Reconstruction of Irradiation Field from Prompt Gamma-rays in Geant4 Based Proton Therapy Simulation

A reconstruction of irradiation field from prompt gamma-rays and annihilation gamma-rays is an interest of particle therapy to verify the range of therapeutic beam and confirm the safety of patient. For the purpose of precision medicine in proton therapy, an irradiation field monitoring system is under development in the project "Tumor Response Observation System for Dose-volume delivers Guided Particle Therapy, TROS-DGPT". It is developing a hybrid beam online PET and electron tracking Compton Camera (II-BOLP/CCs). In TROS-DGPT project, a simulation tool has an important role to verify the mutual relationship among dose, radionuclide distributions inside a patient and reconstructed images from signals in imaging devices. In previous conference, we reported on the development of imaging device functions in Geant4 based particle therapy system simulation framework (PTSIM). In this paper, we report on results from the study about the irradiation field reconstruction in PTSIM by using prompt gamma-rays. The simulation was performed for proton beam with a target. The target's material was chosen from polyethylene, water, acrylic and soft tissue. A simple tubular detector was placed around the target to coincide the isocenter. Scorers were attached to the target and the detector, respectively. The irradiation field was reconstructed in the filtered back projection (FBP) method The reconstructed irradiation fields were compared with the absorbed energy distribution in the target. The range in reconstructed irradiation field shows some deviation in the peak depth from the absorbed energy distribution depending on material of the target.