Abstract ID: 153 Monte Carlo simulation study of orthogonal ray imaging for monitoring head radiotherapy

Abstract

OrthoCT (based on orthogonal ray imaging) is a novel imaging system under study at LIP that consists on the detection of radiation scattered in the patient and emitted perpendicularly to the incident beam [1] . This technique was designed to potentially assist external-beam radiotherapy (EBRT) treatments, being useful for on-board imaging and/or real-time EBRT monitoring. Such orthogonal rays can be collected by positioning a multi-sliced, collimator-based detector system parallel to the beam axis. OrthoCT provides computed tomography-like images without rotating the X-ray source about the target (patient) which highly decreases the irradiated region. Simulation studies have evaluated the feasibility of OrthoCT for monitoring possible variations that may occur in lung [2] and prostate irradiations [3] . In both studies, this technique has shown to be fully capable of detecting possible organ deviations and tumor size variations. In this work, the capability of OrthoCT to detect morphological variations during a pituitary-like irradiation was evaluated through GEANT4-based simulations. For that, an anthropomorphic phantom was used and two different scenarios were implemented: (1) phantom with empty nasal sinuses and (2) filled with biological tissue. Regarding the features of the simulated detection system, a realistic full OrthoCT detector was implemented including the multi-slice collimator, the scintillator crystals, and the charge electronic readout mode. The results show that the signal distribution provided by such radiation present a good visual agreement with the simulated dose and the phantom structures, with a clear detection of the changing morphological scenarios here studied.