RADIOISOTOPES

Experimental researches on radiation protection in carbon ion radiotherapy were performed in the HIMAC treatment rooms. Some of the key results on dose assessments for medical exposure of patients, medical exposure of careers and comforters, and occupational exposure were introduced here. The undesired exposure to normal tissues outside the treatment volume was investigated by measurements with a portable neutron rem-meter and a tissue equivalent proportional counter. These results indicated that the secondary cancer risk after carbon ion radiotherapy are comparable or less than other external radiation therapy modalities. The doses to radiation technologists working in the carbon ion radiotherapy facility and careers and comforters of the patients from radioactive irradiation devices and patients induced by therapeutic carbon beam were estimated based on experimental measurements. These results demonstrated that the carbon ion radiotherapy facility can be safely operated by current Japanese regulations according to the ICRP recommendations. A lot of these results have been cited in the ICRP publication 127: Radiological protection in ion beam radiotherapy. We therefore believe that these researches offered a significant contribution toward the promotion of carbon ion radiotherapy.