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Radiobiological investigations of proton and light ion therapy
Stockholm University, Faculty of Science, Medical Radiation Physics (together with KI).
2002 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

During the last decade, the interest in proton and light ion beam therapy has increased considerably and several new centres are planned around the world. These particles have a large advantage due to their sharp physical dose distributions as compared to conventional radiotherapy beams. By magnetic scanning of the particle beam, full conformal dose delivery can be obtained. Protons and particularly light ions also have an enhanced relative biological effectiveness (RBE) that needs to be considered to optimise the biological effect in the tumour volume and to minimise the damage to normal tissues. The aim of this work is to investigate the many concurrent factors influencing the RBE of protons and light ions and to explore the influence of applying a variable RBE correction on a clinical proton treatment plan.

The different models available are tested regarded their ability to predict the outcome of cell survival experiments for mixed radiation qualities and a new experimental data set is produced for this purpose. The dependence of the parameters a and b of the linear quadratic (LQ) model on the linear energy transfer (LET) for protons is studied. It can be concluded that the increase in a with LET is the main reason for the increase in RBE with increasing LET. Furthermore, this increase tends to be higher for cells with a high capacity of repairing low-LET induced damage.

To improve the knowledge of the different factors influencing the RBE, the Monte Carlo code PENELOPE is modified and extended to enable simulations of secondary electron slowing down spectra generated by different radiation qualities. Based on the obtained spectra it is shown that the fluence of secondary electrons of low energies (~100 eV-1 keV), that have a high capacity to induce severe damage to the DNA, is increased for decreasing proton and light ion energies. The variation of the secondary electron slowing down spectrum together with the LET and energy variation of the K-shell ionisation cross sections, for electrons as well as ions, can have a significant influence on the biological response on the cellular level.

A novel solution for scanning of a proton beam with a moveable second magnet was implemented. It allows full conformal dose delivery with a maximum field size of 300 x 300 mm2 for a 200 MeV proton beam with a source-to-surface distance (SSD) of 1 m.

Methods for applying a variable RBE correction on a clinical proton treatment plan are developed. A significant difference, compared to the fixed RBE of 1.1 presently utilised at most centres, is obtained for normal tissues immediately behind the tumour target in the direction of the beam(s), indicating the importance of introducing such a variable correction for proton and light ion therapy planning. 

Place, publisher, year, edition, pages
Stockholm: Stockholm University , 2002. , 50 p.
Keyword [en]
Radiobiology, Monte Carlo method, Radiotherapy, high-energy instrumentation, Protons, Light ions, RBE, LET, Radiobiological models
Keyword [sv]
Radiobiologi
National Category
Biophysics Medical Biotechnology
Research subject
Medical Radiation Physics
Identifiers
URN: urn:nbn:se:su:diva-142859ISBN: 91-7265-416-3 (print)OAI: oai:DiVA.org:su-142859DiVA: diva2:1094884
Public defence
2002-04-19, 09:15 (English)
Opponent
Note

Härtill 4 uppsatser

Available from: 2017-05-11 Created: 2017-05-11 Last updated: 2017-09-27Bibliographically approved

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