Abstract
Purpose: Development of a versatile detector system primarily designed for online range monitoring of proton beams generated via the novel technique of particle acceleration from high‐power, short‐pulse lasers to be used in bio‐medical applications. Methods: While so far mostly offline diagnostics tools are used in this context, we aim at developing a technique based on the position‐sensitive detection of prompt gamma rays emitted from nuclear reactions between the proton beam and the biological sample. For this purpose, we develop a Compton camera capable to track not only the Compton scattered primary photon, but also the secondary Compton electron. Results: Extensive simulation studies resulted in an optimized design of the Compton camera based on a LaBr3(Ce) scintillation crystal (50×50×30 mm3 block crystal, read out by a multi‐anode PMT) acting as absorber, preceded by a stack of 6 double‐sided silicon strip detectors as scatterers (500 μm thick, 128 strips/side, pitch 390 μm). From the design simulations an angular resolution of <= 2° (at 2–6 MeV) and a source image reconstruction efficiency of 10−3 −10−3 (at 1–5 MeV) can be expected. The LaBr3 crystal has been characterized with laboratory sources, resulting in a time resolution of 540 ps and a position‐dependent energy resolution (best in the central region). Using a collimated source the point‐spread function was determined from the pixelated light distribution, yield a (preliminary and by software optimization improving) spatial resolution of < 3mm. Conclusion: The Compton camera based approach for prompt‐γ detection from nuclear interactions of therapeutic ion beams offers very promising perspectives for online range monitoring. An arrangement of several camera modules could even be used in a γ‐PET mode to additionally detect delayed annihilation radiation from positron emitters in the irradiation interrupts (with improved performance in the presence of an additional third (prompt) γ (as e.g. in 10C, 14O). Funding support via German Science Foundation: DFG Cluster of Excellence MAP (Munich Centre for Advanced Photonics)