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Development of improved radiation therapy techniques using narrow scanned photon beams
Stockholm University, Faculty of Science, Department of Physics.
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The present thesis is focused on the development and application of narrow scanned high energy photon beam for radiation therapy. The introduction of physically and biologically optimized intensity modulated radiation therapy (IMRT) requires a flexible and accurate dose delivery method to maximize the treatment outcome. Narrow scanned photon beams is a fast option for IMRT since it is not dependent on mechanically moving heavy collimator leafs and largely independent of the complexity of the desired dose distribution. Scanned photon beams can be produced by scanning an electron beam of low emittance, incident on a thin bremsstrahlung target of low atomic number. The large fraction of high energy electrons that are transmitted through the target has to be removed by a strong purging magnet. In the thesis a strong purging magnet, coupled with a magnetic scanning magnet, is presented for an intrinsic electron energy of 50 - 75 MeV and a source to isocenter distance of 75 cm. The available scan area at isocenter can be as large as 43 x 40 cm2 for an incident electron energy of 50 MeV and 28 x 40 cm2 at 75 MeV.

By modifying the existing treatment head of the racetrack microtron MM50, it was possible to experimentally produce relevant dose distributions with interesting properties from 50 MV scanned narrow photon beams while deflecting the transmitted electrons onto a simplified electron stopper. The deflection of the transmitted electrons was studied both experimentally and by the Monte Carlo method. With high energy photons, treatment verification is possible through PET-CT imaging of the positron annihilations induced by photonuclear reactions in the patient. Narrow scanned high energy photon beams is the ideal beam quality since the activation efficiency and the effective photon energy will be more uniform than the filtered photon beam from a full range bremsstrahlung target.

The induced 11C activity 50 MV by scanned narrow photon beams was measured using PET-CT imaging and compared with Monte Carlo simulations. The combination of fast flexible dose delivery with treatment verification using PET-CT imaging makes narrow high energy scanned photon beams a very interesting treatment modality for biologically optimized adaptive radiation therapy.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University , 2010. , 36 p.
Keyword [en]
IMRT, Scanned photon beams, PET-CT treatment verification, Monte Carlo
National Category
Natural Sciences
Research subject
Medical Radiation Physics
Identifiers
URN: urn:nbn:se:su:diva-45809ISBN: 978-91-7447-189-2 (print)OAI: oai:DiVA.org:su-45809DiVA: diva2:369880
Public defence
2010-12-10, Föreläsningssalen, Cancer Centrum Karolinska, R8:00, Karolinska universitetssjukhuset, Solna, 14:00 (English)
Opponent
Supervisors
Note
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Submitted. Paper 4: Submitted.Available from: 2012-01-12 Created: 2010-11-11 Last updated: 2012-01-12Bibliographically approved
List of papers
1. Application of Geant4 in the development of new radiation therapy treatment methods
Open this publication in new window or tab >>Application of Geant4 in the development of new radiation therapy treatment methods
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2006 (English)In: Proceedings of the 9th Conference, Astroparticle, Particle and Space Physics, Detectors and Medical Physics Applications / [ed] Michele Barone, Emilio Borchi, Andrea Gaddi, claude Leroy, Larry Price, Pier-Giorgio Rancoita, Randal Ruchti, 5 Toh Tuck Link, singapore: World Scientific Publishing Co. Pte. Ltd. , 2006, 451-461 p.Conference paper, Published paper (Refereed)
Abstract [en]

There is a very fast development of new radiation treatment methods today, from advanced use of intensity modulated photon and electron beams to light ion therapy with narrow scanned beam based treatment units. Accurate radiation transport calculations are a key requisite for these developments where Geant4 is a very useful Monte Carlo code for accurate design of new treatment units. Today we cannot only image the tumor by PET-CT imaging before the treatment but also determine the tumor sensitivity to radiation and even measure in vivo the delivered absorbed dose in three dimensions in the patient. With such methods accurate Monte Carlo calculations will make radiation therapy an almost exact science where the curative doses can be calculated based on patient individual response data. In the present study results from the application of Geant4 are discussed and the comparisons between Geant4 and experimental and other Monte Carlo data are presented.

Place, publisher, year, edition, pages
5 Toh Tuck Link, singapore: World Scientific Publishing Co. Pte. Ltd., 2006
National Category
Natural Sciences
Research subject
Medical Radiation Physics
Identifiers
urn:nbn:se:su:diva-45776 (URN)981-256-798-4 (ISBN)
Conference
Astroparticle, Particle and Space Physics, detector and Medical Physics Applications
Available from: 2010-11-11 Created: 2010-11-11 Last updated: 2012-01-12Bibliographically approved
2. Development of an efficient scanning and purging magnet system for IMRT with narrow high energy photon beams
Open this publication in new window or tab >>Development of an efficient scanning and purging magnet system for IMRT with narrow high energy photon beams
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2009 (English)In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 612, no 1, 201-208 p.Article in journal (Refereed) Published
Abstract [en]

Due to the clinical advantages of Intensity Modulated Radiation Therapy (IMRT) high flexibility and accuracy in intensity modulated dose delivery is desirable to really maximize treatment outcome. Although it is possible to deliver IMRT by using broad beams in combination with dynamic multileaf collimation the process is rather time consuming and inefficient. By using narrow scanned high energy photon beams the treatment outcome can be improved, the treatment time reduced and accurate 3D in vivo dose delivery monitoring is possible by PET-CT based dose delivery imaging of photo nuclear reactions in human tissues. Narrow photon beams can be produced by directing a low emittance high energy electron beam on a thin target, and then cleaning the therapeutic photon beam from transmitted high energy electrons, and photon generated charged leptons, with a dedicated purging magnet placed directly downstream of the target. To have an effective scanning and purging magnet system the purging magnet should be placed immediately after the bremsstrahlung target to deflect the transmitted electrons to an efficient electron stopper. In the static electron stopper the electrons should be safely collected independent of the desired direction of the therapeutic scanned photon beam. The SID (Source to Isocentre Distance) should preferably be short while retaining the ability to scan over a large area on the patient and consequently there are severe requirements both on the strength and the geometry of the scanning and purging magnets. In the present study an efficient magnet configuration with a purging and scanning magnet assembly is developed for electron energies in the 50-75 MeV range and a SID of 75 cm. For a bremsstrahlung target of 3mm Be these electron energies produce a photon beam of 25-17 mm FWHM (Full Width Half Maximum) at a SID of 75 cm. The magnet system was examined both in terms of the efficiency in scanning the narrow bremsstrahlung beam and the deflection of transmitted and photon generated electrons. The simulations show that its is possible to have a scan area on the patient of up to 43 x 40 cm2 for an incident electron energy of 50 MeV and 28 x 40 cm2 at 75 MeV, while at the same time adequately deflecting the transmitted electron beam.

Keyword
IMRT, Scanned beams, High energy photons, Electron contamination, Purging magnet
Research subject
Medical Radiation Physics
Identifiers
urn:nbn:se:su:diva-45774 (URN)10.1016/j.nima.2009.10.062 (DOI)000273101300022 ()
Available from: 2010-11-11 Created: 2010-11-11 Last updated: 2017-12-12Bibliographically approved
3. Fast IMRT with narrow high energy scanned photon beams
Open this publication in new window or tab >>Fast IMRT with narrow high energy scanned photon beams
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2011 (English)In: Medical physics (Lancaster), ISSN 0094-2405, Vol. 38, no 8, 4774-4784 p.Article in journal (Refereed) Published
Abstract [en]

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

Keyword
IMRT, scanned photon beams, Monte Carlo
National Category
Radiology, Nuclear Medicine and Medical Imaging
Identifiers
urn:nbn:se:su:diva-69259 (URN)10.1118/1.3615059 (DOI)000293417500038 ()
Note
authorCount :5 Affiliation for 4 of the authors of the Stockholm University: Department of Medical Radiation Physics, Karolinska Institutet and Stockholm UniversityAvailable from: 2012-01-12 Created: 2012-01-11 Last updated: 2017-12-08Bibliographically approved
4. Development of a diagnostic treatment unit combining fast radiobiologically optimized adaptive IMRT with in vivo 3D dose delivery and tumor responsivness verification using PET-CT imaging
Open this publication in new window or tab >>Development of a diagnostic treatment unit combining fast radiobiologically optimized adaptive IMRT with in vivo 3D dose delivery and tumor responsivness verification using PET-CT imaging
(English)Article in journal (Other academic) Submitted
Abstract [en]

The novel radiation therapy unit described here is designed for fast and cost effective adaptive intensity modulated radiation therapy. Today, efficient tumor diagnostics based on PET-CT imaging, using tumor specific tracers, allow accurate delineation of the local regional tumor spread, both before the start of the treatment and during the first two weeks of treatment to quantify the treatment response. This type of image allows monitoring of the local radiation responsiveness of the tumor in 3D. Thus, the total delivered dose distribution can be optimally controlled by adapting the initial biologically optimized treatment plan based on the integrated dose delivery and biological response during fractionated radiation therapy. The biological adaptation can be based on the initial tumor spread, and also the observed in vivo tumor responsiveness to increase both the quality and safety of the treatment.

Fast high energy pencil beam scanning offers a possibility for intensity modulation in combination with online treatment verification by combining PET and radiotherapeutic-computed tomography (PET-RCT). It may even be possible to image the substantial quasi prompt positron annihilation induced between pulses through pair production by high energy photons in addition to the positrons generated by photonuclear reactions, to get a photon dose related signal that is almost independent on the vascular blood flow in the patient.

The fast narrow photon and electron pencil beam scanning system integrated with the new fast gea electron multiplier (GEM) portal imager and laser camer (LC) may also in the future allow improved patient set-up as well as dynamic locking on a moving tumor in real time. Interestingly, the beam scanning system can be auto-calibrated and use real time dosimetric verification with the segmented high-resolution transmission monitor. The new therapy system will thus be an ideal tool for true 3D IMRT.

Identifiers
urn:nbn:se:su:diva-45796 (URN)
Available from: 2010-11-11 Created: 2010-11-11 Last updated: 2012-01-12Bibliographically approved

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