GATE Monte-Carlo Simulation of an MV-CBCT Flat Panel for Synergistic Imaging and Dosimetric Applications in Radiotherapy

The objective of this paper was to simulate mega-voltage cone beam computed tomography (MV-CBCT) for both imaging and dosimetric purposes, using a portal imaging device modeled on a dedicated Monte-Carlo platform. An X-ray flat panel detector mounted on a Siemens accelerator was modeled with Geant4 application for emission tomography (GATE) according to its geometrical and physical characteristics. This model was validated by simulating 2-D MV images of both a patient and an anthropomorphic phantom and then by reconstructing MV-CBCT volumes. Dose deposited during MV-CBCT procedure was simulated and compared to measurements obtained with dedicated detectors. Portal imaging was also used for simulating inverse reconstruction of dose distributions. The simulated MV-CBCT volumes showed a good agreement with the ground truth which was the computed tomography scans of the patient and the phantom. For dose reconstruction, comparison between GATE calculation and measurements from a matrix of ionization chambers gave between 92% and 96.1% of dose points passing the 3%/3 mm gamma test, depending on the field complexity. As a conclusion, the ability of GATE for concomitant imaging acquisition and dose estimation was demonstrated. This new virtual platform is able to reconstruct imaged volumes and to estimate doses deposited by simple and complex irradiation fields.