Dose verification in situ is highly required in proton therapy. We have developed an electron-tracking Compton camera (ETCC) which consists of gaseous time projection chamber (TPC) and a position-sensitive scintillator. Since the TPC performs the electron-tracking, the ETCC is able to reconstruct Compton scattering event-by-event, and to reject the back ground strongly. In this presentation, we demonstrate the feasibility of dose verification using the ETCC, and the gamma-ray images are compared between the annihilation gammas and prompt gamma rays of higher energy.
Using the ETCC, we obtained the gamma-ray image for the Polymethyl methacrylate (PMMA) phantom irradiated with 290-MeV/u carbon beam at Heavy Ion Medical Accelerator in Chiba (HIMAC), Japan, with a particle (carbon) rate of up to 5 x 106 cps. We succeeded in obtaining gamma-ray imaging (0.4 – 2.0 MeV) in beam, and gamma-ray imaging peak was consistent with simulation data using the PHITS code.
In this experiment, we used Gd2SiO5(Ce) scintillator as the absorber. Here, angular resolution of the Compton camera is related to be energy resolution of the scintillator. Recently, we have developed novel scintillation material, (Gd, La)2Si2O7(Ce) with better energy resolution than Gd2SiO5(Ce). To improve the angular resolution of the ETCC, we also show the scintillation properties of the novel scintillator in this paper.