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Development of an efficient scanning and purging magnet system for IMRT with narrow high energy photon beams
Stockholm University, Karolinska Intstitute.
Stockholms universitet, Naturvetenskapliga fakulteten, Manne Siegbahn-laboratoriet.
Vise andre og tillknytning
2009 (engelsk)Inngår i: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 612, nr 1, s. 201-208Artikkel i tidsskrift (Fagfellevurdert) 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.

sted, utgiver, år, opplag, sider
2009. Vol. 612, nr 1, s. 201-208
Emneord [en]
IMRT, Scanned beams, High energy photons, Electron contamination, Purging magnet
Forskningsprogram
medicinsk strålningsfysik
Identifikatorer
URN: urn:nbn:se:su:diva-45774DOI: 10.1016/j.nima.2009.10.062ISI: 000273101300022OAI: oai:DiVA.org:su-45774DiVA, id: diva2:369770
Tilgjengelig fra: 2010-11-11 Laget: 2010-11-11 Sist oppdatert: 2017-12-12bibliografisk kontrollert
Inngår i avhandling
1. Development of improved radiation therapy techniques using narrow scanned photon beams
Åpne denne publikasjonen i ny fane eller vindu >>Development of improved radiation therapy techniques using narrow scanned photon beams
2010 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
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.

sted, utgiver, år, opplag, sider
Stockholm: Department of Physics, Stockholm University, 2010. s. 36
Emneord
IMRT, Scanned photon beams, PET-CT treatment verification, Monte Carlo
HSV kategori
Forskningsprogram
medicinsk strålningsfysik
Identifikatorer
urn:nbn:se:su:diva-45809 (URN)978-91-7447-189-2 (ISBN)
Disputas
2010-12-10, Föreläsningssalen, Cancer Centrum Karolinska, R8:00, Karolinska universitetssjukhuset, Solna, 14:00 (engelsk)
Opponent
Veileder
Merknad
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Submitted. Paper 4: Submitted.Tilgjengelig fra: 2012-01-12 Laget: 2010-11-11 Sist oppdatert: 2012-01-12bibliografisk kontrollert

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