ESTRO 2024 - Abstract Book

S4205

Physics - Intra-fraction motion management and real-time adaptive radiotherapy

ESTRO 2024

from Target Systemelektronik with a throughput of 1×10 6 s -1 enabled high-resolution time and energy spectrometry. Proton range deviations were induced by placing PMMA plates just in front of the phantom, simulating patient swelling or mispositioning. Two situations were considered: a global range shift (GRS) and a local range shift (LRS) when either the entire irradiation field or part of it was covered with the plates.

Results:

The investigated PGT system was found to have a constrain of 450×10 3 s -1 on the processed count rate which constitutes less than 50% of its maximum throughput. This is the consequence of the pulse pile-up rejection algorithm implemented to enhance the accuracy of time determination. With a typical treatment spot duration of 2.5 ms, the maximum number of detected events per treatment spot was ~10 3 . After subtracting time-uncorrelated background and applying an energy filter to select mainly PG-induced events, fewer than 400 events remained per one clinical spot in the detector. Although the detectors were placed inside collimators, PGs from the RC still contributed to measured time distributions by forming an additional peak formerly the region of interest (ROI) (PGs from the target). Even though this impact can be allocated, PGs from the RC increase the total load on detectors and reduce the ROI contribution. The effect becomes more pronounced for protons with lower energies which deposit more energy in the RC rather than in the target, and for that cases, more than 70% of all events belong to PGs from the RC.