Positron Emitter Depth Distribution in PMMA Irradiated With 130-MeV Protons Measured Using TOF-PET Detectors

Proton therapy for cancer treatment has a precise dose deposition capability owing to the nature of the interactions of heavy charge particles with matter resulting in a Bragg Peak. Uncertainties in the proton range can limit the scope of proton therapy. Academia Sinica PET employs a modular design for In-beam detection using SiPMs and crystals read out by STiC asic for range verification. In this work we report the depth distribution of the positron emitters from a PMMA sample irradiated with 130-MeV protons at the Chang Gung Memorial Hospital measured using a compact 32-channel setup. The timing capabilities of this system are assessed and presented. The depth dependence of the positron activity measured using coincidences agrees well with the Geant4 simulated distributions. Using a multiexponential fit function we estimate and compare the relative amounts of different positron emitting isotopes with the relative cross sections. The application of this method can be useful to estimate the anatomical changes between different treatment sessions. The modular design of the AS-PET currently under development at Academia Sinica is presented and the simulated images of the reconstructed positron activity for the palm sized modules are used to assess the range verification capability.