@article{oai:repo.qst.go.jp:00045952,
 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},
 issue = {10},
 journal = {Radiation Measurements},
 month = {May},
 note = {Undesired radiation exposure in normal tissues around a treatment volume in proton and carbon-ion radiotherapies is less than that in the conventional radiotherapies due to physical and/or biological properties of charged particles. Such exposure is always considered in a treatment planning, however, undesired  exposure  in  normal  tissues  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 may be 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. The distributions of the absorbed dose and the biological effectiveness in phantom/patient are required to assess the risk, and Monte Carlo calculation plays a key role due to a dif fi culty of the measurements. In this study, comparison of measured and calculated in-air neutrons at the patient position in the Heavy Ion Medical Accelerator in Chiba (HIMAC) treatment room are performed to verify the accuracy of the Monte Carlo code, PHITS. Our calculations underestimated  epithermal  neutrons  measured  by  Bonner  sphere  system.  This  discrepancy  may  be caused by an insuf fi ciency of the calculational geometry modeling, consequently an underestimation of neutrons scattered and moderated by the beam line devices. However, it is unlikely that the underestimation signi fi cantly contribute to the dose estimation in phantom. On the other hand, the calculation reproduced the measured ambient dose equivalents well because they were dominated by neutrons above 0.1 MeV. This result showed that the PHITS code has a potential ability to evaluate the neutron exposure of the patient in passive carbon-ion radiotherapy.},
 pages = {1369--1373},
 title = {Comparison of measured and calculated in-air secondary neutrons in passive carbon-ion radiotherapy},
 volume = {45},
 year = {2010}
}