Abstract
Prompt gamma (PG) based range verification can potentially reduce the safety margins in proton therapy. A knife-edge slit camera has been developed in this context using analytical PG simulations as reference for absolute range verification during patient treatment. Geometrical deviations between measurement and simulation could be observed and have to be corrected for in order to improve the range retrieval of the system. A geometrical correction model is derived from Monte Carlo simulations in water. The influence of different parameters is tested and the model is validated in a dedicated benchmark experiment. We found that the geometrical correction improves the agreement between measured and simulated PG profiles resulting in an improved range retrieval and higher accuracy for absolute range verification. An intrinsic offset of 1.4 mm between measurement and simulation is observed in the experimental data and corrected in the PG simulation. In summary, the absolute range verification capabilities of a PG camera have been improved by applying a geometrical correction model.
Highlights
The finite range of protons as well as the maximum ionization density close to their stopping point makes proton beam therapy a superior treatment modality for specific tumour locations compared to conventional radiotherapy based on photons
Prompt gamma rays (PGs), which are emitted in nuclear reactions between primary proton beam and tissue, are the ideal probe for range verification as they exhibit a strong correlation with the Instruments 2018, 2, 25; doi:10.3390/instruments2040025
The presence of the Bragg peak and the dose fall-off are resembled by a similar fall-off in the production of the PGs, whose shape depends on the nuclear reaction cross sections [5]
Summary
The finite range of protons as well as the maximum ionization density close to their stopping point makes proton beam therapy a superior treatment modality for specific tumour locations compared to conventional radiotherapy based on photons. Range uncertainties, coming from the planning phase (e.g., conversion of CT information to proton stopping power), patient movement and anatomical changes, have to be covered by safety margins of a few mm in clinical practice [1,2]. To reduce those margins and fully exploit the potential of protons, in-vivo range verification is highly desirable. Prompt gamma rays (PGs), which are emitted in nuclear reactions between primary proton beam and tissue, are the ideal probe for range verification as they exhibit a strong correlation with the Instruments 2018, 2, 25; doi:10.3390/instruments2040025 www.mdpi.com/journal/instruments. The detection of PGs requires specific detection devices due to their high energies between 1–8 MeV [6] and the high background coming from neutron-induced events
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