@misc{oai:repo.qst.go.jp:00075621,
 author = {中路, 拓 and Nakaji, Taku},
 month = {Apr},
 note = {[Purpose] Carbon ion (C-ion) radiotherapy is better than the external photon radiotherapy because of C-ion’s higher concentration of dose and greater biological effects on the peripheral area of Bragg peak. The scanning method can realize the ideal shape of dose distribution for a coverage of target. It is important for passive method with a broad-beam to consider the radiation quality only along with depth for relative biological effectiveness (RBE). However, the lateral distribution of C-ion beam’s radiation quality must be considered for using scanning irradiation to confirm the uniformity of biological dose. In this study, the lateral radiation quality of C-ion beams is shown with the empirical model for biological dose estimation. 
[Method] The lateral dose, dose-averaged LET- (LETd) and RBE-distribution for of monochrome C-ion pencil beam with three incident kinetic energy (230, 290, 350 MeV/u) were derived with Monte Carlo tool Geant4.10.01.p03, respectively. The RBE as a biological index was calculated with a mixed-beam model, which is an empirical model developed by NIRS.
[Results] The more the kinetic energy increases, the more dose distribution of primary C-ion beam spread from 10 mm to 16 mm in Bragg peak area, which looks like three-Gaussian. While the shape of RBE-distribution is similar to dose one, LETd distribution looks like a shape of well, which has a peak region at around 5 to 10 mm of radius. 
[Discussion] The C-ion has known as a high-LET particle around Bragg peak, it’s especially about beam’s depth direction. Although the lateral distribution had been not known well, the LETd distribution became obvious as a well-shape distribution in this study. The lateral radiation quality is critical for a spot scanning method because the biological dose distribution must be conformed three-dimensionally about a number of spot, which is not like broad-beam method. 
[Conclusion] We showed the lateral distributions of C-ion beams. These results may help you get the knowledge to understand the biological effects of spot scanning method., 117th Scientific Meeting of JSMP},
 title = {The Monte Carlo simulation for lateral radiation quality of carbon ion beam with the empirical model},
 year = {2019}
}