Palitti, Fabrizio
    Palma, Valentina
    Pantelias, Gabriel
    Pateux, Jerome
    Patrono, Clarice
    Pepe, Gaetano
    Port, Matthias
    Jesus Prieto, Maria
    Quattrini, Maria Cristina
    Quintens, Roel
    Ricoul, Michelle
    Roy, Laurence
    Sabatier, Laure
    Sebastia, Natividad
    Sholom, Sergey
    Sommer, Sylwester
    Staynova, Albena
    Strunz, Sonja
    Terzoudi, Georgia
    Testa, Antonella
    Trompier, Francois
    Valente, Marco
    Van Hoey, Olivier
    Veronese, Ivan
    Wojcik, Andrzej
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Woda, Clemens
    Integration of new biological and physical retrospective dosimetry methods into EU emergency response plans - joint RENEB and EURADOS inter-laboratory comparisons2017In: International Journal of Radiation Biology, ISSN 0955-3002, E-ISSN 1362-3095, Vol. 93, no 1, 99-109 p.Article in journal (Refereed)
    Abstract [en]

    Purpose: RENEB, 'Realising the European Network of Biodosimetry and Physical Retrospective Dosimetry,' is a network for research and emergency response mutual assistance in biodosimetry within the EU. Within this extremely active network, a number of new dosimetry methods have recently been proposed or developed. There is a requirement to test and/or validate these candidate techniques and inter-comparison exercises are a well-established method for such validation. Materials and methods: The authors present details of inter-comparisons of four such new methods: dicentric chromosome analysis including telomere and centromere staining; the gene expression assay carried out in whole blood; Raman spectroscopy on blood lymphocytes, and detection of radiation induced thermoluminescent signals in glass screens taken from mobile phones. Results: In general the results show good agreement between the laboratories and methods within the expected levels of uncertainty, and thus demonstrate that there is a lot of potential for each of the candidate techniques. Conclusions: Further work is required before the new methods can be included within the suite of reliable dosimetry methods for use by RENEB partners and others in routine and emergency response scenarios.

  • 5.
    Alevronta, Eleftheria
    et al.
    Stockholm University, Faculty of Science, Medical Radiation Physics (together with KI).
    Ahlberg, Alexander
    Mavroidis, Panayiotis
    Stockholm University, Faculty of Science, Medical Radiation Physics (together with KI).
    al-Abany, Massoud
    Friesland, Signe
    Tilikidis, Aris
    Laurell, Goran
    Lind, Bengt K.
    Stockholm University, Faculty of Science, Medical Radiation Physics (together with KI).
    Dose-response relations for stricture in the proximal oesophagus from head and neck radiotherapy2010In: Radiotherapy and Oncology, ISSN 0167-8140, E-ISSN 1879-0887, Vol. 97, no 1, 54-59 p.Article in journal (Refereed)
    Abstract [en]

    Background and purpose: Determination of the dose-response relations for oesophageal stricture after radiotherapy of the head and neck. Material and methods: In this study 33 patients who developed oesophageal stricture and 39 patients as controls are included. The patients received radiation therapy for head and neck cancer at Karolinska University Hospital, Stockholm, Sweden. For each patient the 3D dose distribution delivered to the upper 5 cm of the oesophagus was analysed. The analysis was conducted for two periods, 1992-2000 and 2001-2005, due to the different irradiation techniques used. The fitting has been done using the relative seriality model. Results: For the treatment period 1992-2005, the mean doses were 49.8 and 33.4 Gy, respectively, for the cases and the controls. For the period 1992-2000, the mean doses for the cases and the controls were 49.9 and 45.9 Gy and for the period 2001-2005 were 49.8 and 21.4 Gy. For the period 2001-2005 the best estimates of the dose-response parameters are D-50 = 61.5 Gy (52.9-84.9 Gy), gamma = 1.4 (0.8-2.6) and s = 0.1 (0.01-0.3). Conclusions: Radiation-induced strictures were found to have a dose response relation and volume dependence (low relative seriality) for the treatment period 2001-2005. However, no dose response relation was found for the complete material.

  • 6. Andreassen, Björn
    et al.
    Holmberg, Rickard
    Brahme, Anders
    Janek Strååt, Sara
    Stockholm University, Faculty of Science, Medical Radiation Physics (together with KI). Stockholm University, Faculty of Science, Department of Physics.
    PET/CT measurements and GEANT4 simulations of the inducedpositron activity from high energy scanned photon beamsManuscript (preprint) (Other academic)
  • 7.
    Andreassen, Björn
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Strååt, Sara Janek
    Stockholm University, Faculty of Science, Department of Physics.
    Holmberg, Rickard
    Stockholm University, Faculty of Science, Department of Physics.
    Näfstadius, Peder
    Brahme, Anders
    Stockholm University, Faculty of Science, Department of Physics.
    Fast IMRT with narrow high energy scanned photon beams2011In: Medical physics (Lancaster), ISSN 0094-2405, Vol. 38, no 8, 4774-4784 p.Article in journal (Refereed)
    Abstract [en]

    Purpose: Since the first publications on intensity modulated radiation therapy (IMRT) in the early 1980s almost all efforts have been focused on fairly time consuming dynamic or segmental multileaf collimation. With narrow fast scanned photon beams, the flexibility and accuracy in beam shaping increases, not least in combination with fast penumbra trimming multileaf collimators. Previously, experiments have been performed with full range targets, generating a broad bremsstrahlung beam, in combination with multileaf collimators or material compensators. In the present publication, the first measurements with fast narrow high energy (50 MV) scanned photon beams are presented indicating an interesting performance increase even though some of the hardware used were suboptimal. Methods: Inverse therapy planning was used to calculate optimal scanning patterns to generate dose distributions with interesting properties for fast IMRT. To fully utilize the dose distributional advantages with scanned beams, it is necessary to use narrow high energy beams from a thin bremsstrahlung target and a powerful purging magnet capable of deflecting the transmitted electron beam away from the generated photons onto a dedicated electron collector. During the present measurements the scanning system, purging magnet, and electron collimator in the treatment head of the MM50 racetrack accelerator was used with 3-6 mm thick bremsstrahlung targets of beryllium. The dose distributions were measured with diodes in water and with EDR2 film in PMMA. Monte Carlo simulations with GEANT4 were used to study the influence of the electrons transmitted through the target on the photon pencil beam kernel. Results: The full width at half-maximum (FWHM) of the scanned photon beam was 34 mm measured at isocenter, below 9.5 cm of water, 1 m from the 3 mm Be bremsstrahlung target. To generate a homogeneous dose distribution in a 10 x 10 cm(2) field, the authors used a spot matrix of 100 equal intensity beam spots resulting in a uniformity of collimated 80%-20% penumbra of 9 mm at a primary electron energy of 50 MeV. For the more complex cardioid shaped dose distribution, they used 270 spots, which at a pulse repetition frequency of 200 Hz is completed every 1.36 s. Conclusions: The present measurements indicate that the use of narrow scanned photon beams is a flexible and fast method to deliver advanced intensity modulated beams. Fast scanned photon IMRT should, therefore, be a very interesting modality in the delivery of biologically optimized radiation therapy with the possibility for in vivo treatment verification with PET-CT imaging.

  • 8.
    Andreo, Pedro
    Stockholm University, Faculty of Science, Department of Physics. Karolinska Institutet, Sweden.
    Dose to 'water-like' media or dose to tissue in MV photons radiotherapy treatment planning: still a matter of debate2015In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 60, no 1, 309-337 p.Article in journal (Refereed)
    Abstract [en]

    The difference between Monte Carlo Treatment Planning (MCTP) based on the assumption of 'water-like' tissues with densities obtained from CT procedures, or on tissue compositions derived from CT-determined densities, have been investigated. Stopping powers and electron fluences have been calculated for a range of media and body tissues for 6 MV photon beams, including changes in their physical data (density and stopping powers). These quantities have been used to determine absorbed doses using cavity theory. It is emphasized that tissue compositions given in ICRU or ICRP reports should not be given the standing of physical constants as they correspond to average values obtained for a limited number of human-body samples. It has been shown that mass stopping-power ratios to water are more dependent on patient-to-patient composition differences, and therefore on their mean excitation energies (I-values), than on mass density. Electron fluence in different media are also more dependent on media composition (and their I-values) than on density. However, as a consequence of the balance between fluence and stopping powers, doses calculated from their product are more constant than what the independent stopping powers and fluence variations suggest. Additionally, cancelations in dose ratios minimize the differences between the 'water-like' and 'tissue' approaches, yielding practically identical results except for bone, and to a lesser extent for adipose tissue. A priori, changing from one approach to another does not seem to be justified considering the large number of approximations and uncertainties involved throughout the treatment planning tissue segmentation and dose calculation procedures. The key issue continues to be the composition of tissues and their I-values, and as these cannot be obtained for individual patients, whatever approach is selected does not lead to significant differences from a water reference dose, the maximum of these being of the order of 5% for bone tissues. Considering, however, current developments in advanced dose calculation methods, planning in terms of dose-to-tissue should be the preferred choice, under the expectancy that progress in the field will gradually improve some of the crude approximations included in MCTP and numerical transport methods. The small differences obtained also show that a retrospective conversion from dose-to-tissue to dose-to-water, based on a widely used approach, would mostly increase the final uncertainty of the treatment planning process. It is demonstrated that, due to the difference between electron fluence distributions in water and in body tissues, the conversion requires an additional fluence correction that has so far been neglected. An improved expression for the conversion and data for the fluence correction factor are provided. These will be necessary even in a dose-to-tissue environment, for the normalization of the treatment plan to the reference dosimetry of the treatment unit, always calibrated in terms of absorbed dose to water.

  • 9.
    Andreo, Pedro
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Wulff, Joerg
    Burns, David T.
    Palmans, Hugo
    Consistency in reference radiotherapy dosimetry: resolution of an apparent conundrum when Co-60 is the reference quality for charged-particle and photon beams2013In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 58, no 19, 6593-6621 p.Article in journal (Refereed)
    Abstract [en]

    Substantial changes in ion chamber perturbation correction factors in Co-60 gamma-rays, suggested by recent Monte Carlo (MC) calculations, would cause a decrease of about 1.5% in the reference dosimetry of all types of charged particles (electrons, protons and heavier ions) based on calculated k(Q) values. It has gone largely unnoticed that the ratio of calibration coefficients N-D,N-w,N-Co60 and N-K,N-air,N-Co60 yields an experimental value of F-ch,F-Co60 = (s(w-air) pch)(Co60) through N-D,N-air,N-Co60. Coefficients provided by the IAEA and traceable to the BIPM for 91 NE-2571 chambers result in an average F-ch,F-Co60 which is compared with published (and new) MC simulations and with the value in IAEA TRS-398. It is shown that TRS-398 agrees within 0.12% with the experimental F-ch,F-Co60. The 1.5% difference resulting from MC calculations (1.1% for the new simulations) cannot be justified using current fundamental data and BIPM standards if consistency in the entire dosimetry chain is sought. For photons, MC k(Q) factors are compared with TRS-398. Using the same uncertainty for W-air, the two sets of data overlap considerably. Experimental k(Q) values from standards laboratories lie between the two sets of calculated values, showing no preference for one set over the other. Observed chamber-to-chamber differences, that include the effect of waterproof sleeves (also seen for Co-60), justify the recommendation in TRS-398 for k(Q) values specifically measured for the user chamber. Current developments on I-values for the stopping powers of water and graphite are presented. A weighted average I-water = 78 +/- 2 eV is obtained from published experimental and DRF-based values; this would decrease sw-air for all types of radiotherapy beams between 0.3% and 0.6%, and would consequently decrease the MC derived F-ch,F-Co60. The implications of a recent proposal for I-graphite = 81 eV are analysed, resulting in a potential decrease of 0.7% in N-K,N-air,N-Co60 which would raise the experimental F-ch,F-Co60; this would result in an increase of about 0.8% in the current TRS-398 value when referred to the BIPM standards. MC derived F-ch,F-Co60 using new stopping powers would then agree at a level of 0.1% with the experimental value, confirming the need for consistency in the dosimetry chain data. Should world average standards be used as reference, the figures would become +0.4% for TRS-398 and -0.3% for the MC calculation. F-ch,F-Q calculated for megavoltage photons using new stopping powers would decrease by between 0.2% and 0.5%. When they enter as a ratios in k(Q), differences with MC values based on current key data would be within 0.2% but their discrepancy with k(Q) experimental photon values remains unresolved. For protons the new data would require an increase in W-air,W-Q of about 0.6%, as this is inferred from a combination of calorimetry and ionometry. This consistent scenario would leave unchanged the current TRS-398 k(Q) (NE-2571) data for protons, as well as for ions heavier than protons unless new independent W-air,W-Q values become available. Also in these advanced radiotherapy modalities, the need for maintaining data consistency in an analysis that unavoidably must include the complete dosimetry chain is demonstrated.

  • 10.
    Andræ, Nils
    Stockholm University, Faculty of Science, Medical Radiation Physics (together with KI).
    Commissioning and validation of small subfields in Step-and-shoot IMRT2008Independent thesis Basic level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    One of the most used irradiation techniques in modern radiation therapy is step-and-shoot IMRT. The accuracy of this technique when delivering complex dose distributions strongly depends on the size of the subfields. The aims of this study is to determine the minimum size of subfields that can be used efficiently in Step-and-Shoot IMRT, to investigate the validation process for beam delivery and treatment planning dose calculations, and to find recommendations for practical clinical implementations.

    Two different detectors, a CC04 ion chamber and a SFD stereotactic diode, have been used for measuring head scatter factors in air (Sc), total output factors (Scp) and dose profiles in water for a wide range of field sizes. The measurements were compared to calculations done with a pre-release version of the Nucletron MasterPlanTM v 3.1 treatment planning system that employs a novel, high resolution fluence modelling for both its pencil beam and collapsed cone dose calculation algorithms. Collimator settings were explicitly checked using FWHM film measurements with a build-up sheet of tungsten placed close to the treatment head to reduce the influence from lateral electron transport and geometrical penumbra. An analysis of the influence and sensitivity of Scp for small fields with respect to the linear accelerator source size and shape was also made.

    The measurements with the ionization chamber and the stereotactic diode showed good agreements with each other and with the treatment planning system calculations for field sizes larger than 2×2 cm2. For small field sizes, measurements with different detectors yielded different results. Calculations showed agreements with measurements with the smallest detector, provided careful field size calibration and commissioning of calculation parameters. Uncertainties in collimator settings and source characteristics were shown to yield large uncertainties in Scp for fields smaller than 2×2 cm2.

    The treatment planning system was found to properly handle small subfields but results were very sensitive to uncertainties in source size, as well as calibration and reproducibility of the collimator settings. Therefore if subfields smaller than 2×2 cm2 are to be used in IMRT extra care should be taken to determine the source characteristics and to calibrate the collimators. The volume of the detectors used for validation of such small fields and the loss of charged particle equilibrium conditions also have to be taken into consideration.

  • 11.
    Antonovic, Laura
    Stockholm University, Faculty of Science, Medical Radiation Physics (together with KI).
    Evaluation of the lithium formate EPR dosimetry system for dose measurements around 192Ir brachytherapy sources2008Independent thesis Basic level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The dose distribution around brachytherapy (BT) sources is characterized by steep dose gradients and an energy spectrum varying rapidly with depth in water around the source. These two properties make experimental verification of the dose distribution difficult, and put high demands on the dosimetry system in use regarding precision, size and energy dependence. The American Association of Physicists in Medicine (AAPM) recommends lithium fluoride (LiF) thermo-luminescence dosimetry (TLD) to be used for verification measurements, as it is the only dosimetry system meeting the requirements, but still the total combined uncertainty in dose-rate determination is as high as 7-9 % (1 σ). Lithium formate is a new dosimetry material that is less energy dependent than LiF, but more sensitive than the most common EPR (electron paramagnetic resonance) dosimetry material, alanine. In order to evaluate lithium formate EPR for BT dosimetry, dosimeters were produced for experimental dose determination around BT source 192Ir. The dosimeters were calibrated against an ionization chamber in a high energy photon beam. Dose to water was determined at 1, 3 and 5 cm radial distance from the source, which was stepped along a straight line in a PMMA phantom. The experiments were performed twice using 4 dosimeters per distance and experiment. Methods to correct for energy dependence were developed and evaluated. The uncertainty in measured dose was estimated. The experimental dose values agreed with the values from the treatment planning system with a maximum deviation of 3.3 %, and an average 1 σ uncertainty of 3 % at 3 and 5 cm and 5 % at 1cm. Uncertainty in radial distance from the source as well as source calibration were the dominating contributions to the total combined uncertainty. Lithium formate EPR has been shown to be a promising alternative to LiF TLD for BT dosimetry.

  • 12.
    Bajinskis, Ainars
    et al.
    Stockholm University, Faculty of Science, Department of Genetics, Microbiology and Toxicology.
    Lindegren, Helene
    Stockholm University, Faculty of Science, Department of Neurochemistry.
    Johansson, Lotta
    Stockholm University, Faculty of Science, Department of Neurochemistry.
    Harms-Ringdahl, Mats
    Stockholm University, Faculty of Science, Department of Genetics, Microbiology and Toxicology.
    Forsby, Anna
    Stockholm University, Faculty of Science, Department of Neurochemistry.
    Low-Dose/Dose-Rate gamma Radiation Depresses Neural Differentiation and Alters Protein Expression Profiles in Neuroblastoma SH-SY5Y Cells and C17.2 Neural Stem Cells2011In: Radiation Research, ISSN 0033-7587, Vol. 175, no 2, 185-192 p.Article in journal (Refereed)
    Abstract [en]

    The effects of low doses of ionizing radiation on cellular development in the nervous system are presently unclear. The focus of the present study was to examine low-dose gamma-radiation-induced effects on the differentiation of neuronal cells and on the development of neural stem cells to glial cells. Human neuroblastoma SH-SY5Y cells were exposed to (137)Cs gamma rays at different stages of retinoic acid-induced neuronal differentiation, and neurite formation was determined 6 days after exposure. When SH-SY5Y cells were exposed to low-dose-rate gamma rays at the onset of differentiation, the number of neurites formed per cell was significantly less after exposure to either 10, 30 or 100 mGy compared to control cells. Exposure to 10 and 30 mGy attenuated differentiation of immature C17.2 mouse-derived neural stem cells to glial cells, as verified by the diminished expression of glial fibrillary acidic protein. Proteomic analysis of the neuroblastoma cells by 2D-PAGE after 30 mGy irradiation showed that proteins involved in neuronal development were downregulated. Proteins involved in cell cycle and proliferation were altered in both cell lines after exposure to 30 mGy; however, the rate of cell proliferation was not affected in the low-dose range. The radiation-induced attenuation of differentiation and the persistent changes in protein expression is indicative of an epigenetic rather than a cytotoxic mechanism. (C) 2011 by Radiation Research Society

  • 13. Barbeiro, A. R.
    et al.
    Ureba, Ana
    Stockholm University, Faculty of Science, Department of Physics. Universidad de Sevilla, Spain; Instituto de Biomedicina de Sevilla, IBIS, Spain; Karolinska Institutet, Sweden.
    Baeza, J. A.
    Linares, R.
    Perucha, M.
    Jimenez-Ortega, E.
    Velazquez, S.
    Mateos, J. C.
    Leal, A.
    3D VMAT Verification Based on Monte Carlo Log File Simulation with Experimental Feedback from Film Dosimetry2016In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 11, no 11, e0166767Article in journal (Refereed)
    Abstract [en]

    A model based on a specific phantom, called QuAArC, has been designed for the evaluation of planning and verification systems of complex radiotherapy treatments, such as volumetric modulated arc therapy (VMAT). This model uses the high accuracy provided by the Monte Carlo (MC) simulation of log files and allows the experimental feedback from the high spatial resolution of films hosted in QuAArC. This cylindrical phantom was specifically designed to host films rolled at different radial distances able to take into account the entrance fluence and the 3D dose distribution. Ionization chamber measurements are also included in the feedback process for absolute dose considerations. In this way, automated MC simulation of treatment log files is implemented to calculate the actual delivery geometries, while the monitor units are experimentally adjusted to reconstruct the dose-volume histogram (DVH) on the patient CT. Prostate and head and neck clinical cases, previously planned with Monaco and Pinnacle treatment planning systems and verified with two different commercial systems (Delta4 and COMPASS), were selected in order to test operational feasibility of the proposed model. The proper operation of the feedback procedure was proved through the achieved high agreement between reconstructed dose distributions and the film measurements (global gamma passing rates > 90% for the 2%/2 mm criteria). The necessary discretization level of the log file for dose calculation and the potential mismatching between calculated control points and detection grid in the verification process were discussed. Besides the effect of dose calculation accuracy of the analytic algorithm implemented in treatment planning systems for a dynamic technique, it was discussed the importance of the detection density level and its location in VMAT specific phantom to obtain a more reliable DVH in the patient CT. The proposed model also showed enough robustness and efficiency to be considered as a pre-treatment VMAT verification system.

  • 14.
    Bauer, Florian
    Stockholm University, Faculty of Science, Department of Physics.
    Detector Considerations for Time-of-Flight in Positron Emission Tomography2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Positron-Emission-Tomography (PET) is a modern imaging technique in nuclear medicine providing quantitative 3D distribution of a radioactive tracer substance in the human body. The gamma-detector is the first link in the chain of components that constitutes a PET. It converts incoming radiation into optical light pulses, which are detected by photo multiplier tubes. Here the light is converted into electric pulses, to be further processed by the acquisition electronics. Improving detector sensitivity and resolution is of great value in research and in clinical practice.

    The focus of this work is to improve the detector to give it time-of-flight (TOF) capabilities, in order to further improve sensitivity, which in turn leads to increased image quality, faster scan time and/or reduced dose exposure for the patient.

    Image quality has improved over the years, but losses in image quality have been reported for heavy patients, due to increased attenuation, and more dispersed counts over a larger volume. Instrumentation limits are still significant in heavy patient images, but the incorporation of TOF information promises to alleviate some of the limitations.

    In order to improve the timing resolution of the detector fast photo-multipliers and a novel scheme to extract the event timing trigger from a detector by using the summed dynode signal were investigated.

    When designing new PET detectors, it is important to have detailed understanding and control of the light sharing mechanisms in the crystal arrays. Therefore it was necessary to perform optical simulations and single crystal light output measurements to derive a model for an LSO block detector.

    Another way to improve the image quality is to use the depth-of-interaction (DOI) of the gamma ray within the detector. It is shown that a multi-layer phoswich detector comprised of LSO with different decay times and TOF capability, combines the benefits of TOF and DOI in one detector, maximizing the effective sensitivity gain.

  • 15.
    Bellander, Martin
    et al.
    Stockholm University, Faculty of Social Sciences, Aging Research Center (ARC), (together with KI).
    Berggren, Rasmus
    Stockholm University, Faculty of Social Sciences, Aging Research Center (ARC), (together with KI).
    Mårtensson, Johan
    Brehmer, Yvonne
    Stockholm University, Faculty of Social Sciences, Aging Research Center (ARC), (together with KI). Max Planck Institute for Human Development, Germany.
    Wenger, Elisabeth
    Li, Tie-Qiang
    Bodammer, Nils C.
    Shing, Yee-Lee
    Werkle-Bergner, Markus
    Lövdén, Martin
    Stockholm University, Faculty of Social Sciences, Aging Research Center (ARC), (together with KI).
    Behavioral correlates of changes in hippocampal gray matter structure during acquisition of foreign vocabulary2016In: NeuroImage, ISSN 1053-8119, E-ISSN 1095-9572, Vol. 131, 205-213 p.Article in journal (Refereed)
    Abstract [en]

    Experience can affect human gray matter volume. The behavioral correlates of individual differences in such brain changes are not well understood. In a group of Swedish individuals studying Italian as a foreign language, we investigated associations among time spent studying, acquired vocabulary, baseline performance on memory tasks, and gray matter changes. As a way of studying episodic memory training, the language learning focused on acquiring foreign vocabulary and lasted for 10 weeks. T-1-weighted structural magnetic resonance imaging and cognitive testing were performed before and after the studies. Learning behavior was monitored via participants' use of a smartphone application dedicated to the study of vocabulary. A whole-brain analysis showed larger changes in gray matter structure of the right hippocampus in the experimental group (N = 33) compared to an active control group (N = 23). A first path analyses revealed that time spent studying rather than acquired knowledge significantly predicted change in gray matter structure. However, this association was not significant when adding performance on baseline memory measures into the model, instead only the participants' performance on a short-term memory task with highly similar distractors predicted the change. This measure may tap similar individual difference factors as those involved in gray matter plasticity of the hippocampus.

  • 16.
    Beltran-Pardo, Eliana
    et al.
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Jonsson, K. Ingemar
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute. Kristianstad University, Sweden.
    Harms-Ringdahl, Mats
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Haghdoost, Siamak
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Wojcik, Andrzej
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Tolerance to Gamma Radiation in the Tardigrade Hypsibius dujardini from Embryo to Adult Correlate Inversely with Cellular Proliferation2015In: PLoS ONE, ISSN 1932-6203, Vol. 10, no 7, e0133658Article in journal (Refereed)
    Abstract [en]

    Tardigrades are highly tolerant to desiccation and ionizing radiation but the mechanisms of this tolerance are not well understood. In this paper, we report studies on dose responses of adults and eggs of the tardigrade Hypsibius dujardini exposed to gamma radiation. In adults the LD50/48h for survival was estimated at similar to 4200 Gy, and doses higher than 100 Gy reduced both fertility and hatchability of laid eggs drastically. We also evaluated the effect of radiation (doses 50 Gy, 200 Gy, 500 Gy) on eggs in the early and late embryonic stage of development, and observed a reduced hatchability in the early stage, while no effect was found in the late stage of development. Survival of juveniles from irradiated eggs was highly affected by a 500 Gy dose, both in the early and the late stage. Juveniles hatched from eggs irradiated at 50 Gy and 200 Gy developed into adults and produced offspring, but their fertility was reduced compared to the controls. Finally we measured the effect of low temperature during irradiation at 4000 Gy and 4500 Gy on survival in adult tardigrades, and observed a slight delay in the expressed mortality when tardigrades were irradiated on ice. Since H. dujardini is a freshwater tardigrade with lower tolerance to desiccation compared to limno-terrestrial tardigrades, the high radiation tolerance in adults, similar to limno-terrestrial tardigrades, is unexpected and seems to challenge the idea that desiccation and radiation tolerance rely on the same molecular mechanisms. We suggest that the higher radiation tolerance in adults and late stage embryos of H. dujardini (and in other studied tardigrades) compared to early stage embryos may partly be due to limited mitotic activity, since tardigrades have a low degree of somatic cell division (eutely), and dividing cells are known to be more sensitive to radiation.

  • 17.
    Bengtsson, Emil
    Stockholm University, Faculty of Science, Medical Radiation Physics (together with KI).
    Doseplanning ocular tumors with 125I-seeds2006Independent thesis Basic level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Since 1986 patients with ocular malignant melanoma have been treated with Ru-106 plaques at S:t Erik Eye Hospital. In 1998 I-125 radioactive seed plaques was presented as an alternative to Ru-106 when treating tumors with an apical height greater than 7 mm. Until June 2005 the doseplanning of these plaques was based on a depth-dose curve made in the dose planning system Cadplan supplied by Varian Medical Systems. In the recent years the capabilities of computerized 3D dose planning system has increased greatly. The number of types of seeds on the market has also increased.

    In order to implement the modern 3D dose planning system Brachy Vision 7.3.10 in planning the I-125 plaques, a review of the dose planning process have been done.

    The ultra sound equipment used by the ophthalmologist to determine the apical height of the tumor has been investigated in terms of accuracy. A phantom has been developed for this task.

    As new seeds entered the market a comparision have been made comparing the Amersham 6711 seed with the Bebig I25.S06 seed. A method for measuring the activity of the single seeds has also been developed.

    The dose planning system Brachy Vision 7.3.10 have been compared to the old dose planning method, and an implementation of the plaques into Brachy Vision have been made.

    The ultra sound equipment was accurate in the regions of interest. It was also discovered that the Bebig I25.S06 seed gave slightly higher dose compared to the Amersham 6711 with the same activity. The difference between the seeds is however small. The results indicate that the old dose planning method gave a slight underdosage.

  • 18.
    Benmakhlouf, Hamza
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Karolinska Institutet, Sweden.
    Sempau, Josep
    Andreo, Pedro
    Stockholm University, Faculty of Science, Department of Physics. Karolinska Institutet, Sweden.
    Output correction factors for nine small field detectors in 6 MV radiation therapy photon beams: A PENELOPE Monte Carlo study2014In: Medical physics (Lancaster), ISSN 0094-2405, Vol. 41, no 4, 041711- p.Article in journal (Refereed)
    Abstract [en]

    Purpose: To determine detector-specific output correction factors, k(Qclin,Qmsr)(fclin,fmsr) in 6 MV small photon beams for air and liquid ionization chambers, silicon diodes, and diamond detectors from two manufacturers. Methods: Field output factors, defined according to the international formalism published by Alfonso et al. [Med. Phys. 35, 5179-5186 (2008)], relate the dosimetry of small photon beams to that of the machine-specific reference field; they include a correction to measured ratios of detector readings, conventionally used as output factors in broad beams. Output correction factors were calculated with the PENELOPE Monte Carlo (MC) system with a statistical uncertainty (type-A) of 0.15% or lower. The geometries of the detectors were coded using blueprints provided by the manufacturers, and phase-space files for field sizes between 0.5 x 0.5 cm(2) and 10 x 10 cm(2) from a Varian Clinac iX 6 MV linac used as sources. The output correction factors were determined scoring the absorbed dose within a detector and to a small water volume in the absence of the detector, both at a depth of 10 cm, for each small field and for the reference beam of 10 x 10 cm(2). Results: The Monte Carlo calculated output correction factors for the liquid ionization chamber and the diamond detector were within about +/- 1% of unity even for the smallest field sizes. Corrections were found to be significant for small air ionization chambers due to their cavity dimensions, as expected. The correction factors for silicon diodes varied with the detector type (shielded or un-shielded), confirming the findings by other authors; different corrections for the detectors from the two manufacturers were obtained. The differences in the calculated factors for the various detectors were analyzed thoroughly and whenever possible the results were compared to published data, often calculated for different accelerators and using the EGSnrc MC system. The differences were used to estimate a type-B uncertainty for the correction factors. Together with the type-A uncertainty from the Monte Carlo calculations, an estimation of the combined standard uncertainty was made, assigned to the mean correction factors from various estimates. Conclusions: The present work provides a consistent and specific set of data for the output correction factors of a broad set of detectors in a Varian Clinac iX 6 MV accelerator and contributes to improving the understanding of the physics of small photon beams. The correction factors cannot in general be neglected for any detector and, as expected, their magnitude increases with decreasing field size. Due to the reduced number of clinical accelerator types currently available, it is suggested that detector output correction factors be given specifically for linac models and field sizes, rather than for a beam quality specifier that necessarily varies with the accelerator type and field size due to the different electron spot dimensions and photon collimation systems used by each accelerator model. (C) 2014 American Association of Physicists in Medicine.

  • 19.
    Brehmer, Yvonne
    et al.
    Stockholm University, Faculty of Social Sciences, Aging Research Center (ARC), (together with KI). Max Planck Institute for Human Development, Germany.
    Shing, Yee Lee
    Heekeren, Hauke R.
    Lindenberger, Ulman
    Bäckman, Lars
    Stockholm University, Faculty of Social Sciences, Aging Research Center (ARC), (together with KI).
    Training-induced changes in subsequent-memory effects: No major differences among children, younger adults, and older adults2016In: NeuroImage, ISSN 1053-8119, E-ISSN 1095-9572, Vol. 131, 214-225 p.Article in journal (Refereed)
    Abstract [en]

    The neural correlates of encoding mode, or the state of forming new memory episodes, have been found to change with age and mnemonic training. However, it is unclear whether neural correlates of encoding success, termed subsequent-memory (SM) effects, also differ by age and mnemonic skill. In a multi-session training study, we investigated whether SM effects are altered by instruction and training in a mnemonic skill, and whether such alterations differ among children, younger adults, and older adults. Before and after strategy training, fMRI data were collected while participants were memorizing word pairs. In all age groups, participants receiving training showed greater performance gains than control group participants. Analysis of task-relevant regions showed training-induced reductions in SM effects in left frontal regions. Reductions in SM effects largely generalized across age and primarily reflected greater training-induced activation increases for omissions than for remembered items, indicating that training resulted in more consistent use of the mnemonic strategy. The present results reveal no major age differences in SM effects in children, younger adults, and older adults.

  • 20.
    Brzozowska, Beata
    et al.
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute. University of Warsaw, Poland.
    Ainsbury, Elizabeth
    Baert, Annelot
    Beaton-Green, Lindsay
    Barrios, Leonardo
    Francesc Barquinero, Joan
    Bassinet, Celine
    Beinke, Christina
    Benedek, Anett
    Beukes, Philip
    Bortolin, Emanuela
    Buraczewska, Iwona
    Burbidge, Christopher
    De Amicis, Andrea
    De Angelis, Cinzia
    Della Monaca, Sara
    Depuydt, Julie
    De Sanctis, Stefania
    Dobos, Katalin
    Domene, Mercedes Moreno
    Dominguez, Inmaculada
    Facco, Eva
    Fattibene, Paola
    Frenzel, Monika
    Gil, Octavia Monteiro
    Gonon, Geraldine
    Gregoire, Eric
    Gruel, Gaetan
    Hadjidekova, Valeria
    Hatzi, Vasiliki I.
    Hristova, Rositsa
    Jaworska, Alicja
    Kis, Eniko
    Kowalska, Maria
    Kulka, Ulrike
    Lista, Florigio
    Lumniczky, Katalin
    Martinez-Lopez, Wilner
    Meschini, Roberta
    Moertl, Simone
    Moquet, Jayne
    Noditi, Mihaela
    Oestreicher, Ursula
    Orta Vazquez, Manuel Luis
    Palma, Valentina
    Pantelias, Gabriel
    Montoro Pastor, Alegria
    Patrono, Clarice
    Piqueret-Stephan, Laure
    Quattrini, Maria Cristina
    Regalbuto, Elisa
    Ricoul, Michelle
    Roch-Lefevre, Sandrine
    Roy, Laurence
    Sabatier, Laure
    Sarchiapone, Lucia
    Sebastia, Natividad
    Sommer, Sylwester
    Sun, Mingzhu
    Suto, Yumiko
    Terzoudi, Georgia
    Trompier, Francois
    Vral, Anne
    Wilkins, Ruth
    Zafiropoulos, Demetre
    Wieser, Albrecht
    Woda, Clemens
    Wojcik, Andrzej
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute. Jan Kochanowski University, Poland.
    RENEB accident simulation exercise2017In: International Journal of Radiation Biology, ISSN 0955-3002, E-ISSN 1362-3095, Vol. 93, no 1, 75-80 p.Article in journal (Refereed)
    Abstract [en]

    Purpose: The RENEB accident exercise was carried out in order to train the RENEB participants in coordinating and managing potentially large data sets that would be generated in case of a major radiological event. Materials and methods: Each participant was offered the possibility to activate the network by sending an alerting email about a simulated radiation emergency. The same participant had to collect, compile and report capacity, triage categorization and exposure scenario results obtained from all other participants. The exercise was performed over 27 weeks and involved the network consisting of 28 institutes: 21 RENEB members, four candidates and three non-RENEB partners. Results: The duration of a single exercise never exceeded 10 days, while the response from the assisting laboratories never came later than within half a day. During each week of the exercise, around 4500 samples were reported by all service laboratories (SL) to be examined and 54 scenarios were coherently estimated by all laboratories (the standard deviation from the mean of all SL answers for a given scenario category and a set of data was not larger than 3 patient codes). Conclusions: Each participant received training in both the role of a reference laboratory (activating the network) and of a service laboratory (responding to an activation request). The procedures in the case of radiological event were successfully established and tested.

  • 21.
    Böhlen, Till Tobias
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Karolinska Institutet.
    Bauer, J.
    Dosanjh, M.
    Ferrari, A.
    Haberer, T.
    Parodi, K.
    Patera, V.
    Mairani, A.
    A Monte Carlo-based treatment-planning tool for ion beam therapy2013In: Journal of radiation research, ISSN 0449-3060, E-ISSN 1349-9157, Vol. 54, 77-81 p.Article in journal (Refereed)
    Abstract [en]

    Ion beam therapy, as an emerging radiation therapy modality, requires continuous efforts to develop and improve tools for patient treatment planning (TP) and research applications. Dose and fluence computation algorithms using the Monte Carlo (MC) technique have served for decades as reference tools for accurate dose computations for radiotherapy. In this work, a novel MC-based treatment-planning (MCTP) tool for ion beam therapy using the pencil beam scanning technique is presented. It allows single-field and simultaneous multiple-fields optimization for realistic patient treatment conditions and for dosimetric quality assurance for irradiation conditions at state-of-the-art ion beam therapy facilities. It employs iterative procedures that allow for the optimization of absorbed dose and relative biological effectiveness (RBE)-weighted dose using radiobiological input tables generated by external RBE models. Using a re-implementation of the local effect model (LEM), the MCTP tool is able to perform TP studies using ions with atomic numbers Z < 8. Example treatment plans created with the MCTP tool are presented for carbon ions in comparison with a certified analytical treatment-planning system. Furthermore, the usage of the tool to compute and optimize mixed-ion treatment plans, i.e. plans including pencil beams of ions with different atomic numbers, is demonstrated. The tool is aimed for future use in research applications and to support treatment planning at ion beam facilities.

  • 22.
    Böhlen, Till Tobias
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Dosanjh, M.
    Ferrari, A.
    Gudowska, Irena
    Stockholm University, Faculty of Science, Department of Physics.
    Mairani, A.
    FLUKA simulations of the response of tissue-equivalent proportional counters to ion beams for applications in hadron therapy and space2011In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 56, no 20, 6545-6561 p.Article in journal (Refereed)
    Abstract [en]

    For both cancer therapy with protons and ions (hadron therapy) and space radiation environments, the spatial energy deposition patterns of the radiation fields are of importance for quantifying the resulting radiation damage in biological structures. Tissue-equivalent proportional counters (TEPC) are the principal instruments for measuring imparted energy on a microscopic scale and for characterizing energy deposition patterns of radiation. Moreover, the distribution of imparted energy can serve as a complementary quantity to particle fluences of the primary beam and secondary fragments for characterizing a radiation field on a physical basis for radiobiological models. In this work, the Monte Carlo particle transport code FLUKA is used for simulating energy depositions in TEPC by ion beams. The capability of FLUKA in predicting imparted energy and derived quantities, such as lineal energy, for microscopic volumes is evaluated by comparing it with a large set of TEPC measurements for different ion beams with atomic numbers ranging from 1 to 26 and energies from 80 up to 1000 MeV/n. The influence of different physics configurations in the simulation is also discussed. It is demonstrated that FLUKA can simulate energy deposition patterns of ions in TEPC cavities accurately and that it provides an adequate description of the main features of the spectra.

  • 23. Champion, C.
    et al.
    Incerti, S.
    Perrot, Y.
    Delorme, R.
    Bordage, M. C.
    Bardies, M.
    Mascialino, Barbara
    Stockholm University, Faculty of Science, Department of Physics.
    Tran, H. N.
    Ivanchenko, V.
    Bernal, M.
    Francis, Z.
    Groetz, J. -E
    Fromm, M.
    Campos, L.
    Dose point kernels in liquid water: An intra-comparison between GEANT4-DNA and a variety of Monte Carlo codes2014In: Applied Radiation and Isotopes, ISSN 0969-8043, E-ISSN 1872-9800, Vol. 83, 137-141 p.Article in journal (Refereed)
    Abstract [en]

    Modeling the radio-induced effects in biological medium still requires accurate physics models to describe the interactions induced by all the charged particles present in the irradiated medium in detail. These interactions include inelastic as well as elastic processes. To check the accuracy of the very low energy models recently implemented into the GEANT4 toolkit for modeling the electron slowing-down in liquid water, the simulation of electron dose point kernels remains the preferential test. In this context, we here report normalized radial dose profiles, for mono-energetic point sources, computed in liquid water by using the very low energy GEANT4-DNA physics processes available in the GEANT4 toolkit. In the present study, we report an extensive intra-comparison of profiles obtained by a large selection of existing and well-documented Monte-Carlo codes, namely, EGSnrc, PENELOPE, CPA100, FLUKA and MCNPX.

  • 24. Chiotis, Konstantinos
    et al.
    Saint-Aubert, Laure
    Savitcheva, Irina
    Jelic, Vesna
    Andersen, Pia
    Jonasson, My
    Eriksson, Jonas
    Lubberink, Mark
    Almkvist, Ove
    Stockholm University, Faculty of Social Sciences, Department of Psychology, Biological psychology. Karolinska Institutet, Sweden; Karolinska University Hospital, Sweden.
    Wall, Anders
    Antoni, Gunnar
    Nordberg, Agneta
    Imaging in-vivo tau pathology in Alzheimer's disease with THK5317 PET in a multimodal paradigm2016In: European Journal of Nuclear Medicine and Molecular Imaging, ISSN 1619-7070, E-ISSN 1619-7089, Vol. 43, no 9, 1686-1699 p.Article in journal (Refereed)
    Abstract [en]

    Purpose The aim of this study was to explore the cerebral distribution of the tau-specific PET tracer [F-18]THK5317 (also known as (S)-[F-18]THK5117) retention in different stages of Alzheimer's disease; and study any associations with markers of hypometabolism and amyloid-beta deposition. Methods Thirty-three individuals were enrolled, including nine patients with Alzheimer's disease dementia, thirteen with mild cognitive impairment (MCI), two with non-Alzheimer's disease dementia, and nine healthy controls (five young and four elderly). In a multi-tracer PET design [F-18]THK5317, [C-11] Pittsburgh compound B ([C-11]PIB), and [F-18]FDG were used to assess tau pathology, amyloid-beta deposition and cerebral glucose metabolism, respectively. The MCI patients were further divided into MCI [C-11]PIB-positive (n=11) and MCI [C-11]PIB-negative (n=2) groups. Results Test-retest variability for [F-18]THK5317-PET was very low (1.17-3.81 %), as shown by retesting five patients. The patients with prodromal (MCI [C-11]PIB-positive) and dementia-stage Alzheimer's disease had significantly higher [F-18]THK5317 retention than healthy controls (p=0.002 and p=0.001, respectively) in areas exceeding limbic regions, and their discrimination from this control group (using the area under the curve) was >98 %. Focal negative correlations between [F-18]THK5317 retention and [F-18]FDG uptake were observed mainly in the frontal cortex, and focal positive correlations were found between [F-18]THK5317 and [C-11] PIB retentions isocortically. One patient with corticobasal degeneration syndrome and one with progressive supranuclear palsy showed no [C-11]PIB but high [F-18]THK5317 retentions with a different regional distribution from that in Alzheimer's disease patients. Conclusions The tau-specific PET tracer [F-18]THK5317 images in vivo the expected regional distribution of tau pathology. This distribution contrasts with the different patterns of hypometabolism and amyloid-beta deposition.

  • 25. Conti, Maurizio
    et al.
    Eriksson, Lars
    Stockholm University, Faculty of Science, Department of Physics. Karolinska Institute, Sweden; Siemens Healthcare Molecular Imaging, USA; University of Tennessee, USA.
    Physics of pure and non-pure positron emitters for PET: a review and a discussion2016In: EJNMMI Physics, ISSN 2197-7364, Vol. 3, no 1, 8Article, review/survey (Refereed)
    Abstract [en]

    With the increased interest in new PET tracers, gene-targeted therapy, immunoPET, and theranostics, other radioisotopes will be increasingly used in clinical PET scanners, in addition to F-18. Some of the most interesting radioisotopes with prospective use in the new fields are not pure short-range beta(+) emitters but can be associated with gamma emissions in coincidence with the annihilation radiation (prompt gamma), gamma-gamma cascades, intense Bremsstrahlung radiation, high-energy positrons that may escape out of the patient skin, and high-energy gamma rays that result in some e(+)/e(-) pair production. The high level of sophistication in data correction and excellent quantitative accuracy that has been reached for F-18 in recent years can be questioned by these effects. In this work, we review the physics and the scientific literature and evaluate the effect of these additional phenomena on the PET data for each of a series of radioisotopes: C-11, N-13, O-15, F-18, Cu-64, Ga-68, Br-76, Rb-82, Y-86, Zr-89, Y-90, and I-124. In particular, we discuss the present complications arising from the prompt gammas, and we review the scientific literature on prompt gamma correction. For some of the radioisotopes considered in this work, prompt gamma correction is definitely needed to assure acceptable image quality, and several approaches have been proposed in recent years. Bremsstrahlung photons and Lu-176 background were also evaluated.

  • 26. Conti, Maurizio
    et al.
    Eriksson, Lars
    Stockholm University, Faculty of Science, Department of Physics. Siemens Healthcare Molecular Imaging, USA; Karolinska Institute, Sweden; University of Tennessee, USA.
    Rothfuss, Harold
    Sjoeholm, Therese
    Townsend, David
    Rosenqvist, Göran
    Carlier, Thomas
    Characterization of Lu-176 background in LSO-based PET scanners2017In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 62, no 9, 3700-3711 p.Article in journal (Refereed)
    Abstract [en]

    LSO and LYSO are today the most common scintillators used in positron emission tomography. Lutetium contains traces of Lu-176, a radioactive isotope that decays beta(-) with a cascade of. photons in coincidence. Therefore, Lutetium-based scintillators are characterized by a small natural radiation background. In this paper, we investigate and characterize the Lu-176 radiation background via experiments performed on LSO-based PET scanners. LSO background was measured at different energy windows and different time coincidence windows, and by using shields to alter the original spectrum. The effect of radiation background in particularly count-starved applications, such as Y-90 imaging, is analysed and discussed. Depending on the size of the PET scanner, between 500 and 1000 total random counts per second and between 3 and 5 total true coincidences per second were measured in standard coincidence mode. The LSO background counts in a Siemens mCT in the standard PET energy and time windows are in general negligible in terms of trues, and are comparable to that measured in a BGO scanner of similar size.

  • 27.
    Costa Ferreira, Brigida
    Stockholm University, Faculty of Science, Medical Radiation Physics (together with KI).
    Biological optimization of angle of incidence and intensity modulation in breast and cervix cancer radiation therapy2004Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Biological treatment optimization aim at improving radiation therapy by accounting for the radiobiological tumour and normal tissues response properties when optimizing the dose delivery. Generally traditional methods, using only dosimetrical measures, disregard the nonlinear radiation response of different tumours and normal tissues. The accumulated knowledge on tissue response to radiation, in the form of more accurate dose response relations, cell survival models and their associated biological parameters, alongside with the tools for biological treatment plan optimization, has allowed the present investigation on the potential merits of biologically based treatment optimization in radiation therapy.

    With a more widespread implementation of intensity modulated radiation therapy in the clinic, there is an increasing demand for faster and safer treatment delivery techniques. In this thesis biological treatment plan optimization, using the probability to achieve complication free tumour control as the quantifier for treatment outcome, was applied to radiation therapy of early breast cancer and advanced cervix cancer. It is shown that very conformal dose distributions can generally be produced with 3 or 4 optimally orientated coplanar intensity modulated beams, without having clinically significant losses in treatment outcome from the optimal dose distribution.

    By using exhaustive search methods, the optimal coplanar beam directions for intensity modulated photon beams for early breast cancer and the optimal non-coplanar directions for an advanced cervix cancer were investigated. Although time consuming, exhaustive search methods have the advantage of revealing most features involving interactions between a small number of beams and how this may influence the treatment outcome. Thus phase spaces may serve as a general database for selecting an almost optimal treatment configuration for similar patients. Previous knowledge acquired with physically optimized uniform beam radiation therapy may not apply when intensity modulated biological optimization is used. Thus unconventional treatment directions were sometimes found.

  • 28.
    Dasu, Alexandru
    et al.
    Norrland University Hospital, Sweden.
    Toma-Dasu, Iuliana
    Stockholm University, Faculty of Science, Medical Radiation Physics (together with KI). Karolinska Insitutet, Sweden.
    What is the clinically relevant relative biologic effectiveness? A warning for fractionated treatments with high linear energy transfer radiation2008In: International Journal of Radiation Oncology, Biology, Physics, ISSN 0360-3016, Vol. 70, no 3, 867-874 p.Article in journal (Refereed)
    Abstract [en]

    PURPOSE: To study the clinically relevant relative biologic effectiveness (RBE) of fractionated treatments with high linear energy transfer (LET) radiation and to identify the important factors that might influence the transfer of tolerance and curative levels from low LET radiation. These are important questions in the light of the growing interest for the therapeutic use of radiation with higher LET than electrons or photons. METHODS AND MATERIALS: The RBE of various fractionated schedules was analyzed with theoretical models for radiation effect, and the resulting predictions were compared with the published clinical and experimental data regarding fractionated irradiation with high LET radiation. RESULTS: The clinically relevant RBE increased for greater doses per fraction, in contrast to the predictions from single-dose experiments. Furthermore, the RBE for late-reacting tissues appeared to modify more quickly than that for early-reacting tissues. These aspects have quite important clinical implications, because the increased biologic effectiveness reported for this type of radiation would otherwise support the use of hypofractionation. Thus, the differential between acute and late-reacting tissues could put the late-reacting normal tissues at more risk from high LET irradiation; however, at the same time, it could increase the therapeutic window for slow-growing tumors. CONCLUSIONS: The modification of the RBE with the dose per fraction must be carefully taken into consideration when devising fractionated treatments with high LET radiation. Neglecting to do so might result in an avalanche of complications that could obscure the potential advantages of the therapeutic use of this type of radiation.

  • 29.
    De Luelmo, Sandro Carlos
    Stockholm University, Faculty of Science, Medical Radiation Physics (together with KI).
    Characterization of the 60Co therapy unit Siemens Gammatron 1 using BEAMnrc Monte Carlo simulations2006Independent thesis Basic level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The aim of this work is to characterize the beam of the 60Co therapy unit “Siemens Gammatron 1”, used at the Swedish Radiation Protection Authority (SSI) to calibrate therapy level ionization chambers. SSI wants to know the spectra in the laboratory’s reference points and a verified, virtual model of the 60Co unit to be able to compare current and future experiments to Monte Carlo simulations.

    EGSnrc is a code for performing Monte Carlo simulations. By using BEAMnrc, which is an additional package that simplifies the building process of a geometry in the EGS-code, the whole Gammatron at SSI was defined virtually. In this work virtual models for two experimental setups were built: the Gammatron irradiating in air to simulate the air-kerma calibration geometry and the Gammatron irradiating a water phantom similar to that used for the absorbed dose to water calibrations.

    The simulations are divided into two different substeps: one for the fixed part of the Gammatron and one for the variable part to be able to study different entities and to shorten simulation times.

    The virtual geometries are verified by comparing Monte Carlo results with measurements. When it was verified that the virtual geometries were to be trusted, they were used to generate the Gammatron photon spectra in air and water with different field sizes and at different depths. The contributions to the photon spectra from different regions in the Gammatron were also collected. This is something that is easy to achieve with Monte Carlo calculations, but difficult to obtain with ordinary detectors in real life measurements.

    The results from this work give SSI knowledge of the photon spectra in their reference points for calibrations in air and in water phantom. The first step of the virtual model (fixed part of Gammatron) can be used for future experimental setups at SSI.

  • 30. Depuydt, Julie
    et al.
    Baeyens, Ans
    Barnard, Stephen
    Beinke, Christina
    Benedek, Anett
    Beukes, Philip
    Buraczewska, Iwona
    Darroudi, Firouz
    De Sanctis, Stefania
    Domingue, Inmaculada
    Gil, Octavia Monteiro
    Hadjidekova, Valeria
    Kis, Eniko
    Kulka, Ulrike
    Lista, Florigio
    Lumniczky, Katalin
    M'kacher, Radhia
    Moquet, Jayne
    Obreja, Doina
    Oestreicher, Ursula
    Pajic, Jelena
    Pastor, Nuria
    Popova, Ljubomira
    Regalbuto, Elisa
    Ricoul, Michelle
    Sabatier, Laure
    Slabbert, Jacobus
    Sommer, Sylwester
    Testa, Antonella
    Thierens, Hubert
    Wojcik, Andrzej
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Vral, Anne
    RENEB intercomparison exercises analyzing micronuclei (Cytokinesis-block Micronucleus Assay)2017In: International Journal of Radiation Biology, ISSN 0955-3002, E-ISSN 1362-3095, Vol. 93, no 1, 36-47 p.Article in journal (Refereed)
    Abstract [en]

    Purpose: In the framework of the 'Realizing the European Network of Biodosimetry' (RENEB) project, two intercomparison exercises were conducted to assess the suitability of an optimized version of the cytokinesis-block micronucleus assay, and to evaluate the capacity of a large laboratory network performing biodosimetry for radiation emergency triages. Twelve European institutions participated in the first exercise, and four non-RENEB labs were added in the second one. Materials and methods: Irradiated blood samples were shipped to participating labs, whose task was to culture these samples and provide a blind dose estimate. Micronucleus analysis was performed by automated, semi-automated and manual procedures. Results: The dose estimates provided by network laboratories were in good agreement with true administered doses. The most accurate estimates were reported for low dose points (<= 0.94 Gy). For higher dose points (>= 2.7 Gy) a larger variation in estimates was observed, though in the second exercise the number of acceptable estimates increased satisfactorily. Higher accuracy was achieved with the semi-automated method. Conclusion: The results of the two exercises performed by our network demonstrate that the micronucleus assay is a useful tool for large-scale radiation emergencies, and can be successfully implemented within a large network of laboratories.

  • 31.
    Djordjevic, Milos
    Stockholm University, Faculty of Science, Medical Radiation Physics (together with KI).
    Evaluation of Geometric Accuracy and Image Quality of an On-Board Imager (OBI)2007Independent thesis Basic level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In this project several tests were performed to evaluate the performance of an On-Board Imager® (OBI) mounted on a clinical linear accelerator. The measurements were divided into three parts; geometric accuracy, image registration and couch shift accuracy, and image quality. A cube phantom containing a radiation opaque marker was used to study the agreement with treatment isocenter for both kV-images and cone-beam CT (CBCT) images. The long term stability was investigated by acquiring frontal and lateral kV images twice a week over a 3 month period. Stability in vertical and longitudinal robotic arm motion as well as the stability of the center-of-rotation was evaluated. Further, the agreement of kV image and CBCT center with MV image center was examined.

    A marker seed phantom was used to evaluate and compare the three applications in image registration; 2D/2D, 2D/3D and 3D/3D. Image registration using kV-kV image sets were compared with MV MV and MV-kV image sets. Further, the accuracy in 2D/2D matches with images acquired at non-orthogonal gantry angles was evaluated. The image quality in CBCT images was evaluated using a Catphan® phantom. Hounsfield unit (HU) uniformity and linearity was compared with planning CT. HU accuracy is crucial for dose verification using CBCT data.

    The geometric measurements showed good long term stability and accurate position reproducibility after robotic arm motions. A systematic error of about 1 mm in lateral direction of the kV-image center was detected. A small difference between kV and CBCT center was observed and related to a lateral kV detector offset. The vector disagreement between kV- and MV-image centers was  2 mm at some gantry angles. Image registration with the different match applications worked sufficiently. 2D/3D match was seen to correct more accurately than 2D/2D match for large translational and rotational shifts. CBCT images acquired with full-fan mode showed good HU uniformity but half fan images were less uniform. In the soft tissue region the HU agreement with planning CT was reasonable while a larger disagreement was observed at higher densities. This work shows that the OBI is robust and stable in its performance. With regular QC and calibrations the geometric precision of the OBI can be maintained within 1 mm of treatment isocenter.

  • 32. Dzintars, Erik
    et al.
    Papanikolaou, Nikos
    Mavroidis, Panayiotis
    Stockholm University, Faculty of Science, Department of Physics. Karolinska Institute, Sweden.
    Sadeghi, Amir
    Stathakis, Sotirios
    Application of an independent dose calculation software for estimating the impact of inter-fractional setup shifts in Helical Tomotherapy treatments2013In: Physica medica (Testo stampato), ISSN 1120-1797, E-ISSN 1724-191X, Vol. 29, no 6, 615-623 p.Article in journal (Refereed)
    Abstract [en]

    The purpose of this study is to validate the capability of in-house independent point dose calculation software to be used as a second check for Helical Tomotherapy treatment plans. The software performed its calculations in homogenous conditions (using the Cheese phantom, which is a cylindrical phantom with radius 15 cm and length 18 cm) using a factor-based algorithm. Fifty patients, who were treated for pelvic (10), prostate (14), lung (10), head 82 neck (12) and brain (4) cancers, were used. Based on the individual patient kVCT images and the pretreatment MVCT images for each treatment fraction, the corresponding daily patient setup shifts in the IEC-X, IEC-Y, and IEC-Z directions were registered. For each patient, the registered fractional setup shifts were grouped into systematic and random shifts. The average systematic dosimetric variations showed small dose deviation for the different cancer types (1.0%-3.0%) compared to the planned dose. Of the fifty patients, only three had percent differences larger than 5%. The average random dosimetric variations showed relatively small dose deviations (0.2%-1.1%) compared to the planned dose. None of the patients had percent differences larger than 5%. By examining the individual fractions of each patient, it is observed that only in 31 out of 1358 fractions the percent differences exceeded the border of 5%. These results indicate that the overall dosimetric impact from systematic and random variations is small and that the software is a capable platform for independent point dose validation for the Helical Tomotherapy modality. (C) 2012 Associazione Italiana di Fisica Medica.

  • 33. Ebner, Natalie C.
    et al.
    Johnson, Matthew R.
    Rieckmann, Anna
    Stockholm University, Faculty of Social Sciences, Aging Research Center (ARC), (together with KI).
    Durbin, Kelly A.
    Johnson, Marcia K.
    Fischer, Håkan
    Stockholm University, Faculty of Social Sciences, Department of Psychology. Stockholm University, Faculty of Social Sciences, Aging Research Center (ARC), (together with KI).
    Processing own-age vs. other-age faces: Neuro-behavioral correlates and effects of emotion2013In: NeuroImage, ISSN 1053-8119, E-ISSN 1095-9572, Vol. 78, 363-371 p.Article in journal (Refereed)
    Abstract [en]

    Age constitutes a salient feature of a face and signals group membership. There is evidence of greater attention to and better memory for own-age than other-age faces. However, little is known about the neural and behavioral mechanisms underlying processing differences for own-age vs. other-age faces. Even less is known about the impact of emotion expressed in faces on such own-age effects. Using fMRI, the present study examined brain activity while young and older adult participants identified expressions of neutral, happy, and angry young and older faces. Across facial expressions, medial prefrontal cortex, insula, and (for older participants) amygdala showed greater activity to own-age than other-age faces. These own-age effects in ventral medial prefrontal cortex and insula held for neutral and happy faces, but not for angry faces. This novel and intriguing finding suggests that processing of negative facial emotions under some conditions overrides age-of-face effects.

  • 34. Ebrahimian, T.
    et al.
    Le Gallic, C.
    Stefani, J.
    Dublineau, I.
    Yentrapalli, R.
    Harms-Ringdahl, Mats
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Haghdoost, Siamak
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Chronic Gamma-Irradiation Induces a Dose-Rate-Dependent Pro-inflammatory Response and Associated Loss of Function in Human Umbilical Vein Endothelial Cells2015In: Radiation Research, ISSN 0033-7587, Vol. 183, no 4, 447-454 p.Article in journal (Refereed)
    Abstract [en]

    A central question in radiation protection research is dose and dose-rate relationship for radiation-induced cardiovascular diseases. The response of endothelial cells to different low dose rates may contribute to help estimate risks for cardiovascular diseases by providing mechanistic understanding. In this study we investigated whether chronic low-dose-rate radiation exposure had an effect on the inflammatory response of endothelial cells and their function. Human umbilical vein endothelial cells (HUVECs) were chronically exposed to radiation at a dose of 1.4 mGy/h or 4.1 mGy/h for 1, 3, 6 or 10 weeks. We determined the pro-inflammatory profile of HUVECs before and during radiation exposure, and investigated the functional consequences of this radiation exposure by measuring their capacity to form vascular networks in matrigel. Expression levels of adhesion molecules such as E-selectin, ICAM-1 and VCAM-1, and the release of pro-inflammatory cytokines such as MCP-1, IL-6 and TNF-alpha were analyzed. When a total dose of 2 Gy was given at a rate of 4.1 mGy/h, we observed an increase in IL-6 and MCP-1 release into the cell culture media, but this was not observed at 1.4 mGy/h. The increase in the inflammatory profile induced at the dose rate of 4.1 mGy/h was also correlated with a decrease in the capacity of the HUVECs to form a vascular network in matrigel. Our results suggest that dose rate is an important parameter in the alteration of HUVEC inflammatory profile and function.

  • 35.
    Edén, Mattias
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Zeeman Truncation in NMR. I. The Role of Operator Commutation2015In: Concepts in magnetic resonance. Bridging education and research, ISSN 1546-6086, E-ISSN 1552-5023, Vol. 43, no 4, 91-108 p.Article in journal (Refereed)
    Abstract [en]

    Hamiltonians are of pivotal importance for describing and analyzing NMR experiments. However, the exact spin Hamiltonian operators are in practice not utilized, but merely a simplified form referred to either as the secular, Zeeman-truncated, or high-field Hamiltonian. It results after accounting for the dominating role of the Zeeman interaction relative to all other, much smaller NMR interactions, such as chemical shifts, through-bond, or through-space spin-spin couplings. In this article and the following one, we introduce the Zeeman truncation process to newcomers to NMR by thoroughly reviewing the options available for reducing the full Hamiltonian of a spin interaction to its Zeeman-truncated counterpart. The present paper considers time-independent Hamiltonians, where we discuss the criteria for performing truncation, highlighting the role of operator commutation by a simple formalism that is equivalent to application of lowest-order static perturbation theory. The validity of the approximations are illustrated by examining the explicit matrix representations of the exact and Zeeman truncated Hamiltonians, considering the NMR interactions relevant for systems of interacting spin-1/2 nuclei.

  • 36.
    Edén, Mattias
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Zeeman Truncation in NMR. II. Time Averaging in the Rotating Frame2015In: Concepts in magnetic resonance. Bridging education and research, ISSN 1546-6086, E-ISSN 1552-5023, Vol. 43, no 4, 109-126 p.Article in journal (Refereed)
    Abstract [en]

    The truncation of NMR interactions by the Zeeman Hamiltonian is here examined from a different perspective than that of our previous article [Concepts Magn. Reson., vol. 43A, pages 91-108 (2015)]: a Zeeman-truncated Hamiltonian is arranged by transforming the initially stationary operator of the NMR interaction into the rotating frame, followed by a time-averaging procedure over one Larmor period ( 2/0). We review the concept of an interaction frame, with focus on the rotating frame relevant for the Zeeman interaction, as well as the time-averaging procedure and the criteria for application of the resulting stationary Hamiltonian. A decisive advantage of this approach is its suitability for truncating time-dependent Hamiltonians, such as that of a radio-frequency (RF) field. Various options for reducing the time-dependent RF Hamiltonian into its stationary form are contrasted and thoroughly discussed. The role of Zeeman truncation is illustrated by examining the rotating-frame RF Hamiltonian associated with both on-resonance and off-resonance irradiation, where the time-independent operator character allows for applying the approximation strategies reviewed in our previous article.

  • 37.
    Edén Strindberg, Jerker
    Stockholm University, Faculty of Science, Medical Radiation Physics (together with KI).
    Evaluation of materials for ESR-dosimetry: Salts of formic and lactic acid as an example.2008Independent thesis Basic level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The technique of ESR-dosimetry and strategies for investigation of new materials as in regard to their applicability as ESR-dosimeters for radiotherapy has been reviewed. As an example six salts of formic and lactic acid has been evaluated. The applicability of the dosimeter has been judged by evaluating the tissue equivalence, radical yield, radical stability, spectral suitability, optimal readout parameters, dose response and sensitivity of the dosimetric system. Dependence of material characteristics and influence parameters has been analysed.

    The reviewed methods have been successfully used for evaluation of the new materials. Lithium formate has been shown to be a good candidate relative to the state of the art dosimeter of alanine. Using optimal readout parameters lithium formate has been shown to be nine times as sensitive but even at moderate settings lithium formate is more sensitive. The results for lithium formate are in accordance to those of previous studies. The signal intensity of sodium formate has also proved to be high but unfortunately the signal fades rapidly.

    Two new methods have been proposed as synthesis of the reviewed methods. The first allows flexible, effective and objective baseline correction of the ESR-spectrum. The second deals with dose response measurement by linear regression of the entire spectrum and was found to be successful in separating the spectral peaks of the induced radicals from the background signal.

  • 38.
    Eriksson, Lars
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Karolinska Institutet, Sweden; Siemens Healthcare Molecular Imaging, USA; University of Tennessee, USA.
    Conti, Maurizio
    Randoms and TOF gain revisited2015In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 60, no 4, 1613-1623 p.Article in journal (Refereed)
    Abstract [en]

    Time-of-flight (TOF) positron emission tomography (PET) typically reduces the variance in the images by a factor that is proportional to the size of the object to be scanned, and inversely proportional to the time resolution of the PET scanner. Attempts to better characterize this relationship and understand its limits have been published, showing that such gain also increases with random fraction. In this paper, new experimental and simulated data are analyzed and old results are incorporated in the study. The proportionality of TOF gain with time resolution is confirmed, the proportionality constant is measured, the effect of the randoms is validated, and the limit of the model for small objects is investigated.

  • 39.
    Ezzo, Issa
    Stockholm University, Faculty of Science, Medical Radiation Physics (together with KI).
    Determination of the conversion factor for the estimation of effective dose in lungs, urography and cardiac procedures2008Independent thesis Basic level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Patient dose in diagnostic radiology is usually expressed in terms of organ dose and effective dose. The latter is used as a measure of the stochastic risk. Determinations of these doses are obtained by measurements (Thermoluminescent dosemeters) or by calculations (Monte Carlo simulation).

    Conversion factors for the calculation of effective dose from dose-area product (DAP) values are commonly used to determine radiation dose in conventional x-ray imaging to realize radiation risks for different investigations, and for different ages. The exposure can easily be estimated by converting the DAP into an effective dose.

    The aim of this study is to determine the conversion factor in procedures by computing the ratio between effective dose and DAP for fluoroscopic cardiac procedures in adults and for conventional lung and urography examinations in children.

    Thermoluminescent dosemeters (TLD) were placed in an anthropomorphic phantom (Alderson Rando phantom) and child phantom (one year old) in order to measure the organ dose and compute the effective dose. A DAP meter was used to measure dose-area product.

    MC calculations of radiation transport in mathematical anthropomorphic phantoms were used to obtain the effective dose for the same conditions with DAP as input data.

    The deviation between the measured and calculated data was less than 10 %. The conversion factor for cardiac procedures varies between 0.19 mSvGy-1 cm-2 and 0.18 mSvGy-1 cm-2, for TLD respective MC. For paediatric simulation of a one year old phantom the average conversion factor for urography was 1.34 mSvGy-1 cm-2 and 1,48 mSvGy-1cm-2 for TLD respective MC. This conversion factor will decrease to 1.07 mSvGy-1 cm-2 using the TLD method, if the new ICRP (ICRP Publication 103) weighting factors were used to calculate the effective dose.

    For lung investigations, the conversion factor for children was 1.75 mSvGy-1 cm-2 using TLD, while this value was 1.62 mSvGy-1 cm-2 using MC simulation. The conversion value increased to 2.02 mSvGy-1 cm-2 using ICRP’s new recommendation for tissue weighting factors and child phantom.

  • 40. Francesc Barquinero, Joan
    et al.
    Beinke, Christina
    Borras, Mireia
    Buraczewska, Iwona
    Darroudi, Firouz
    Gregoire, Eric
    Hristova, Rositsa
    Kulka, Ulrike
    Lindholm, Carita
    Moreno, Mercedes
    Moquet, Jayne
    Oestreicher, Ursula
    Jesus Prieto, M.
    Pujol, Monica
    Ricoul, Michelle
    Sabatier, Laure
    Sommer, Sylwester
    Sun, Mingzhu
    Wojcik, Andrzej
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Barrios, Leonardo
    RENEB biodosimetry intercomparison analyzing translocations by FISH2017In: International Journal of Radiation Biology, ISSN 0955-3002, E-ISSN 1362-3095, Vol. 93, no 1, 30-35 p.Article in journal (Refereed)
    Abstract [en]

    Purpose: In the framework of RENEB, several biodosimetry exercises were conducted analyzing different endpoints. Among them, the analysis of translocations is considered the most useful method for retrospective biodosimetry due to the relative stability of their frequency with post irradiation time. The aim of this study was to harmonize the accuracy of translocation-based biodosimetry within the RENEB consortium. Materials and methods: An initial telescoring exercise analyzing FISH metaphase images was done to harmonize chromosome aberration descriptions. Then two blind intercomparison exercises (IE) were performed, by sending irradiated blood samples to each partner. Samples were cultured and stained by each partner using their standard protocol and translocation frequency was used to produce dose estimates. Results: The coefficient of variation in the 1st IE (CV = 0.34) was higher than in the 2nd IE (CV = 0.16 and 0.23 in the two samples analyzed), for the genomic frequency of total translocations. Z-score analysis revealed that eight out of 10 and 17 out of 20 dose estimates were satisfactory in the 1st and 2nd IE, respectively. Conclusions: The results obtained indicate that, despite the problems identified in few partners, which can be corrected, the RENEB consortium is able to carry out retrospective biodosimetry analyzing the frequency of translocations by FISH.

  • 41. Francis, Z.
    et al.
    Incerti, S.
    Capra, R.
    Mascialino, Barbara
    Stockholm University, Faculty of Science, Department of Physics.
    Montarou, G.
    Stepan, V.
    Villagrasa, C.
    Molecular scale track structure simulations in liquid water using the Geant4-DNA Monte-Carlo processes2011In: Applied Radiation and Isotopes, ISSN 0969-8043, E-ISSN 1872-9800, Vol. 69, no 1, 220-226 p.Article in journal (Refereed)
    Abstract [en]

    This paper presents a study of energy deposits induced by ionising particles in liquid water at the molecular scale Particles track structures were generated using the Geant4-DNA processes of the Geant4 Monte-Carlo toolkit These processes cover electrons (0 025 eV-1 MeV) protons (1 keV-100 MeV) hydrogen atoms (1 keV-100 MeV) and alpha particles (10 keV-40 MeV) including their different charge states Electron ranges and lineal energies for protons were calculated in nanometric and micrometric volumes

  • 42.
    Garzón, Benjamin
    et al.
    Stockholm University, Faculty of Social Sciences, Aging Research Center (ARC), (together with KI).
    Sitnikov, Rouslan
    Bäckman, Lars
    Stockholm University, Faculty of Social Sciences, Aging Research Center (ARC), (together with KI).
    Kalpouzos, Grégoria
    Stockholm University, Faculty of Social Sciences, Aging Research Center (ARC), (together with KI).
    Can transverse relaxation rates in deep gray matter be approximated from functional and T-2-weighted FLAIR scans for relative brain iron quantification?2017In: Magnetic Resonance Imaging, ISSN 0730-725X, E-ISSN 1873-5894, Vol. 40, 75-82 p.Article in journal (Refereed)
    Abstract [en]

    Alterations in iron concentration in certain deep gray matter regions are known to occur in aging and several clinical conditions. In vivo measurements of R-2* transverse relaxation rates and quantitative susceptibility mapping (QSM) have been shown to be strongly correlated with iron concentration in tissue, but their calculation requires the acquisition of a multi-echo gradient recalled echo sequence (MGRE). In the current study, we examined the feasibility of approximating R-2* rates using metrics derived from fMRI-EPI and T-2-weighted FLAIR images, which are widely available. In a sample of 40 healthy subjects, we obtained these metrics (v(EPI) and v(FLAIR)), as well as R-2* rates and QSM estimates, and found significant correlations between v(EPI) and v(FLAIR) and R-2* rates in several subcortical gray matter regions known to accumulate iron, but not in a control corticospinal white matter region. These relationships were preserved after referencing v(EPI) and v(FLAIR) with respect to the values in the control region. Effect sizes (above 0.5 for some of the regions, particularly the largest ones) were calculated and put in relation to those of the correlation between QSM and R-2* rates. We propose that the metrics described here may be applied, possibly in a retrospective fashion, to analyze datasets with available EPI or T-2-weighted FLAIR scans (and lacking a MGRE sequence), to devise new hypotheses regarding links between iron concentration in brain tissue and other variables of interest.

  • 43.
    Geghamyan, Narine
    Stockholm University, Faculty of Science, Medical Radiation Physics (together with KI).
    Estimation of foetal radiation dose to occupationally exposed staff in diagnostic radiology and nuclear medicine.2006Independent thesis Basic level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The protection of the unborn child in pregnant women from ionizing radiation is very important because the foetus is particularly sensitive to the effects of radiation. In case of pregnant members of staff working with ionising radiation, the unborn child is treated as a member of the general public, and a dose limit of 1 mSv during pregnancy is applied in order to protect the foetus.

    The purpose of this work was to collect relevant information on exposure conditions and entrance doses of occupationally exposed workers in diagnostic radiology and nuclear medicine, and to give guidelines on how to estimate foetal doses for pregnant staff in such workplaces.

    With X-ray procedures, an accumulated dose of 2 mSv during pregnancy, measured on the trunk (breast or waist) and behind a lead apron, is sufficient to ensure a foetal dose below 1 mSv. For staff working with nuclear medicine, the corresponding limit is 1.5 mSv taking into account external exposure from 99mTc. When internal contamination cannot be neglected, additional precautions need to be considered.

  • 44. Goma, C.
    et al.
    Andreo, Pedro
    Stockholm University, Faculty of Science, Department of Physics. Karolinska Institutet.
    Sempau, J.
    Spencer-Attix water/medium stopping-power ratios for the dosimetry of proton pencil beams2013In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 58, no 8, 2509-2522 p.Article in journal (Refereed)
    Abstract [en]

    This paper uses Monte Carlo simulations to calculate the Spencer-Attix water/medium stopping-power ratios (s(w, med)) for the dosimetry of scanned proton pencil beams. It includes proton energies from 30 to 350 MeV and typical detection materials such as air (ionization chambers), radiochromic film, gadolinium oxysulfide (scintillating screens), silicon and lithium fluoride. Track-ends and particles heavier than protons were found to have a negligible effect on the water/air stopping-power ratios (s(w, air)), whereas the mean excitation energy values were found to carry the largest source of uncertainty. The initial energy spread of the beam was found to have a minor influence on the s(w, air) values in depth. The water/medium stopping-power ratios as a function of depth in water were found to be quite constant for air and radiochromic film-within 2.5%. Also, the s(w, med) values were found to have no clinically relevant dependence on the radial distance-except for the case of gadolinium oxysulfide and proton radiography beams. In conclusion, the most suitable detection materials for depth-dose measurements in water were found to be air and radiochromic film active layer, although a small correction is still needed to compensate for the different s(w, med) values between the plateau and the Bragg peak region. Also, all the detection materials studied in this work-except for gadolinium oxysulfide-were found to be suitable for lateral dose profiles and field-specific dose distribution measurements in water.

  • 45.
    Gorka, Bartosz
    et al.
    Stockholm University, Faculty of Science, Medical Radiation Physics (together with KI).
    Fernandez-Varea, Jose Maria
    Nilsson, Bo
    Stockholm University, Faculty of Science, Medical Radiation Physics (together with KI).
    Panettieri, Vanessa
    Optimization of a tissue-equivalent CVD-diamond detector prototype by Monte Carlo calculations2007Other (Other academic)
  • 46.
    Grafström, Jonas
    Stockholm University, Faculty of Science, Medical Radiation Physics (together with KI).
    Determination of the effective volume of a detector2007Independent thesis Basic level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    A method to establish the boundaries of the sensitive volume for a chosen detector to within 50µm (as specified by Elekta Instuments AB) was investigated and is presented in this project. The detector studied was fixed to a positioning system with possibility to move with sub micrometer increments, and scanned in a narrow photon field. The detectors used for the experiment were silicon diodes and a pair of diamond detectors. The silicon diodes showed great promise for future study; two radiotherapy silicon diodes and one electrical component silicon diode were used. The electrical component silicon diode produced a surprisingly sharp dose profile compared with the medical silicon diodes. The diamond detectors gave no stable results at all.

    As a radiation source 60Co proved most feasible, but a diagnostic x-ray source was also tested as well as a 99mTc source. These radiation sources were also examined with a modified Penelope code, i.e. Monte Carlo simulations. What became very obvious with the Monte Carlo simulations was the importance of the line up, which was never satisfactory.

    To limit the sensitive volume of these detectors to within the desired boundaries showed great difficulty and was not achieved in this project.

  • 47. Grandy, Thomas H.
    et al.
    Werkle-Bergner, Markus
    Chicherio, Christian
    Lövden, Martin
    Stockholm University, Faculty of Social Sciences, Aging Research Center (ARC), (together with KI).
    Schmiedek, Florian
    Lindenberger, Ulman
    Individual alpha peak frequency is related to latent factors of general cognitive abilities2013In: NeuroImage, ISSN 1053-8119, E-ISSN 1095-9572, Vol. 79, 10-18 p.Article in journal (Refereed)
    Abstract [en]

    Some eighty years after the discovery of the human electroencephalogram (EEG) and its dominant rhythm, alpha (similar to 10 Hz), the neurophysiological functions and behavioral correlates of alpha oscillations are still under debate. Similarly, the biological mechanisms contributing to the general factor of intelligence, or g, have been under scrutiny for decades. Individual alpha frequency (IAF), a trait-like parameter of the EEG, has been found to correlate with individual differences in cognitive performance and cognitive abilities. Informed by large-scale theories of neural organization emphasizing the general functional significance of oscillatory activity, the present study replicates and extends these findings by testing the hypothesis that IAF is related to intelligence at the level of g, rather than at the level of specific cognitive abilities. Structural equation modeling allowed us to statistically control for measurement error when estimating the association between IAF and intellectual functioning. In line with our hypothesis, we found a statistically reliable and substantial correlation between IAF and g (r = .40). The magnitude of this correlation did not differ significantly between younger and older adults, and captured all of the covariation between IAF and the cognitive abilities of reasoning, memory, and perceptual speed. The observed association between IAF and g provides a parsimonious explanation for the commonly observed diffuse pattern of correlations between IAF and cognitive performance. We conclude that IAF is a marker of global architectural and functional properties of the human brain.

  • 48. Hauptmann, Monika
    et al.
    Haghdoost, Siamak
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Gomolka, Maria
    Sarioglu, Hakan
    Ueffing, Marius
    Dietz, Anne
    Kulka, Ulrike
    Unger, Kristian
    Babini, Gabriele
    Harms-Ringdahl, Mats
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Ottolenghi, Andrea
    Hornhardt, Sabine
    Differential Response and Priming Dose Effect on the Proteome of Human Fibroblast and Stem Cells Induced by Exposure to Low Doses of Ionizing Radiation2016In: Radiation Research, ISSN 0033-7587, E-ISSN 1938-5404, Vol. 185, no 3, 299-312 p.Article in journal (Refereed)
    Abstract [en]

    It has been suggested that a mechanistic understanding of the cellular responses to low dose and dose rate may be valuable in reducing some of the uncertainties involved in current risk estimates for cancer- and non-cancer-related radiation effects that are inherited in the linear nothreshold hypothesis. In this study, the effects of low-dose radiation on the proteome in both human fibroblasts and stem cells were investigated. Particular emphasis was placed on examining: 1. the dose-response relationships for the differential expression of proteins in the low-dose range (40-140 mGy) of low-linear energy transfer (LET) radiation; and 2. the effect on differential expression of proteins of a priming dose given prior to a challenge dose (adaptive response effects). These studies were performed on cultured human fibroblasts (VH10) and human adipose-derived stem cells (ADSC). The results from the VH10 cell experiments demonstrated that low-doses of low-LET radiation induced unique patterns of differentially expressed proteins for each dose investigated. In addition, a low priming radiation dose significantly changed the protein expression induced by the subsequent challenge exposure. In the ADSC the number of differentially expressed proteins was markedly less compared to VH10 cells, indicating that ADSC differ in their intrinsic response to low doses of radiation. The proteomic results are further discussed in terms of possible pathways influenced by low-dose irradiation.

  • 49.
    Hollmark, Malin
    Stockholm University, Faculty of Science, Medical Radiation Physics (together with KI).
    Absorbed dose and biological effect in light ion therapy2008Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Radiation therapy with light ions improves treatment outcome for a number of tumor types. The advantageous dose distributions of light ion beams en-able exceptional target conformity, which assures high dose delivery to the tumor while minimizing the dose to surrounding normal tissues. The demand of high target conformity necessitates development of accurate methods to calculate absorbed dose distributions. This is especially important for heavy charged particle irradiation, where the patient is exposed to a complex radia-tion field of primary and secondary ions.

    The presented approach combines accurate Monte Carlo calculations using the SHIELD-HIT07 code with a fast analytical pencil beam model, to pro-vide dose distributions of light ions. The developed model allows for ana-lytical descriptions of multiple scattering and energy loss straggling proc-esses of both primary ions and fragments, transported in tissue equivalent media. By applied parameterization of the radial spread of fragments, im-proved description of radial dose distributions at every depth is obtained. The model provides a fast and accurate tool of practical value in clinical work.

    Compared to conventional radiation modalities, an enhanced tissue response is seen after light ion irradiation and biological optimization calls for accu-rate model description and prediction of the biological effects of ion expo-sure. In a joint study, the performance of some radiobiological models is compared for facilitating the development towards more robust and precise models. Specifically, cell survival after exposure to various ion species is modeled by a fast analytical cellular track structure approach in conjunction with a simple track-segment model of ion beam transport. Although the stud-ies show that descriptions of complex biological effects of ion beams, as given by simple radiobiological models, are approximate, the models may yet be useful in analyzing clinical results and designing new strategies for ion therapy.

  • 50.
    Hultqvist, Martha
    Stockholm University, Faculty of Science, Medical Radiation Physics (together with KI).
    Analysis of the uncertainties in the IAEA/WHO TLD postal dose audit programme2006Independent thesis Basic level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The International Atomic Energy Agency (IAEA) and the World Health Organisation (WHO) operate the IAEA/WHO TLD postal dose audit programme. The purpose of the programme is to verify the beam calibration in radiotherapy centres in developing countries and to check the Secondary Standards Dosimetry Laboratories (SSDLs). Thermoluminescence dosimeters (TLDs) are used as transfer dosimeters and the evaluation of these are done at the IAEA Dosimetry Laboratory. In the present work the uncertainties in the process of dose determination from TLD readings have been evaluated.

    The analysis comprises the TLD reading reproducibility, uncertainties in the calibration coefficient, and uncertainties in factors correcting for fading of TL signal, influence of TLD holder, energy response and dose response non-linearity. The individual uncertainties were combined to estimate the total uncertainty in the evaluated dose from TLD readings. Experimental data from 2001-2005 were used in the analysis.

    The total uncertainty has been estimated to be 1.2 % for irradiations with 60Co -rays and 1.6 % for irradiations with high-energy X-rays. Results from irradiations by the Bureau International des Poids et Mesures (BIPM), Primary Standard Dosimetry Laboratories (PSDLs), Secondary Standard Dosimetry Laboratories (SSDLs) and reference centres compare favourably with the estimated uncertainties.

    The largest uncertainty components are in the energy correction factor (for high-energy X-rays) with a value of 1.1 % and in the dose response non-linearity correction factor with a value of 0.9 %.

    It has been shown that the acceptance limits of 5 % for TLD results of hospitals and 3.5 % for SSDLs are justified when related to the uncertainties in the dose calculations and the uncertainty in the determination of absorbed dose to water at the centre, as discussed in IAEA TRS-398 (IAEA, 2000), provided that it is followed.

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