Absolute dosimetry using a graphite calorimeter in heavy-ion beams

In order to sophisticate the radiotherapy, high accuracy knowledge of the absorbed dose delivered to the patient is essential. Despite recent progress in carbon-ion therapy, accurate values for physical data such as the w value or mass stopping power ratios for ionization chamber dosimetry have not been obtained. The beam quality conversion factors obtained by the graphite calorimeter was compared with those recommended by the International Atomic Energy Agency technical report series no.398 (IAEA TRS 398) for the several ionization chambers in mono-energetic carbon-ion beams. The beam quality conversion factors indicated about 3% larger values than those from the IAEA protocol. The absorbed dose to water obtained by the calorimetry indicates about 3% larger value than that obtained by the ionization chamber dosimetry in spread-out Bragg peak (SOBP) carbon-ion beam. Using the beam quality conversion factors evaluated by the calorimetry, the absorbed dose in SOBP carbon-ion beams agreed with that obtained by the graphite calorimeter measurements at the SOBP center. (author)