Helmholtz-Zentrum Dresden-Rossendorf (HZDR) Detection Systems for Range Monitoring in Proton Therapy: Needs and Challenges

12 In-vivo range verification has been a hot topic in particle therapy for about two decades. In spite of vast efforts made by 13 research groups all over the world, clinical devices and procedures for routinely monitoring the range of therapeutic particle 14 beams in the patient’s body and to ensure their correspondence with the treatment plan are not yet available. The paper 15 reviews recent approaches with focus on prompt-gamma based methods of proton range verification and points to challenges 16 that have not been discussed with the necessary depth and rigor in many (even recent) publications: First, the macro time 17 structure of treatment beams in common proton therapy facilities requires detection systems with extreme load tolerance, 18 throughput capability, and stability against load leaps. Second, the time period available for verifying the range of a single 19 pencil beam spot is of the order of milliseconds, which limits the number of prompt gamma events that can be detected and 20 processed. In view of these constraints it might be favorable to waive tight event selection by collimation or coincidence 21 conditions as applied in most prompt-gamma based range verification techniques considered so far, and to move on to straight 22 detection with uncollimated detectors combined with a multi-feature analysis deploying all pieces of information comprised in 23 a registered event. Energy deposition, timing, and energy sharing between the involved detector segments in case of 24 Compton-scattering or pair production are parameters bearing information on the beam track that could be extracted in a 25 comprehensive analysis. This would maximize the number of valid events on the expense of ‘information sharpness’, but 26 could eventually increase the total yield of information exploitable for range verification. Some aspects of such a strategy 27 have already been realized with the Prompt Gamma-Ray Timing (PGT) and the Prompt Gamma Peak Integration (PGPI) 28 techniques proposed recently. Data analysis schemes for a more generalized approach have not yet been developed, but the 29 hardware to be used can already be sketched: Prompt gamma rays should be detected with scintillation detector modules 30 consisting of single pixels with individual light readouts and independent electronic channels, similar to those developed for 31 PET-MR. Prompt gamma-ray detection in this context is, however, much more demanding with respect to dynamic range, 32 ——— * Corresponding author. Tel.: +49-351-458-7414; fax: +49-351-458-7263; e-mail: guntram.pausch@oncoray.de *Manuscript Click here to view linked References