@misc{oai:repo.qst.go.jp:00069895,
 author = {Yonai, Shunsuke and Matsufuji, Naruhiro and Kanai, Tatsuaki and et.al and 米内 俊祐 and 松藤 成弘 and 金井 達明},
 month = {Oct},
 note = {In proton and carbon-ion radiotherapies, undesired radiation exposure in normal tissues around a treatment volume is less than that in the conventional radiotherapies because of the physical property known as the Bragg peak. In addition, carbon-ion beams can reduce the undesired exposure laterally because of less scattering power. Such exposure is always considered in a treatment planning. However, undesired exposure far from the treatment volume cannot be considered in the treatment planning, because it is caused by secondary radiation as well as leakage primary particles. Though this exposure is considerably lower than that near the treatment volume, it is not negligible to estimate the risk of secondary cancer especially for the young patients. In particular, the assessment of the secondary neutrons that inevitably produced within the patient and beam line devices is very important due to the potency of their biological effect. As the first step in assessing the risk, we have measured spatial and energy distributions of the neutrons and neutron ambient dose equivalents using Bonner sphere system (BSS) [1] and a rem meter, WENDI-II [2] at Heavy Ion Medical Accelerator in Chiba (HIMAC) treatment room.  On the other hand, the distributions of the absorbed dose and the biological effectiveness in phantom are required to assess the risk, and Monte Carlo calculation plays a key role due to a difficulty of the measurement. In this study, measured in-air neutrons at the patient position (in the direction orthogonal to the beam axis) in passive carbon-ion radiotherapy were compared with those calculated with the Monte Carlo code, PHITS to verify the accuracy. Our calculations underestimated epithermal neutrons resulting from scattering by the beam line devices due to the lack of the calculational geometry modeling, but could reproduce the measured ambient dose equivalents well because they were dominated by neutrons energies above 0.1 MeV., NEUDOS-11},
 title = {COMPARISON OF MEASESURED AND CALCULATED IN-AIR SECONDARY NEUTRONS IN PASSIVE CARBON-ION RADIOTHERAPY},
 year = {2009}
}