[Development of a multi-layer ion chamber for measurement of depth dose distributions of heavy-ion therapeutic beam for individual patients].

In heavy-ion radiotherapy, an accelerated beam is modified to realize a desired dose distribution in patients. The setup of the beam-modifying devices in the irradiation system is changed according to the patient, and it is important to check the depth dose distributions in the patient. In order to measure dose distributions realized by an irradiation system for heavy-ion radiotherapy, a multi-layer ionization chamber(MLIC) was developed. The MLIC consists of 64 ionization chambers, which are stacked mutually. The interval between each ionization chamber is about 4.1 mm water. There are signal and high voltage plates in the MILC, which are used as electrodes of the ionization chambers and phantom. Depth dose distribution from 5.09 mm to 261.92 mm water can be measured in about 30 seconds using this MLIC. Thus, it is possible to check beam quality in a short amount of time.