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  • 51. Fernández-Varea, José M.
    et al.
    Gonzalez-Muñoz, Gloria
    Galassi, Mariel E.
    Wiklund, Kristin
    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).
    Ahnesjö, Anders
    Tilly, Nina
    Limitations (and merits) of PENELOPE as a track-structure code2012In: International Journal of Radiation Biology, ISSN 0955-3002, E-ISSN 1362-3095, Vol. 88, no 1-2, p. 66-70Article in journal (Refereed)
    Abstract [en]

    Purpose: To outline the limitations of PENELOPE (acronym of PENetration and Energy LOss of Positrons and Electrons) as a track-structure code, and to comment on modifications that enable its fruitful use in certain microdosimetry and nanodosimetry applications.

    Methods: Attention is paid to the way in which inelastic collisions of electrons are modelled and to the ensuing implications for microdosimetry analysis.

    Results: Inelastic mean free paths and collision stopping powers calculated with PENELOPE and two well-known optical-data models are compared. An ad hoc modification of PENELOPE is summarized where ionization and excitation of liquid water by electron impact is simulated using tables of realistic differential and total cross sections.

    Conclusions: PENELOPE can be employed advantageously in some track-structure applications provided that the default model for inelastic interactions of electrons is replaced by suitable tables of differential and total cross sections.

  • 52. 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, p. 30-35Article 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.

  • 53. 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, p. 220-226Article 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

  • 54.
    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, p. 75-82Article 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.

  • 55. Gałecki, Maciej
    et al.
    Tartas, Adrianna
    Szymanek, Agata
    Sims, Emma
    Lundholm, Lovisa
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Sollazzo, Alice
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Cheng, Lei
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Fujishima, Yohei
    Yoshida, Mitsuaki A.
    Żygierewicz, Jarosław
    Wojcik, Andrzej
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute. Jan Kochanowski University, Poland.
    Brzozowska-Wardecka, Beata
    Precision of scoring radiation-induced chromosomal aberrations and micronuclei by unexperienced scorers2019In: International Journal of Radiation Biology, ISSN 0955-3002, E-ISSN 1362-3095, Vol. 95, no 9, p. 1251-1258Article in journal (Refereed)
    Abstract [en]

    Purpose: Dose assessment plays an important role in case of radiological accidents and can be performed by scoring structural changes of chromosome morphology induced in cells by ionizing radiation. The results of such a test are biased by scorer experience, therefore, simple to learn assays are recommended to be used when fast analysis of a large amount of data is needed. The aim of this study was to compare the performance of two radiobiological assays - chromosomal aberrations and micronuclei - by unexperienced scorers with the reference values generated by an expert.

    Materials and methods: Each participant of an EU-funded two-week radiobiology course was asked to score Chinese hamster ovary cells exposed to gamma radiation up to 4 Gy. The congruence of students' and expert's scores at each dose and the coherence of the dose-response curve parameters between the students were investigated.

    Results: Micronucleus test tended to be faster and easier to learn than scoring chromosomal aberrations. However, both assays carried out by inexperienced students showed reasonable dose-response curves.

    Conclusions: In the case of a large radiological accident involving many casualties, the unexperienced scorers would support the process of biodosimetric triage by cytogenetic biological dosimetry.

  • 56.
    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.

  • 57. 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, p. 2509-2522Article 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.

  • 58.
    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)
  • 59.
    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.

  • 60. 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, p. 10-18Article 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.

  • 61. Grzanka, Leszek
    et al.
    Ardenfors, Oscar
    Stockholm University, Faculty of Science, Department of Physics.
    Bassler, Niels
    Stockholm University, Faculty of Science, Department of Physics. Aarhus University, Denmark.
    MONTE CARLO SIMULATIONS OF SPATIAL LET DISTRIBUTIONS IN CLINICAL PROTON BEAMS2018In: Radiation Protection Dosimetry, ISSN 0144-8420, E-ISSN 1742-3406, Vol. 180, no 1-4, p. 296-299Article in journal (Refereed)
    Abstract [en]

    The linear energy transfer (LET) is commonly used as a parameter which describes the quality of the radiation applied in radiation therapy with fast ions. In particular in proton therapy, most models which predict the radiobiological properties of the applied beam, are fitted to the dose-averaged LET, LETd. The related parameter called the fluence-or track-averaged LET, LETt, is less frequently used. Both LETt and in particular LETd depends profoundly on the encountered secondary particle spectrum. For proton beams including all secondary particles, LETd may reach more than 3 keV/um in the entry channel of the proton field. However, typically the charged particle spectrum is only averaged over the primary and secondary protons, which is in the order of 0.5 keV/um for the same region. This is equal to assuming that the secondary particle spectrum from heavier ions is irrelevant for the resulting radiobiology, which is an assertion in the need of closer investigation. Models which rely on LETd should also be clear on what type of LETd is used, which is not always the case. Within this work, we have extended the Monte Carlo particle transport code SHIELD-HIT12A to provide dose-and track-average LET-maps for ion radiation therapy treatment plans.

  • 62.
    Gustafsson, Anders
    Stockholm University, Faculty of Science.
    Development of a versatile algorithm for optimization of radiation therapy1996Doctoral thesis, comprehensive summary (Other academic)
  • 63. 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, p. 299-312Article 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.

  • 64.
    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.

  • 65. Homann, Manijeh Vafa
    et al.
    Emami, S. Noushin
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Yman, Victor
    Stenström, Christine
    Sondén, Klara
    Ramström, Hanna
    Karlsson, Mattias
    Asghar, Muhammad
    Färnert, Anna
    Detection of Malaria Parasites After Treatment in Travelers: A 12-months Longitudinal Study and Statistical Modelling Analysis2017In: EBioMedicine, ISSN 0360-0637, E-ISSN 2352-3964, Vol. 25, p. 66-72Article in journal (Refereed)
    Abstract [en]

    The rapid clearance of malaria parasite DNA from circulation has widely been accepted as a fact without being systemically investigated. We assessed the persistence of parasite DNA in travelers treated for Plasmodium falciparum malaria in a malaria-free area. Venous blood was collected at the time of admission and prospectively up to one year. DNA and RNA were extracted and analyzed using species-specific and gametocyte-specific real-time PCR as well as merozoite surface protein 2 (msp2)-PCR. In 31 successfully treated individuals, asexual parasites were seen by microscopy until two days after treatment, whereas parasite DNA was detected by msp2- and species-specific PCR up to days 31 and 42, respectively. Statistical modelling predicted 26% (+/- 0.05 SE) species-specific PCR positivity until day 40 and estimated 48 days for all samples to become PCR negative. Gametocytes were detected by microscopy and PCR latest two days after treatment. C-T values correlated well with microscopy-defined parasite densities before but not after treatment started. These results reveal that PCR positivity can persist several weeks after treatment without evidence of viable sexual or asexual parasites, indicating that PCR may overestimate parasite prevalence after treatment.

  • 66.
    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.

  • 67.
    Hultqvist, Martha
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Lazzeroni, Marta
    Botvina, Alexander
    Gudowska, Irena
    Stockholm University, Faculty of Science, Department of Physics.
    Sobolevsky, Nikolai
    Brahme, Anders
    Evaluation of nuclear reaction cross-sections and fragment yields in carbon beams using the SHIELD-HIT Monte Carlo code. Comparison with experiments2012In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 57, no 13, p. 4369-4385Article in journal (Refereed)
    Abstract [en]

    In light ion therapy, the knowledge of the spectra of both primary and secondary particles in the target volume is needed in order to accurately describe the treatment. The transport of ions in matter is complex and comprises both atomic and nuclear processes involving primary and secondary ions produced in the cascade of events. One of the critical issues in the simulation of ion transport is the modeling of inelastic nuclear reaction processes, in which projectile nuclei interact with target nuclei and give rise to nuclear fragments. In the Monte Carlo code SHIELD-HIT, inelastic nuclear reactions are described by the Many Stage Dynamical Model (MSDM), which includes models for the different stages of the interaction process. In this work, the capability of SHIELD-HIT to simulate the nuclear fragmentation of carbon ions in tissue-like materials was studied. The value of the parameter., which determines the so-called freeze-out volume in the Fermi break-up stage of the nuclear interaction process, was adjusted in order to achieve better agreement with experimental data. In this paper, results are shown both with the default value k = 1 and the modified value k = 10 which resulted in the best overall agreement. Comparisons with published experimental data were made in terms of total and partial charge-changing cross-sections generated by the MSDM, as well as integral and differential fragment yields simulated by SHIELD-HIT in intermediate and thick water targets irradiated with a beam of 400 MeV u(-1) C-12 ions. Better agreement with the experimental data was in general obtained with the modified parameter value (k = 10), both on the level of partial charge-changing cross-sections and fragment yields.

  • 68. Høye, Ellen Marie
    et al.
    Skyt, Peter S.
    Balling, Peter
    Muren, Ludvig P.
    Taasti, Vicki T.
    Swakoń, Jan
    Mierzwińska, Gabriela
    Rydygier, Marzena
    Bassler, Niels
    Stockholm University, Faculty of Science, Department of Physics. Aarhus University, Denmark.
    Petersen, Jørgen B. B.
    Chemically tuned linear energy transfer dependent quenching in a deformable, radiochromic 3D dosimeter2017In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 62, no 4, p. N73-N89Article in journal (Refereed)
    Abstract [en]

    Most solid-state detectors, including 3D dosimeters, show lower signal in the Bragg peak than expected, a process termed quenching. The purpose of this study was to investigate how variation in chemical composition of a recently developed radiochromic, silicone-based 3D dosimeter influences the observed quenching in proton beams. The dependency of dose response on linear energy transfer, as calculated through Monte Carlo simulations of the dosimeter, was investigated in 60 MeV proton beams. We found that the amount of quenching varied with the chemical composition: peak-to-plateau ratios (1 cm into the plateau) ranged from 2.2 to 3.4, compared to 4.3 using an ionization chamber. The dose response, and thereby the quenching, was predominantly influenced by the curing agent concentration, which determined the dosimeter's deformation properties. The dose response was found to be linear at all depths. All chemical compositions of the dosimeter showed dose-rate dependency; however this was not dependent on the linear energy transfer. Track-structure theory was used to explain the observed quenching effects. In conclusion, this study shows that the silicone-based dosimeter has potential for use in measuring 3D-dose-distributions from proton beams.

  • 69. Iannilli, Emilia
    et al.
    Wiens, Stefan
    Stockholm University, Faculty of Social Sciences, Department of Psychology.
    Arshamian, Artin
    Stockholm University, Faculty of Social Sciences, Department of Psychology.
    Seo, Han-Seok
    A spatiotemporal comparison between olfactory and trigeminal event-related potentials2013In: NeuroImage, ISSN 1053-8119, E-ISSN 1095-9572, Vol. 77, p. 254-261Article in journal (Refereed)
    Abstract [en]

    The present study compared the temporal and spatial aspects of human olfactory and trigeminal processing. A relatively selective trigeminal stimulus, CO2, and a relatively selective olfactory stimulus, H2S, were delivered with an olfactometer to young, healthy volunteers. The analysis was performed in a classical (5-electrode, main ERPs peaks) and modern approach (high topographical resolution, inverse solution, source localization). Results of microstate segmentation highlighted 5 maps that generally described the two processes at cerebral level. The trigeminal response differed from the olfactory response up to 300 ms after stimulus onset. In this time range, source analysis pointed out that the olfactory stimulation involved olfactory related areas, while trigeminal stimulation involved noxious/somatosensoiy specific brain areas. Moreover, from 300 ms on our data showed a similarity between the two processes. Statistical parametrical mapping of the differences between conditions suggested greater activation in a specific motor/sniffing network for the CO2 stimulation (probably related to a regulation of the potential noxious stimulus) and a greater activation of the ipsilateral primary olfactory cortex for H2S.

  • 70.
    Iqeilan, Nabil
    Stockholm University, Faculty of Science, Medical Radiation Physics (together with KI).
    Entrance Skin Dose Measurement Using GafChromic Dosimetry Film for Patients Undergoing Coronary Angiography (CA) and Percutaneous Transluminal Coronary Angiography (PTCA) Procedures2007Independent thesis Basic level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Interventional radiological procedures often require long fluoroscopic exposure times and high levels of radiation exposure to patients, which often are higher than most radiological examinations except for computed tomography (CT) whose effective doses can be higher, and in addition to having radiation risks that are higher for both patient and medical staff. Therefore it is important to monitor and map the radiation entrance exposure to the patients, to minimize the probability of skin injury, and to detect areas of overlapping radiation fields. The aim of this thesis is to evaluate patient doses in interventional radiology procedures using a new GAFCHROMIC-XR TYPE R DOSIMETER MEDIA X-ray Dosimetry film, which allows mapping of the skin dose distribution, when placed closer to the skin. These radiochromic films can be characterized by a power response dose function when plotting pixel value versus air kerma and have been calibrated up to 5 Gy when using a flatbed scanner. Image analysis was performed using the red channel component of standard the RGB (Red, Green, and Blue) color space image. The association between the Maximum Entrance Skin Doses (MESD) and Dose Area Product (DAP) values for two interventional procedures; coronary angiography (CA), and percutaneous transluminal coronary angiography (PTCA) is investigated.

  • 71.
    Janek, Sara
    et al.
    Stockholm University, Faculty of Science, Medical Radiation Physics (together with KI). Stockholm University, Faculty of Science, Department of Physics.
    Svensson, Roger
    Stockholm University, Faculty of Science, Medical Radiation Physics (together with KI).
    Jonsson, Cathrine
    Stockholm University, Faculty of Science, Medical Radiation Physics (together with KI).
    Brahme, Anders
    Stockholm University, Faculty of Science, Medical Radiation Physics (together with KI).
    Development of dose delivery verification by PET imaging of photonuclear reactions following high energy photon therapy2006In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 51, no 22, p. 5769-Article in journal (Refereed)
    Abstract [en]

    A method for dose delivery monitoring after high energy photon therapy has been investigated based on positron emission tomography (PET). The technique is based on the activation of body tissues by high energy bremsstrahlung beams, preferably with energies well above 20 MeV, resulting primarily in 11C and 15O but also 13N, all positron-emitting radionuclides produced by photoneutron reactions in the nuclei of 12C, 16O and 14N. A PMMA phantom and animal tissue, a frozen hind leg of a pig, were irradiated to 10 Gy and the induced positron activity distributions were measured off-line in a PET camera a couple of minutes after irradiation. The accelerator used was a Racetrack Microtron at the Karolinska University Hospital using 50 MV scanned photon beams. From photonuclear cross-section data integrated over the 50 MV photon fluence spectrum the predicted PET signal was calculated and compared with experimental measurements. Since measured PET images change with time post irradiation, as a result of the different decay times of the radionuclides, the signals from activated 12C, 16O and 14N within the irradiated volume could be separated from each other. Most information is obtained from the carbon and oxygen radionuclides which are the most abundant elements in soft tissue. The predicted and measured overall positron activities are almost equal (−3%) while the predicted activity originating from nitrogen is overestimated by almost a factor of two, possibly due to experimental noise. Based on the results obtained in this first feasibility study the great value of a combined radiotherapy–PET–CT unit is indicated in order to fully exploit the high activity signal from oxygen immediately after treatment and to avoid patient repositioning. With an RT–PET–CT unit a high signal could be collected even at a dose level of 2 Gy and the acquisition time for the PET could be reduced considerably. Real patient dose delivery verification by means of PET imaging seems to be applicable provided that biological transport processes such as capillary blood flow containing mobile 15O and 11C in the activated tissue volume can be accounted for.

  • 72.
    Janek Strååt, Sara
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Karolinska Institutet, Sweden.
    Andreassen, Björn
    Stockholm University, Faculty of Science, Department of Physics. Karolinska Institutet, Sweden.
    Jonsson, Cathrine
    Noz, Marilyn E.
    Maguire Jr, Gerald Q.
    Nafstadius, Peder
    Näslund, Ingemar
    Schoenahl, Frederic
    Brahme, Anders
    Stockholm University, Faculty of Science, Department of Physics. Karolinska Institutet, Sweden.
    Clinical application of in vivo treatment delivery verification based on PET/CT imaging of positron activity induced at high energy photon therapy2013In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 58, no 16, p. 5541-5553Article in journal (Refereed)
    Abstract [en]

    The purpose of this study was to investigate in vivo verification of radiation treatment with high energy photon beams using PET/CT to image the induced positron activity. The measurements of the positron activation induced in a preoperative rectal cancer patient and a prostate cancer patient following 50 MV photon treatments are presented. A total dose of 5 and 8 Gy, respectively, were delivered to the tumors. Imaging was performed with a 64-slice PET/CT scanner for 30 min, starting 7 min after the end of the treatment. The CT volume from the PET/CT and the treatment planning CT were coregistered by matching anatomical reference points in the patient. The treatment delivery was imaged in vivo based on the distribution of the induced positron emitters produced by photonuclear reactions in tissue mapped on to the associated dose distribution of the treatment plan. The results showed that spatial distribution of induced activity in both patients agreed well with the delivered beam portals of the treatment plans in the entrance subcutaneous fat regions but less so in blood and oxygen rich soft tissues. For the preoperative rectal cancer patient however, a 2 +/- (0.5) cm misalignment was observed in the cranial-caudal direction of the patient between the induced activity distribution and treatment plan, indicating a beam patient setup error. No misalignment of this kind was seen in the prostate cancer patient. However, due to a fast patient setup error in the PET/CT scanner a slight mis-position of the patient in the PET/CT was observed in all three planes, resulting in a deformed activity distribution compared to the treatment plan. The present study indicates that the induced positron emitters by high energy photon beams can be measured quite accurately using PET imaging of subcutaneous fat to allow portal verification of the delivered treatment beams. Measurement of the induced activity in the patient 7 min after receiving 5 Gy involved count rates which were about 20 times lower than that of a patient undergoing standard F-18-FDG treatment. When using a combination of short lived nuclides such as O-15 (half-life: 2 min) and C-11 (half-life: 20 min) with low activity it is not optimal to use clinical reconstruction protocols. Thus, it might be desirable to further optimize reconstruction parameters as well as to address hardware improvements in realizing in vivo treatment verification with PET/CT in the future. A significant improvement with regard to O-15 imaging could also be expected by having the PET/CT unit located close to the radiation treatment room.

  • 73.
    Janek Strååt, Sara
    et al.
    Stockholm University, Faculty of Science, Medical Radiation Physics (together with KI). Stockholm University, Faculty of Science, Department of Physics.
    Jacobsson, Hans
    Andreassen, Björn
    Näslund, Ingemar
    Jonsson, Cathrine
    Dynamic PET/CT measurements of induced positron activity in a prostate cancer patient after 50 MV photon radiation therapyIn: Journal of Nuclear Medicine, ISSN 0161-5505, E-ISSN 1535-5667Article in journal (Other academic)
  • 74. Jiménez-Ortega, E.
    et al.
    Ureba, Ana
    Stockholm University, Faculty of Science, Medical Radiation Physics (together with KI). Instituto de Biomedicina de Sevilla, Spain.
    Vargas, A.
    Baeza, J. A.
    Wals-Zurita, A.
    García-Gómez, J.
    Barbeiro, A. R.
    Leal, A.
    Dose painting by means of Monte Carlo treatment planning at the voxel level2017In: Physica medica (Testo stampato), ISSN 1120-1797, E-ISSN 1724-191X, Vol. 42, p. 339-344Article in journal (Refereed)
    Abstract [en]

    Purpose: To develop a new optimization algorithm to carry out true dose painting by numbers (DPBN) planning based on full Monte Carlo (MC) calculation.

    Methods: Four configurations with different clustering of the voxel values from PET data were proposed. An optimization method at the voxel level under Lineal Programming (LP) formulation was used for an inverse planning and implemented in CARMEN, an in-house Monte Carlo treatment planning system.

    Results: Beamlet solutions fulfilled the objectives and did not show significant differences between the different configurations. More differences were observed between the segment solutions. The plan for the dose prescription map without clustering was the better solution.

    Conclusions: LP optimization at voxel level without dose-volume restrictions can carry out true DPBN planning with the MC accuracy.

  • 75.
    Kalpouzos, Grégoria
    et al.
    Stockholm University, Faculty of Social Sciences, Aging Research Center (ARC), (together with KI).
    Eriksson, Johan
    Sjölie, Daniel
    Molin, Jonas
    Nyberg, Lars
    Neurocognitive systems related to real-world prospective memory.2010In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 5, no 10, p. e13304-Article in journal (Refereed)
    Abstract [en]

    BACKGROUND: Prospective memory (PM) denotes the ability to remember to perform actions in the future. It has been argued that standard laboratory paradigms fail to capture core aspects of PM.

    METHODOLOGY/PRINCIPAL FINDINGS: We combined functional MRI, virtual reality, eye-tracking and verbal reports to explore the dynamic allocation of neurocognitive processes during a naturalistic PM task where individuals performed errands in a realistic model of their residential town. Based on eye movement data and verbal reports, we modeled PM as an iterative loop of five sustained and transient phases: intention maintenance before target detection (TD), TD, intention maintenance after TD, action, and switching, the latter representing the activation of a new intention in mind. The fMRI analyses revealed continuous engagement of a top-down fronto-parietal network throughout the entire task, likely subserving goal maintenance in mind. In addition, a shift was observed from a perceptual (occipital) system while searching for places to go, to a mnemonic (temporo-parietal, fronto-hippocampal) system for remembering what actions to perform after TD. Updating of the top-down fronto-parietal network occurred at both TD and switching, the latter likely also being characterized by frontopolar activity.

    CONCLUSION/SIGNIFICANCE: Taken together, these findings show how brain systems complementary interact during real-world PM, and support a more complete model of PM that can be applied to naturalistic PM tasks and that we named PROspective MEmory DYnamic (PROMEDY) model because of its dynamics on both multi-phase iteration and the interactions of distinct neurocognitive networks.

  • 76.
    Kanli, Georgia
    Stockholm University, Faculty of Science, Department of Physics.
    Method for the classification of brain cancer treatment's responsiveness via physical parameters of DCE-MRI data2015Independent thesis Advanced level (degree of Master (Two Years)), 40 credits / 60 HE creditsStudent thesis
    Abstract [en]

    Tumors have several important hallmarks; anomalous and heterogeneous behaviors of their vascular structures, and high angiogenesis and neovascularization. Tumor tissue presents high blood flow (F) and extraction ratio (E) of contrast molecules. Consequently there is growing interest in non invasive methods for characterizing changes in tumor vasculature. Toft's model has been extensively used in the past in order to calculate Ktrans maps which take into consideration both F and E. However, in this thesis we argue that for accurate tumor characterization we need a model able to compute both F and E in tissue plasma.

    This project has been developed as part of a larger project, working toward building a Clinical Decision Support System (CDSS): an interactive expert computer software, that helps doctors and other health professionals make decisions regarding patient treatment progress. Using the Gamma Capillary Transit Time (GCTT) pharmacokinetic model we calculate F and E separately in a more realistic framework; unlike other models it takes into account the heterogeneity of the tumor, which depends on parameter a-1. a-1 is the width of the distribution of the capillary transit times within a tissue voxel. In more detail, a-1 expresses the heterogeneity of tissue microcirculation and microvasculature.

    We studied 9 patients pathologically diagnosed with glioblastoma multiforme (GBM), a common malignant type of brain tumor. Several physiological parameters including the blood flow and extraction ratio distributions were calculated for each patient. Then we investigated if these parameters can characterize early the patients' responsiveness to current treatment; we assessed the classification potential based on the actual therapy outcome. To this end, we present a novel analysis framework which exploits the new parameter a-1 and organizes each voxel into four sub-region. Our results indicate that early characterization of response based on GCCT can be significantly improved by focusing on tumor voxels from a specific sub-region.

  • 77.
    Karlsson, Kristin
    Stockholm University, Faculty of Science, Medical Radiation Physics (together with KI).
    Centrally located lung tumours treated with stereotactic body radiation therapy.2006Independent thesis Basic level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Background: This is a retrospective study of patients treated with stereotactic body radiation therapy (SBRT) with the stereotactic body frame for centrally located lung tumours. The purpose was to investigate the doses to the different structures of the tracheobronchial tree and to relate these doses to the incidence of atelectasis. The goal was to estimate a tolerance dose for the bronchi. Materials: The patient material consisted of 71 patient treated at the Karolinska University Hospital for a total of 102 tumours between November 1993 and March 2004. The patient group consisted of 36 men and 35 women with a mean age at the treatment of 67 years (range 34-87). The group was a mixture of patients with primary lung cancer and pulmonary metastases. Methods: After rereading and reactivating the dose plans for the patients in the treatment planning system (TPS) the different tracheobronchial structures (trachea, right mainstem bronchus, right superior bronchus, right intermedius bronchus, right medius bronchus, right inferior bronchus, left mainstem bronchus, left superior bronchus, left intermedius bronchus, left inferior bronchus) were outlined. The dose distribution in each structure was calculated and a dose-volume histogram (DVH) was created. Patients were allocated to four groups, i.e. patients with right sided tumours (22), left sided tumours (14), mediastinal tumours (23) and bilateral tumours (10). After that the maximum and mean doses to all structures were analysed. An oncologist reviewed the medical records for the patients and especially looked for atelectasis. The doses were related to the incidence of atelectasis.

    Results and Conclusions: For the patient group with right sided tumours it seems like the maximum doses to the bronchi are higher for the patients with atelectasis in comparison with patients without atelectasis. A better correlation between atelectasis and maximum doses rather than mean doses was observed for these patients. At this moment the results are too preliminary, so it is not possible to suggest a tolerance dose for the bronchi. What can be said is that the maximum doses to the bronchi for patients with right sided tumours without atelectasis are below 250 Gy3 expressed in biologically equivalent dose (BED) with α/β=3Gy, while at least one bronchi structure in the atelectasis patients received a maximum dose above 250 Gy3.

  • 78. Karlsson, Kristin
    et al.
    Nyman, Jan
    Baumann, Pia
    Wersall, Peter
    Drugge, Ninni
    Gagliardi, Giovanna
    Johansson, Karl-Axel
    Persson, Jan-Olov
    Stockholm University, Faculty of Science, Department of Mathematics.
    Rutkowska, Eva
    Tullgren, Owe
    Lax, Ingmar
    Retrospective Cohort Study of Bronchial Doses and Radiation-Induced Atelectasis After Stereotactic Body Radiation Therapy of Lung Tumors Located Close to the Bronchial Tree2013In: International Journal of Radiation Oncology, Biology, Physics, ISSN 0360-3016, E-ISSN 1879-355X, Vol. 87, no 3, p. 590-595Article in journal (Refereed)
    Abstract [en]

    Purpose: To evaluate the dose-response relationship between radiation-induced atelectasis after stereotactic body radiation therapy (SBRT) and bronchial dose. Methods and Materials: Seventy-four patients treated with SBRT for tumors close to main, lobar, or segmental bronchi were selected. The association between incidence of atelectasis and bronchial dose parameters (maximum point-dose and minimum dose to the high-dose bronchial volume [ranging from 0.1 cm(3) up to 2.0 cm(3)]) was statistically evaluated with survival analysis models. Results: Prescribed doses varied between 4 and 20 Gy per fraction in 2-5 fractions. Eighteen patients (24.3%) developed atelectasis considered to be radiation-induced. Statistical analysis showed a significant correlation between the incidence of radiation-induced atelectasis and minimum dose to the high-dose bronchial volumes, of which 0.1 cm(3) (D-0.1cm3) was used for further analysis. The median value of D-0.1cm3 (alpha/beta = 3 Gy) was EQD(2,LQ) = 147 Gy(3) (range, 20-293 Gy(3)). For patients who developed atelectasis the median value was EQD(2,LQ) = 210 Gy(3), and for patients who did not develop atelectasis, EQD(2,LQ) = 105 Gy(3). Median time from treatment to development of atelectasis was 8.0 months (range, 1.1-30.1 months). Conclusion: In this retrospective study a significant dose-response relationship between the incidence of atelectasis and the dose to the high-dose volume of the bronchi is shown.

  • 79. Kauppi, Karolina
    et al.
    Nilsson, Lars-Göran
    Stockholm University, Faculty of Social Sciences, Department of Psychology. Stockholm Brain Institute, Sweden.
    Persson, Jonas
    Stockholm University, Faculty of Social Sciences, Aging Research Center (ARC), (together with KI).
    Nyberg, Lars
    Additive genetic effect of APOE and BDNF on hippocampus activity2014In: NeuroImage, ISSN 1053-8119, E-ISSN 1095-9572, Vol. 89, p. 306-313Article in journal (Refereed)
    Abstract [en]

    Human memory is a highly heritable polygenic trait with complex inheritance patterns. To study the genetics of memory and memory-related diseases, hippocampal functioning has served as an intermediate phenotype. The importance of investigating gene-gene effects on complex phenotypes has been emphasized, but most imaging studies still focus on single polymorphisms. APOE epsilon 4 and BDNF Met, two of the most studied gene variants for variability in memory performance and neuropsychiatric disorders, have both separately been related to poorer episodic memory and altered hippocampal functioning. Here, we investigated the combined effect of APOE and BDNF on hippocampal activation (N = 151). No non-additive interaction effects were seen. Instead, the results revealed decreased activation in bilateral hippocampus and parahippocampus as a function of the number of APOE e4 and.BDNE Met alleles present (neither, one, or both). The combined effect was stronger than either of the individual effects, and both gene variables explained significant proportions of variance in BOLD signal change. Thus, there was an additive gene-gene effect of APOE and BDNF on medial temporal lobe (MTL) activation, showing that a larger proportion of variance in brain activation attributed to genetics can be explained by considering more than one gene variant This effect might be relevant for the understanding of normal variability in memory function as well as memory-related disorders associated with APOE and BDNF.

  • 80.
    Kramar, Johanna
    Stockholm University, Faculty of Science, Medical Radiation Physics (together with KI).
    Prostate brachytherapy: Pre-plan and real-time transperineal ultrasound guided Iodine-125 permanent seed implants at Södersjukhuset, Karolinska University Hospital.2008Independent thesis Basic level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Purpose: The aim of this thesis is to study the European (ESTRO/EAU/EORTC) and American (ABS) guidelines how to report the permanent seed implant and the most significant dosimetric parameters. It will also report on the permanent seed implant at Södersjukhuset, Karolinska University Hospital according to the guidelines. A large number of studies on pre- and post-implant dosimetry on permanent seed implants have recently been published but none is considered a standard. This makes it difficult, if not impossible, to compare data from different centres. The differences in reporting will also be discussed in this thesis. Another part of the study is to investigate how the morbidity correlates with the dose. The results in this report will give an overview of the experience at Södersjukhuset.

    Matherials and Methods: This study includes 198 patients who received implants between 2004-2007 with I-125 seeds under transperineal ultrasound at Södersjukhuset (to a prescribed dose of 145 Gy). The dose-planning system VariSeed 7.1 was used with an online connection to the ultrasound system with real-time verification. Dose constraints for the planning system are V(100)>99%, V(150)>60%, V(200)>25%, UrD(10)<130% and UrD(30)<125%. Outer and inner wall of rectum was outlined for 55 patients as recommended by ESTRO/EAU/EORTC and doses to rectum were also computed.

    Results: The median value for dosimetric parameters at Södersjukhuset, Karolinska University Hospital are for the prostate; D(90)=174Gy (153-194Gy), V(100)= 99% (93-100%), V(150)= 57% (40-74%), for the urethra; UrD(30) = 130% (112-147%), UrD(10) = 124% (107-142%) and for the rectum; RD2cc= 98Gy (73-128Gy), RD0.1cc=164Gy (119-240Gy), RV(100)=0.3cc (0.0-1.3cc), RV(150)=0.0cc (0.0-0.2cc). These values correspond to recommended data, except for the V(150) value. Regarding the clinically observed results, 3 patients had a relapse in their cancer, 2 patients had mild proctitis and 15 patients had urinary problems.

    Discussion and Conclusions: The significant dosimetric parameters for reporting according to ESTRO/EAU/EORTC and ABS for prostate are D90[Gy], V(100)[%] and V(150)[%], for urethra are D(30) and D(10), and for rectum RD2cc and RD0.1cc. These parameters consider as a minimum to use and they further recommend secondary parameters to report. Other authors have also recommended to report RV(100) and RV(150) for rectum. This study did not show any relationship between UrD(10), UrD(30) and urinary morbidity. According to the recommendations every patient should undergo a CT-based evaluation. Further investigations are needed on whether a post-implant CT-study is necessary for real-time implantation, as there is not enough published data on this aspect.

  • 81. Krzempek, D.
    et al.
    Mianowska, G.
    Bassler, Niels
    Stockholm University, Faculty of Science, Department of Physics.
    Stolarczyk, L.
    Kopeć, R.
    Sas-Korczyńska, B.
    Olko, P.
    CALIBRATION OF GAFCHROMIC EBT3 FILM FOR DOSIMETRY OF SCANNING PROTON PENCIL BEAM (PBS)2018In: Radiation Protection Dosimetry, ISSN 0144-8420, E-ISSN 1742-3406, Vol. 180, no 1-4, p. 324-328Article in journal (Refereed)
    Abstract [en]

    Gafchromic EBT3 films are applied in proton radiotherapy for 2D dose mapping because they demonstrate spatial resolution well below 1mm. However, the film response must be corrected in order to reach the accuracy of dose measurements required for the clinical use. The in-house developed AnalyseGafchromic software allows to analyze and correct the measured response using triple channel dose calibration, statistical scan-to-scan fluctuations as well as experimentally determined dose and LET dependence. Finally, the optimized protocol for evaluation of response of Gafchromic EBT3 films was applied to determine 30 x 40 cm(2) dose profiles of the scanning therapy unit at the Cyclotron Centre Bronowice, CCB in Krakow, Poland.

  • 82. Kulka, U.
    et al.
    Wojcik, Andrzej
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Di Giorgio, M.
    Wilkins, R.
    Suto, Y.
    Jang, S.
    Quing-Jie, L.
    Jiaxiang, L.
    Ainsbury, E.
    Woda, C.
    Roy, L.
    Li, C.
    Lloyd, D.
    Carr, Z.
    BIODOSIMETRY AND BIODOSIMETRY NETWORKS FOR MANAGING RADIATION EMERGENCY2018In: Radiation Protection Dosimetry, ISSN 0144-8420, E-ISSN 1742-3406, Vol. 182, no 1, p. 128-138Article in journal (Refereed)
    Abstract [en]

    Biological dosimetry enables individual dose reconstruction in the case of unclear or inconsistent radiation exposure situations, especially when a direct measurement of ionizing radiation is not or is no longer possible. To be prepared for large-scale radiological incidents, networking between well-trained laboratories has been identified as a useful approach for provision of the fast and trustworthy dose assessments needed in such circumstances. To this end, various biodosimetry laboratories worldwide have joined forces and set up regional and/or nationwide networks either on a formal or informal basis. Many of these laboratories are also a part of global networks such as those organized by World Health Organization, International Atomic Energy Agency or Global Health Security Initiative. In the present report, biodosimetry networks from different parts of the world are presented, and the partners, activities and cooperation actions are detailed. Moreover, guidance for situational application of tools used for individual dosimetry is given.

  • 83. Kulka, Ulrike
    et al.
    Abend, Michael
    Ainsbury, Elizabeth
    Badie, Christophe
    Francesc Barquinero, Joan
    Barrios, Lleonard
    Beinke, Christina
    Bortolin, Emanuela
    Cucu, Alexandra
    De Amicis, Andrea
    Dominguez, Inmaculada
    Fattibene, Paola
    Frovig, Anne Marie
    Gregoire, Eric
    Guogyte, Kamile
    Hadjidekova, Valeria
    Jaworska, Alicja
    Kriehuber, Ralf
    Lindholm, Carita
    Lloyd, David
    Lumniczky, Katalin
    Lyng, Fiona
    Meschini, Roberta
    Moertl, Simone
    Della Monaca, Sara
    Gil, Octavia Monteiro
    Montoro, Alegria
    Moquet, Jayne
    Moren, Mercedes
    Oestreicher, Ursula
    Palitti, Fabrizio
    Pantelias, Gabriel
    Patrono, Clarice
    Piqueret-Stephan, Laure
    Port, Matthias
    Jesus Prieto, Maria
    Quintens, Roel
    Ricoul, Michelle
    Romm, Horst
    Roy, Laurence
    Safrany, Geza
    Sabatier, Laure
    Sebastia, Natividad
    Sommer, Sylwester
    Terzoudi, Georgia
    Testa, Antonella
    Thierens, Hubert
    Turai, Istvan
    Trompier, Francois
    Valente, Marco
    Vaz, Pedro
    Voisin, Philippe
    Vral, Anne
    Woda, Clemens
    Zafiropoulos, Demetre
    Wojcik, Andrzej
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    RENEB - Running the European Network of biological dosimetry and physical retrospective dosimetry2017In: International Journal of Radiation Biology, ISSN 0955-3002, E-ISSN 1362-3095, Vol. 93, no 1, p. 2-14Article in journal (Refereed)
    Abstract [en]

    Purpose: A European network was initiated in 2012 by 23 partners from 16 European countries with the aim to significantly increase individualized dose reconstruction in case of large-scale radiological emergency scenarios. Results: The network was built on three complementary pillars: (1) an operational basis with seven biological and physical dosimetric assays in ready-to-use mode, (2) a basis for education, training and quality assurance, and (3) a basis for further network development regarding new techniques and members. Techniques for individual dose estimation based on biological samples and/or inert personalized devices as mobile phones or smart phones were optimized to support rapid categorization of many potential victims according to the received dose to the blood or personal devices. Communication and cross-border collaboration were also standardized. To assure long-term sustainability of the network, cooperation with national and international emergency preparedness organizations was initiated and links to radiation protection and research platforms have been developed. A legal framework, based on a Memorandum of Understanding, was established and signed by 27 organizations by the end of 2015. Conclusions: RENEB is a European Network of biological and physical-retrospective dosimetry, with the capacity and capability to perform large-scale rapid individualized dose estimation. Specialized to handle large numbers of samples, RENEB is able to contribute to radiological emergency preparedness and wider large-scale research projects.

  • 84.
    Kyllönen, J
    et al.
    Stockholm University, Faculty of Science, Medical Radiation Physics (together with KI).
    Lindborg, L
    Photon and neutron dose discrimination using low pressure proportional counters with graphite and A150 walls2007In: Radiation Protection Dosimetry, ISSN 0144-8420, Vol. 125, no 1-4, p. 314-317Article in journal (Refereed)
    Abstract [en]

    A graphite-walled proportional counter with low neutron sensitivity was used in combination with a tissue-equivalent proportional counter (TEPC) to separate the photon and neutron components in mixed radiation fields. Monte Carlo (MCNP4C) simulations of the photon and neutron responses of the two detectors were done to obtain correction factors for the sensitivity differences. In an alternative method the radiation components were determined using constant-yD-values for typical photon and neutron energy distributions. The results show no significant difference between the two methods and the measured neutron dose-equivalent agrees within ±50% with Bonner sphere determined values. The experimental data were obtained in measurement campaigns organised within the EVIDOS-project.

  • 85.
    Lannes, Itembu
    Stockholm University, Faculty of Science, Medical Radiation Physics (together with KI).
    Empirical measurements to ensure compliance with post therapy dose constraints to family members of radioiodine therapy patients2007Independent thesis Basic level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Radioiodine has been used in nuclear medicine for the treatment of thyroid diseases such as Thyroid Cancer and Thyrotoxicosis for many years. The treatment renders the patient radioactive. To minimize the dose to the patients’ relatives and the general public, restric-tions are imposed on the behaviour of the patient. This project presents the person dose equivalents actually received by family members of radioiodine patients following such restrictions. The family members wore hospital ID-bands on left and right wrists for up to four weeks. Each ID-band contained two LiF: Mg, Ti Thermo Luminescence Dosimeters (TLD) calibrated to measure air kerma. The TLDs were analysed and a total person dose equivalent received by the relative was calculated from the measured air kerma values. The results were compared to the dose constraints imposed by The Swedish Radiation Protection Authority (SSI FS 2000:3) in order to confirm that the new set of restrictions used at Karolinska University Hospital Huddinge maintains the dose to family members below the applicable limits.

    A total number of 22 relatives were recruited, 8 elderly, 7 adults and 7 children. Of the recruited relatives 4 (2 adults, 2 children) were excluded from the study as they had lost their dosimeter ID-bands or had other reasons not to participate in the study. This leaves the number of relatives used for data analysis at 18 individuals (8 elderly, 5 adults and 5 children) with a min age of 10 years and max age of 80 years.

    The observed average person dose equivalent of 0.43 mSv (max, 1.27; min, 0.12) indi-cates that the new method of individualised restriction used at Karolinska University Hospital Huddinge work as desired in keeping the dose to family members at an accept-able level. The accuracy of the clinical study has been shown to depend greatly on the method by which the dose is investigated but also on the properties of the TLD material used. There is a potential underestimation of air kerma due to fading of up to 30 %. In addition there are contributing uncertainties from both the calibration method and the conversion to person dose equivalent with the combined uncertainty estimated to be 14%.

  • 86.
    Larsson, Ylva
    Stockholm University, Faculty of Science, Medical Radiation Physics (together with KI).
    Establishing low-energy x-ray fields and determining operational dose equivalent conversion coefficients2008Independent thesis Basic level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Reference radiation fields for x-ray qualities are described by the International Organization of Standards (ISO). This study describes the procedure to establish nine different low energy X-ray qualities at the national metrology laboratory, Swedish Radiation Protection Authority, following the document ISO 4037. Measurements of tube voltage, half-value layer, mean energy and spectral resolution have been performed for qualities N-15, N-20, N-25, N-30, N-40, L-20, L-30, L-35 and L-55. Furthermore, dose equivalent conversion coefficients for operational quantities ambient dose equivalent, personal dose equivalent and directional dose equivalent have been calculated by folding the mono-energetic conversion factors with measured spectral distributions of the x-ray qualities. The spectral distributions were unfolded from pulse-height distributions to photon distributions using simulated data of the semi-conductor detector used for measurements, generated with the Monte Carlo code PENELOPE.

  • 87. Lavdas, Eleftherios
    et al.
    Mavroidis, Panayiotis
    Stockholm University, Faculty of Science, Department of Physics.
    Hatzigeorgiou, Vasiliki
    Roka, Violeta
    Arikidis, Nikos
    Oikonomou, Georgia
    Andrianopoulos, Konstantinos
    Notaras, Ioannis
    Elimination of motion and pulsation artifacts using BLADE sequences in knee MR imaging2012In: Magnetic Resonance Imaging, ISSN 0730-725X, E-ISSN 1873-5894, Vol. 30, no 8, p. 1099-1110Article in journal (Refereed)
    Abstract [en]

    The purpose of this study is to evaluate the ability of proton density (PD)-BLADE sequences in reducing or even eliminating motion and pulsatile flow artifacts in knee magnetic resonance imaging examinations. Eighty consecutive patients, who had been routinely scanned for knee examination, participated in the study. The following pairs of sequences with and without BLADE were compared: (a) PD turbo spin echo (TSE) sagittal (SAG) fat saturation (FS) in 35 patients, (b) PD TSE coronal (CUR) FS in 19 patients, (c) T2 TSE axial in 13 patients and (d) PD TSE SAG in 13 patients. Both qualitative and quantitative analyses were performed based on the signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) and relative contrast (ReCon) measures of normal anatomic structures. The qualitative analysis was performed by experienced radiologists. Also, the presence of image motion and pulsation artifacts was evaluated. Based on the results of the SNR, CRN and ReCon for the different sequences and anatomical structures, the BLADE sequences were significantly superior in 19 cases, whereas the corresponding conventional sequences were significantly superior in only 6 cases. BLADE sequences eliminated motion artifacts in all the cases. However, motion artifacts were shown in (a) six PD TSE SAG FS, (b) three PD TSE CUR FS, (c) three PD TSE SAG and (d) two T2 TSE axial conventional sequences. In our results, it was found that, in PD FS sequences (sagittal and coronal), the differences between the BLADE and conventional sequences regarding the elimination of motion and pulsatile flow artifacts were statistically significant. In all the comparisons, the PD FS BLADE sequences (coronal and sagittal) were significantly superior to the corresponding conventional sequences regarding the classification of their image quality. In conclusion, this technique appears to be capable to potentially eliminate motion and pulsatile flow artifacts in MR images.

  • 88. Lavdas, Eleftherios
    et al.
    Mavroidis, Panayiotis
    Stockholm University, Faculty of Science, Department of Physics. Karolinska Institutet.
    Kostopoulos, Spiros
    Glotsos, Dimitrios
    Roka, Violeta
    Koutsiaris, Aristotle G.
    Batsikas, Georgios
    Sakkas, Georgios K.
    Tsagkalis, Antonios
    Notaras, Ioannis
    Stathakis, Sotirios
    Papanikolaou, Nikos
    Vassiou, Katerina
    Elimination of motion, pulsatile flow and cross-talk artifacts using blade sequences in lumbar spine MR imaging2013In: Magnetic Resonance Imaging, ISSN 0730-725X, E-ISSN 1873-5894, Vol. 31, no 6, p. 882-890Article in journal (Refereed)
    Abstract [en]

    The purpose of this study is to evaluate the ability of T2 turbo spin echo (TSE) axial and sagittal BLADE sequences in reducing or even eliminating motion, pulsatile flow and cross-talk artifacts in lumbar spine MRI examinations. Forty four patients, who had routinely undergone a lumbar spine examination, participated in the study. The following pairs of sequences with and without BLADE were compared: a) 12 TSE Sagittal (SAG) in thirty two cases, and b) 12 TSE Axial (AX) also in thirty two cases. Both quantitative and qualitative analyses were performed based on measurements in different normal anatomical structures and examination of seven characteristics, respectively. The qualitative analysis was performed by experienced radiologists. Also, the presence of image motion, pulsatile flow and cross-talk artifacts was evaluated. Based on the results of the qualitative analysis for the different sequences and anatomical structures, the BLADE sequences were found to be significantly superior to the conventional ones in all the cases. The BLADE sequences eliminated the motion artifacts in all the cases. In our results, it was found that in the examined sequences (sagittal and axial) the differences between the BLADE and conventional sequences regarding the elimination of motion, pulsatile flow and cross-talk artifacts were statistically significant. In all the comparisons, the 12 TSE BLADE sequences were significantly superior to the corresponding conventional sequences regarding the classification of their image quality. In conclusion, this technique appears to be capable of potentially eliminating motion, pulsatile flow and cross-talk artifacts in lumbar spine MR images and producing high quality images in collaborative and non-collaborative patients.

  • 89. Lavdas, Eleftherios
    et al.
    Mavroidis, Panayiotis
    Stockholm University, Faculty of Science, Department of Physics.
    Kostopoulos, Spiros
    Glotsos, Dimitrios
    Roka, Violeta
    Topalzikis, Theofilos
    Bakas, Athanasios
    Oikonomou, Georgia
    Papanikolaou, Nikos
    Batsikas, Georgios
    Kaffes, Ioannis
    Kechagias, Dimitrios
    Improvement of image quality using BLADE sequences in brain MR imaging2013In: Magnetic Resonance Imaging, ISSN 0730-725X, E-ISSN 1873-5894, Vol. 31, no 2, p. 189-200Article in journal (Refereed)
    Abstract [en]

    The purpose of this study is to compare two types of sequences in brain magnetic resonance (MR) examinations of uncooperative and cooperative patients. For each group of patients, the pairs of sequences that were compared were two T2-weighted (T2-W) fluid attenuated inversion recovery sequences with different k-space trajectories (conventional Cartesian and BLADE) and two T2-TSE weighted with different k-space trajectories (conventional Cartesian and BLADE). Twenty-three consecutive uncooperative patients and 44 cooperative patients, who routinely underwent brain MR imaging examination, participated in the study. Both qualitative and quantitative analyses were performed based on the signal-to-noise ratio, contrast-to-noise ratio (CNR), and relative contrast (ReCon) measures of normal anatomic structures. The qualitative analysis was performed by experienced radiologists. Also, the presence of motion, other (e.g., Gibbs, susceptibility artifacts, phase encoding from vessels) artifacts and pulsatile flow artifacts was evaluated. In the uncooperative group of patients, BLADE sequences were superior to the corresponding conventional sequences in all the cases. Furthermore, the differences were found to be statistically significant in almost all the cases. In the cooperative group of patients, BLADE sequences were superior to the conventional sequences with the differences of the CNR and ReCon values in nine cases being statistically significant. Furthermore, BLADE sequences eliminated motion and other artifacts and T2 FLAIR BLADE sequences eliminated pulsatile flow artifacts. BLADE sequences (T2-TSE and T2 FLAIR) should be used in brain MR examinations of uncooperative patients. In cooperative patients, T2-TSE BLADE sequences may be used as part of the routine protocol and orbital examinations. T2 FLAIR BLADE sequences may be used optionally in examinations of AVM, orbits, haemorrhages, ventricular lesions, lesions in the frontal lobe, periventricular lesions, lesions in regions close to artifacts and lesions in posterior fossa.

  • 90. Lavdas, Eleftherios
    et al.
    Mavroidis, Panayiotis
    Stockholm University, Faculty of Science, Department of Physics.
    Topaltzikis, Theofilos
    Slatinopoulos, Vasileios
    Roka, Violeta
    Vlachopoulou, Anna
    Papanikolaou, Nikos
    Stathakis, Sotirios
    Kapsalaki, Eftichia
    Batsikas, Georgios
    Comparison of BLADE and conventional T2-TSE sequences for the sagittal visualization of the cervical spinal cord in multiple sclerosis patients - A case report2013In: Magnetic Resonance Imaging, ISSN 0730-725X, E-ISSN 1873-5894, Vol. 31, no 10, p. 1766-1770Article in journal (Refereed)
    Abstract [en]

    The purpose of this study is to report the significant differences found in the identification of lesions in cervical spinal cord of two patients with multiple sclerosis when using the BLADE T2-TSE and BLADE T2-TIRM sequences as opposed to the conventional T2-TSE and T2-TIRM sequences for sagittal acquisition at 1.5 T. In both patients, one more lesion was identified with the BLADE sequences than with the conventional ones. Consequently, we suggest the use of BLADE T2-TSE and BLADE T2-TIRM sequences in place of conventional ones for sagittal examination of the cervical spinal cord of multiple sclerosis patients. The advantages of TIRM to reveal the pathology of the cervical spinal cord and the advantage of BLADE sequences to improve image quality should be combined in a sequence that could be ideal for cervical spinal cord examinations.

  • 91.
    Lebedev, Alexander V.
    et al.
    Stockholm University, Faculty of Social Sciences, Aging Research Center (ARC), (together with KI). Stavanger University Hospital, Norway.
    Lövdén, Martin
    Stockholm University, Faculty of Social Sciences, Aging Research Center (ARC), (together with KI).
    Rosenthal, Gidon
    Feilding, Amanda
    Nutt, David J.
    Carhart-Harris, Robin L.
    Finding the self by losing the self: Neural correlates of ego-dissolution under psilocybin2015In: Human Brain Mapping, ISSN 1065-9471, E-ISSN 1097-0193, Vol. 36, no 8, p. 3137-3153Article in journal (Refereed)
    Abstract [en]

    Ego-disturbances have been a topic in schizophrenia research since the earliest clinical descriptions of the disorder. Manifesting as a feeling that one's self, ego, or I is disintegrating or that the border between one's self and the external world is dissolving, ego-disintegration or dissolution is also an important feature of the psychedelic experience, such as is produced by psilocybin (a compound found in magic mushrooms). Fifteen healthy subjects took part in this placebo-controlled study. Twelve-minute functional MRI scans were acquired on two occasions: subjects received an intravenous infusion of saline on one occasion (placebo) and 2 mg psilocybin on the other. Twenty-two visual analogue scale ratings were completed soon after scanning and the first principal component of these, dominated by items referring to ego-dissolution, was used as a primary measure of interest in subsequent analyses. Employing methods of connectivity analysis and graph theory, an association was found between psilocybin-induced ego-dissolution and decreased functional connectivity between the medial temporal lobe and high-level cortical regions. Ego-dissolution was also associated with a disintegration of the salience network and reduced interhemispheric communication. Addressing baseline brain dynamics as a predictor of drug-response, individuals with lower diversity of executive network nodes were more likely to experience ego-dissolution under psilocybin. These results implicate MTL-cortical decoupling, decreased salience network integrity, and reduced inter-hemispheric communication in psilocybin-induced ego disturbance and suggest that the maintenance of selfor ego, as a perceptual phenomenon, may rest on the normal functioning of these systems. Hum Brain Mapp 36:3137-3153, 2015.

  • 92. Liamsuwan, Thiansin
    et al.
    Hultqvist, Martha
    Stockholm University, Faculty of Science, Department of Physics.
    Lindborg, Lennart
    Uehara, Shuzo
    Nikjoo, Hooshang
    Microdosimetry of proton and carbon ions2014In: Medical physics (Lancaster), ISSN 0094-2405, Vol. 41, no 8, p. 239-250Article in journal (Refereed)
    Abstract [en]

    Purpose: To investigate microdosimetry properties of 160 MeV/u protons and 290 MeV/u C-12 ion beams in small volumes of diameters 10-100 nm. Methods: Energy distributions of primary particles and nuclear fragments in the beams were calculated from simulations with the general purpose code SHIELD-HIT, while energy depositions by monoenergetic ions in nanometer volumes were obtained from the event-by-event Monte Carlo track structure ion code PITS99 coupled with the electron track structure code KURBUC. Results: The results are presented for frequencies of energy depositions in cylindrical targets of diameters 10-100 nm, dose distributions (y) over bar (D) in lineal energy y, and dose-mean lineal energies YD For monoenergetic ions, the hp was found to increase with an increasing target size for high-linear energy transfer (LET) ions, but decrease with an increasing target size for low-LET ions. Compared to the depth dose profile of the ion beams, the maximum of the hp depth profile for the 160 MeV proton beam was located at similar to 0.5 cm behind the Bragg peak maximum, while the PD peak of the 290 MeV/u C-12 beam coincided well with the peak of the absorbed dose profile. Differences between the (y) over bar (D) and dose-averaged linear energy transfer (LETD) were large in the proton beam for both target volumes studied, and in the C-12 beam for the 10 nm diameter cylindrical volumes. The (y) over bar (D) determined for 100 run diameter cylindrical volumes in the C-12 beam was approximately equal to the LETD. The contributions from secondary particles to the (y) over bar (D) of the beams are presented, including the contributions from secondary protons in the proton beam and from fragments with atomic number Z = 1-6 in the C-12 beam. Conclusions: The present investigation provides an insight into differences in energy depositions in subcellular-size volumes when irradiated by proton and carbon ion beams. The results are useful for characterizing ion beams of practical importance for biophysical modeling of radiation-induced DNA damage response and repair in the depth profiles of protons and carbon ions used in radiotherapy.

  • 93.
    Liljequist, David
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Liamsuwan, Thiansin
    Nikjoo, Hooshang
    Elastic scattering cross section models used for Monte Carlo simulation of electron tracks in media of biological and medical interest2012In: International Journal of Radiation Biology, ISSN 0955-3002, E-ISSN 1362-3095, Vol. 88, no 1-2, p. 29-37Article in journal (Refereed)
    Abstract [en]

    Purpose: Elastic scattering is important for the spatial distribution of electrons penetrating matter, and thus for the distribution of deposited energy and DNA damage. Scattering media of interest are in particular liquid and gaseous water and gaseous nitrogen. The former are used as surrogates for tissue and cell environments (since more than 70% of the cell consists of water), while cross section data for nitrogen have been scaled and used as input in Monte Carlo (MC) codes simulating scattering in biologically relevant media. A short review is given of electron elastic scattering cross section models used in a biological and medical context and their experimental and theoretical background.

    Conclusions: Adequate theories and models exist for calculating elastic electron scattering in gaseous nitrogen and gaseous water (i.e., by free molecules) down to electron energies well below 100 eV. However, elastic electron scattering in liquid water at such low energies is apparently uncertain and not well understood. Further studies in the case of liquid water are thus motivated due to its biological importance.

  • 94. Lillhök, J.
    et al.
    Persson, L.
    Andersen, C. E.
    Dasu, A.
    Ardenfors, Oscar
    Stockholm University, Faculty of Science, Department of Physics.
    RADIATION PROTECTION MEASUREMENTS WITH THE VARIANCE-COVARIANCE METHOD IN THE STRAY RADIATION FIELDS FROM PHOTON AND PROTON THERAPY FACILITIES2018In: Radiation Protection Dosimetry, ISSN 0144-8420, E-ISSN 1742-3406, Vol. 180, no 1-4, p. 338-341Article in journal (Refereed)
    Abstract [en]

    The microdosimetric variance-covariance method was used to study the stray radiation fields from the photon therapy facility at the Technical University of Denmark and the scanned proton therapy beam at the Skandion Clinic in Uppsala, Sweden. Two TEPCs were used to determine the absorbed dose, the dose-average lineal energy, the dose-average quality factor and the dose equivalent. The neutron component measured by the detectors at the proton beam was studied through Monte Carlo simulations using the code MCNP6. In the photon beam the stray absorbed dose ranged between 0.3 and 2.4 mu Gy per monitor unit, and the dose equivalent between 0.4 and 9 mu Sv per monitor unit, depending on beam energy and measurement position. In the proton beam the stray absorbed dose ranged between 3 and 135 mu Gy per prescribed Gy, depending on detector position and primary proton energy.

  • 95.
    Lillhök, Jan Erik
    Stockholm University, Faculty of Science, Medical Radiation Physics (together with KI).
    The microdosimetric variance-covariance method used for beam quality characterization in radiation protection and radiation therapy2007Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Radiation quality is described by the RBE (relative biological effectiveness) that varies with the ionizing ability of the radiation. Microdosimetric quantities describe distributions of energy imparted to small volumes and can be related to RBE. This has made microdosimetry a powerful tool for radiation quality determinations in both radiation protection and radiation therapy. The variance-covariance method determines the dose-average of the distributions and has traditionally been used with two detectors to correct for beam intensity variations. Methods to separate dose components in mixed radiation fields and to correct for beam variations using only one detector have been developed in this thesis. Quality factor relations have been optimized for different neutron energies, and a new algorithm that takes single energy deposition events from densely ionizing radiation into account has been formulated. The variance-covariance technique and the new methodology have been shown to work well in the cosmic radiation field onboard aircraft, in the mixed photon and neutron fields in the nuclear industry and in pulsed fields around accelerators.

    The method has also been used for radiation quality characterization in therapy beams. The biological damage is related to track-structure and ionization clusters and requires descriptions of the energy depositions in nanometre sized volumes. It was shown that both measurements and Monte Carlo simulation (condensed history and track-structure) are needed for a reliable nanodosimetric beam characterization. The combined experimental and simulated results indicate that the dose-mean of the energy imparted to an object in the nanometre region is related to the clinical RBE in neutron, proton and photon beams. The results suggest that the variance-covariance technique and the dose-average of the microdosimetric quantities could be well suited for describing radiation quality also in therapy beams.

  • 96. Lindborg, L.
    et al.
    Hultqvist, Martha
    Stockholm University, Faculty of Science, Department of Physics.
    Tedgren, A. Carlsson
    Nikjoo, H.
    Lineal energy and radiation quality in radiation therapy: model calculations and comparison with experiment2013In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 58, no 10, p. 3089-3105Article in journal (Refereed)
    Abstract [en]

    Microdosimetry is a recommended method for characterizing radiation quality in situations when the biological effectiveness under test is not well known. In such situations, the radiation beams are described by their lineal energy probability distributions. Results from radiobiological investigations in the beams are then used to establish response functions that relate the lineal energy to the relative biological effectiveness (RBE). In this paper we present the influence of the size of the simulated volume on the relation to the clinical RBE values (or weighting factors). A single event probability distribution of the lineal energy is approximated by its dose average lineal energy ((y) over bar (D)) which can be measured or calculated for volumes from a few micrometres down to a few nanometres. The clinical RBE values were approximated as the ratio of the alpha-values derived from the LQ-relation. Model calculations are presented and discussed for the SOBP of a C-12 ion (290 MeV u(-1)) and the reference Co-60 gamma therapy beam. Results were compared with those for a conventional x-ray therapy beam, a 290 MeV proton beam and a neutron therapy beam. It is concluded that for a simulated volume of about 10 nm, the alpha-ratio increases approximately linearly with the (y) over bar (D)-ratio for all the investigated beams. The correlation between y and alpha provides the evidence to characterize a radiation therapy beam by the lineal energy when, for instance, weighting factors are to be estimated.

  • 97.
    Lindskog, Maria
    Stockholm University, Faculty of Science, Medical Radiation Physics (together with KI).
    Clinical Investigations of Image Guided Radiation Therapy for Prostate Cancer with an On-Board Imager2008Independent thesis Basic level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The daily uncertainty concerning tumor localization is one of the major problems during the course of radiation therapy. Image guided-radiation therapy (IGRT) can be used to improve the localization and adjustment of the planning target volume. The aim of this work was to evaluate both the IGRT technique used for prostate cancer patients at the department of the Karolinska University Hospital and an alternative on-line adaptive radiation therapy (ART) method with an On-Board Imager (OBI).

    In the first part of the thesis 2D and 3D image registration with an OBI were compared. Ten prostate cancer patients were involved in the analyses. Two different statistical tests were used to determine significant systematic deviations between the two methods. The second part concerns daily dose verifications and dose plan reoptimization of one intensity modulated radiation therapy (IMRT) prostate cancer patient treated with IGRT. The study was based on cone-beam computed tomography (CBCT) images acquired at 6 different treatment fractions. The risk of developing late rectal and bladder toxicity was quantified using normal tissue complication probability (NTCP) calculations. Additional measurements on an Alderson phantom were performed to verify the accuracy of using the CBCT images for dose calculations.

    A statistically significant difference between the 2D-2D and the 3D-3D match applications could be observed in lateral and longitudinal direction. However, the effect differed among the patients. The phantom measurements showed small dose deviations between the CT and CBCT image, with a mean dose increase to the prostate and seminal vesicles (SV) of 2.5 %. The daily dose to the prostate and SV of the IMRT patient showed to be satisfactory. The daily dose to the rectum did not exceed the prescribed rectal dose except at one treatment fraction and the highest risk of developing late rectal toxicity was about 10.4 %. Large daily bladder dose variations were observed and at two treatment fractions the bladder dose restrictions were exceeded. With a reoptimization process of the dose plan, the dose to the bladder could be reduced while conserving the dose to the target.

    This work shows that for these specific patient cases appropriate doses to the prostate and SV can be delivered with IGRT. However, introducing a suitable ART method could lead to a reduction of inter-fractional rectal and bladder dose variations.

  • 98. Lisowska, Halina
    et al.
    Brehwens, Karl
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Zoelzer, Friedo
    Wegierek-Ciuk, Aneta
    Czub, Joanna
    Lankoff, Anna
    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. Jan Kochanowski University, Poland.
    Effect of hypothermia on radiation-induced micronuclei and delay of cell cycle progression in TK6 cells2014In: International Journal of Radiation Biology, ISSN 0955-3002, E-ISSN 1362-3095, Vol. 90, no 4, p. 318-324Article in journal (Refereed)
    Abstract [en]

    Purpose: Low temperature (hypothermia) during irradiation leads to a reduced frequency of micronuclei in TK6 cells and it has been suggested that perturbation of cell cycle progression is responsible for this effect. The aim of the study was to test this hypothesis. Materials and methods: Human lymphoblastoid TK6 cells were treated by a combination of hypothermia (0.8 degrees C) and ionizing radiation in varying order (hypothermia before, during or after irradiation) and micronuclei were scored. Growth assay and two-dimensional flow cytometry was used to analyze cell cycle kinetics following irradiated of cells at 0.8 degrees C or 37.0 degrees C. Results: The temperature effect was observed at the level of micronuclei regardless of whether cells were cooled during or immediately before or after the radiation exposure. No indication of cell cycle perturbation by combined exposure to hypothermia and radiation could be detected. Conclusions: The protective effect of hypothermia observed at the level of cytogenetic damage was not due to a modulation of cell cycle progression. A possible alternative mechanism and experiments to test it are discussed.

  • 99. Lisowska, Halina
    et al.
    Wegierek-Ciuk, Aneta
    Banasik-Nowak, Anna
    Braziewicz, Janusz
    Wojewodzka, Maria
    Wojcik, Andrzej
    Stockholm University, Faculty of Science, Department of Genetics, Microbiology and Toxicology.
    Lankoff, Anna
    The dose-response relationship for dicentric chromosomes and gamma-H2AX foci in human peripheral blood lymphocytes:  Influence of temperature during exposure and intra- and inter-individual variability of donors2013In: International Journal of Radiation Biology, ISSN 0955-3002, E-ISSN 1362-3095, Vol. 89, no 3, p. 191-199Article in journal (Refereed)
    Abstract [en]

    Purpose : Hypothermia during in vitro irradiation of human peripheral blood lymphocytes (PBL) affects the level of chromosome aberrations. The molecular mechanisms of this phenomenon are not fully understood. The aim of our study was to examine the effect of hypothermia on the dose-response relationship for dicentric chromosomes and the level of gamma-H2AX (phosphorylated histone H2AX) foci. In addition, the inter- and intra-individual variability was assessed in relation to temperature. Materials and methods : PBL were kept at 0.8, 20 and 37 degrees C and then exposed to gamma-rays (from 0-3 Gy). Dicentric chromosomes were scored in first post-treatment mitoses. gamma H2AX foci were scored 15, 30, 60, 120 min and 24 h post irradiation. Results : Our results revealed that the frequency of dicentric chromosomes in cells exposed at 37 degrees C to gamma-rays was higher than after exposure at 0.8 and 20 degrees C. No effect of temperature was observed on the number of gamma-H2AX foci as well as on the intra-and inter-individual variations of the dicentric yield and the number of gamma-H2AX foci. Conclusions : Temperature at exposure to ionizing radiation has a pronounced effect on the level of cytogenetic damage but not gamma-H2AX foci.

  • 100. Liu, Yawu
    et al.
    Spulber, Gabriela
    Lehtimäki, Kimmo K
    Könönen, Mervi
    Hallikainen, Ilona
    Gröhn, Heidi
    Kivipelto, Miia
    Stockholm University, Faculty of Social Sciences, Aging Research Center (ARC), (together with KI).
    Hallikainen, Merja
    Vanninen, Ritva
    Soininen, Hilkka
    Diffusion tensor imaging and tract-based spatial statistics in Alzheimer's disease and mild cognitive impairment2011In: Neurobiology of Aging, ISSN 0197-4580, E-ISSN 1558-1497, Vol. 32, no 9, p. 1558-1571Article in journal (Refereed)
    Abstract [en]

    We aimed to explore the changes in fractional anisotropy (FA) in subjects with mild cognitive impairment (MCI) and Alzheimer's disease (AD) by analyzing diffusion tensor imaging (DTI) data using the Tract-Based Spatial Statistics (TBSS). DTI data were collected from 17 AD patients, 27 MCI subjects and 19 healthy controls. Voxel-based analysis with TBSS was used to compare FA among the three groups. Additionally, guided by TBSS findings, a region of interest (ROI)-based analysis along the TBSS skeleton was performed on group-level and the accuracy of the method was assessed by the back-projection of ROIs to the native space FA. Neurofiber tracts with decreased FA included: the parahippocampal white matter, cingulum, uncinate fasciculus, inferior and superior longitudinal fasciculus, corpus callosum, fornix, tracts in brain stem, and cerebellar tracts. Quantitative ROI-analysis further demonstrated the significant decrease on FA values in AD patients relative to controls whereas FA values of MCI patients were found in between the controls and AD patients. We conclude that TBSS is a promising method in examining the degeneration of neurofiber tracts in MCI and AD patients.

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