Use of a Si/CdTe Compton Camera for Real-Time Monitoring of Annihilation Gamma Rays Generated by Carbon Ion Beam Irradiation.

The application of annihilation gamma-ray monitoring to the adaptive therapy of carbon ion radiotherapy (C-ion RT) requires identification of the peak intensity position and confirmation of activated elements with annihilation gamma-rays generated at the C-ion-irradiated site from those transported to unirradiated sites. Real-time monitoring of C-ion-induced annihilation gamma-rays was implemented using a Compton camera in a mouse model. An adult C57BL/6 mouse was anesthetized, and C-ion beams were directed into the abdomen at 1 × 10 particles/s for 20 s. The 511 keV annihilation gamma-rays, generated by the interaction between the irradiated C-ion beam and the target mouse, were detected using a silicon/cadmium telluride (Si/CdTe) Compton camera for 20 min immediately after irradiation. The irradiated site and the peak intensity position of 511 keV gamma emissions due to C-ion beam irradiation on a mouse were observed at the abdomen of the mouse by developing Compton images. Moreover, the positron emitter transport was observed by evaluating the range of gamma-ray emission after the C-ion beam irradiation on the mouse. Our data suggest that by confirming the peak intensity and beam range of C-ion RT with Si/CdTe-based Compton camera, it would be possible to reduce the intra-fractional and inter-fractional dose distribution degradation. Therefore, the results of this study would contribute to the future development of adaptive therapy with C-ion RT for humans.