Clinical application of autoactivation PET imaging derived from C-12 ion radiotherapy

In the heavy ion therapy, the nuclear interaction yields lighter nuclear fragments, the positron emitters, when the projectiles penetrate through targets. This is called as 'autoactivation'. These induced positron emitters distribute in the vicinity of the range of the primary particles. C-11 particles are formed as a by-product of the treatment using C-12 ion beam. This distribution of C-11 can be measured with positron emission tomography (PET). Various kinds of positron emitters are formed when the target is irradiated by C-12 ion beam, but the amount of other particles than C-11 or O-15 is small and they decay away in short time. O-15 also decays away very quickly. We mainly measure the annihilation gamma rays of positron emitter C-11 by PET after the heavy ion therapy. If the spatial distributions of these positron emitters derived from fragmentation reactions in heavy ion therapy can be detected by PET and PET images of appreciable quality can be taken, we can verify the positioning of the primary ion beams in patient treatment. Based on some preliminary experiments, such as polymethyl methacrylate block phantom irradiation studies and rabbits irradiation studies, we proceeded to patient imaging studies. Clinical application of PET imaging of autoactivation derived from C-12 ion radiotherapy was studied. Quality of the image of autoactivation in each region from the brain to lower pelvis was checked. We also designed and introduced the patient whole body fixation system for autoactivation PET measuring. It is very important to perform the PET measurement under exactly same positioning of patient as Heavy Ion Medical Accelerator in Chiba (HIMAC) therapy. By using this fixation system, it should be possible to compare radioisotope (RI) distribution with therapy planning. (author)