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Thesis

English

ID: <

10670/1.4pa5r0

>

Where these data come from
Advancing the generation of proton minibeams for radiation therapy

Abstract

Despite major advances over the last decades, the dose tolerance of normal tissue continues to be a central problem in radiation therapy, limiting for example the effective treatment of hypoxic tumours and high-grade gliomas. Proton minibeam radiation therapy (pMBRT) is a novel therapeutic strategy, combining the improved ballistics of protons with the enhanced tissue sparing potential of submillimetric, spatially fractionated beams (minibeams), that has already demonstrated its ability to significantly improve the therapeutic index for brain cancers in rats. In contrast to conventional proton therapy which uses comparatively large beam diameters of five millimetres to several centimetres, minibeams require beam sizes of less than 1 mm which are challenging to create in a clinical context. So far, every implementation of pMBRT at clinically relevant beam energies could only be achieved with the help of mechanical collimators (metal blocks with thin slits or holes). However, this method is inefficient, inflexible and creates high levels of unwanted secondary particles. The optimal approach may therefore be the generation of minibeams through magnetic focussing.This thesis investigates how magnetically focussed proton minibeams can be realised in a clinical context. Starting from the computer model of a modern pencil beam scanning nozzle (the term "nozzle" describes the final elements of a clinical beamline), it could be shown that current nozzles will not be suitable for this task, since their large dimensions and the presence of too much air in the beam path make it impossible to focus the beam down to the required sizes. Instead, an optimised nozzle design has been developed and evaluated with clinical beam models. It could be demonstrated that this design allows the generation of proton minibeams through magnetic focussing and that the new nozzle can be used with already existing technology. Moreover, a Monte Carlo study was performed to compare and quantify the differences between magnetically focussed minibeams and mechanically collimated minibeams.Finally, as the second aspect of this thesis, helium ions were evaluated as a potential alternative to protons for minibeam radiation therapy. It could be shown that helium ions could present a good compromise exhibiting many of the dosimetric advantages of heavier ions without the risks related to normal tissue toxicities.

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