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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
Stockholm University, Faculty of Science, Department of Physics.
Karolinska Institute, Medical Radiation Physics.
Karolinska Institutet, Medical Radiation Physics.
(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.

URN: urn:nbn:se:su:diva-45796OAI: diva2:369779
Available from: 2010-11-11 Created: 2010-11-11 Last updated: 2012-01-12Bibliographically approved
In thesis
1. Development of improved radiation therapy techniques using narrow scanned photon beams
Open this publication in new window or tab >>Development of improved radiation therapy techniques using narrow scanned photon beams
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.
IMRT, Scanned photon beams, PET-CT treatment verification, Monte Carlo
National Category
Natural Sciences
Research subject
Medical Radiation Physics
urn:nbn:se:su:diva-45809 (URN)978-91-7447-189-2 (ISBN)
Public defence
2010-12-10, Föreläsningssalen, Cancer Centrum Karolinska, R8:00, Karolinska universitetssjukhuset, Solna, 14:00 (English)
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

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