Development of a graphite calorimeter for absolute dosimetry

In radiotherapy, high precision estimation of absorbed dose to water is required. The graphite calorimeter is one of most suitable detectors for absolute dosimetry due to direct measurement of energy deposit in principle. Many Western countries tend to adopt the calorimetry to determine the standard absorbed dose and become to be capable of deciding the absorbed dose to water in precision of about 0.6% for photon and electron beams. Despite the recent progress of particle therapy, parameters such as w-value and stopping power ratio for ionization chambers in the particles is not obtained accurately. Therefore, that causes uncertainty in determination of the absolute dose. We developed a graphite calorimeter to obtain high precision absorbed dose to water and reduce the uncertainty. (author)