PSI, Villigen PSI, Switzerland
University of Zurich, University Hospital, Zurich, Switzerland
Patient treatments in scanned proton therapy exhibit dead times, e.g. when adjusting beamline settings for a different energy or lateral position. On the one hand, such dead times prolong the overall treatment time, but on the other hand they grant possibilities to (retrospectively) validate that the correct amount of protons has been delivered to the correct position. Efforts in faster beam delivery aim to minimize such dead times, which calls for different means of monitoring irradiation parameters. To address this issue, we report on a real-time beam monitoring system that supervises the proton beam position and current during beam-on, hence while the patient is under irradiation. For this purpose, we sample 1-axis Hall probes placed in beam-scanning magnets and plane-parallel ionization chambers every 10 μs. FPGAs compare sampled signals against verification tables - time vs. position/current charts containing upper and lower tolerances for each signal - and issue interlocks whenever samples fall outside. Furthermore, we show that by implementing real-time beam monitoring in our facility, we are able to respect patient safety margins given by international norms and guidelines.
