2013 Fiscal Year Final Research Report

Reduction of neutron exposure for carbon-ion radiotherapy

Research Project

Project/Area Number	23602008
Research Category	Grant-in-Aid for Scientific Research (C)
Allocation Type	Multi-year Fund
Section	一般
Research Field	Medical Physics/Radiological Technology
Research Institution	Nagoya University
Principal Investigator	KOMORI Masataka 名古屋大学, 医学(系)研究科(研究院), 准教授 (30392228)
Project Period (FY)	2011 – 2013
Keywords	炭素線治療 / 拡大照射法 / 中性子被ばく / モンテカルロシミュレーション
Research Abstract	In passive particle radiotherapy, secondary neutrons are produced by nuclear reaction because most incident particles collide with collimators. We additionally set a fixed-aperture collimator (FC) to the upper stream in a beam delivery system to reduce neutron exposure. This study was performed by Monte Carlo toolkit Geant4. The beam delivery system of Heavy Ion Medical Accelerator in Chiba (HIMAC) was constructed in Geant4. We calculated the neutron ambient dose equivalent at patient position with and without FC. Incident particle was carbon-ion of 290 and 400 MeV/n. The diameter of laterally uniform irradiation field was 100 and 200 mm. The measured secondary neutron ambient dose equivalent without FC was reproduced in Geant4. The neutron dose equivalent was approximately reduced to 40% for 400 MeV/n carbon-ion beam, by inserting the FC optimized not to affect the lateral dose distribution. We can found out that the neutron exposure can be reduced by inserting the FC.