Monte Carlo Simulation Framework for the Evaluation of PET Detector Designs in Charged Particle Therapy Applications

Charged particle therapy uses ionizing radiation beams to deliver dose precisely, while sparing nearby healthy tissue. Positron emission tomography (PET) is an imaging technique used to perform in-vivo range verification in charged particle therapy by detecting where the therapeutic particles have actually interacted, through the detection of annihilation radiation following the decay of positron emitters induced in the patient by the incident beam. The use of dedicated PET detectors placed close to the patient is preferable to using whole body scanners as it maximizes the detection efficiency when radioinduced activity is at its maximum, reduces blurring from biological washout and allows imaging of short-lived 15 O, particularly important in oxygen-rich tissue organs the brain. In this work, we propose a framework to evaluate the performance of PET detector designs in charged particle therapy applications, by Monte Carlo simulations of real patient treatments with artificially-induced range shifts by modulating beam energy or scaling tissue densities. Compared to irradiating phantoms of different materials with pencil beams, the use of CT images and treatment plans from real patients allows one to simulate in a more realistic way the real clinical conditions in which the PET detectors will be used. We have evaluated the proposed method by simulating real patient treatments with arbitrary range shifts by modulating beam energy, detecting the positron annihilation radiation with a dedicated PET detector design of our group. Results show that range variations as small as 1 mm can be identified, validating the use of the proposed method in the design and validation of novel PET detector designs for range verification in particle therapy.