Estimations of relative biological effectiveness of secondary fragments in carbon ion irradiation of water using CR‐39 plastic detector and microdosimetric kinetic model

Abstract

Purpose To estimate relative biological effectiveness (RBE) ascribed to secondary fragments in a lateral distribution of carbon ion irradiation. The RBE was estimated with the microdosimetric kinetic (MK) model and measured linear energy transfer (LET) obtained with CR‐39 plastic detectors. Methods A water phantom was irradiated by a 12C pencil beam with energy of 380 MeV/u at the Gunma University Heavy Ion Medical Center (GHMC), and CR‐39 detectors were exposed to secondary fragments. Because CR‐39 was insensitive to low LET, we conducted Monte Carlo simulations with Geant4 to calculate low LET particles. The spectra of low LET particles were combined with experimental spectra to calculate RBE. To estimate accuracy of RBE, we calculated RBE by changing yield of low LET particles by ± 10% and ± 40%. Results At a small angle, maximum RBE by secondary fragments was 1.3 for 10% survival fractions. RBE values of fragments gradually decreased as the angle became larger. The shape of the LET spectra in the simulation reproduced the experimental spectra, but there was a discrepancy between the simulation and experiment for the relative yield of fragments. When the yield of low LET particles was changed by ± 40%, the change in RBE was smaller than 10%. Conclusions An RBE of 1.3 was expected for secondary fragments emitted at a small angle. Although, we observed a discrepancy in the relative yield of secondary fragments between simulation and experiment, precision of RBE was not so sensitive to the yield of low LET particles.

Secondary Radiation in Ion Therapy and Theranostics: A Review

“…Here, 11,12 C, 16 O, and 13,14,15 N had almost comparable LET [62]. Experimentally measured LET distribution of SCPs, for 380 MeV/u 12 C beam, was compared with the GEANT simulation [64,65]. The measured values were well reproduced by the simulation [65].…”

“…Another set of isotopes emerging as potential diagnostic and therapeutic nuclides are the two radioisotopes of Cu- 62,64 Cu [95,96,[98][99][100][101][102][103][104][105][106][107]. Cu is one of the most abundant trace transition elements in human body and plays a key role in various physiological processes.…”

“…Cu is one of the most abundant trace transition elements in human body and plays a key role in various physiological processes. Among the five radioisotopes of Cu, namely, 60,61,62,64,67 Cu, 62 Cu (half-life 9.67 min) decays by β+ emission and is used for diagnosis. 64 Cu with a half-life of 12.7 h decays by electron capture β+ and β-emission.…”

“…Among the five radioisotopes of Cu, namely, 60,61,62,64,67 Cu, 62 Cu (half-life 9.67 min) decays by β+ emission and is used for diagnosis. 64 Cu with a half-life of 12.7 h decays by electron capture β+ and β-emission. Electron capture results in the emission of Auger electrons which can be used for therapy [100].…”

“…Electron capture results in the emission of Auger electrons which can be used for therapy [100]. So 64 Cu is increasingly investigated for use in diagnosis as well as in therapy. In normal cells, Cu remains in the cytoplasm, but in tumor cells it migrates to the nucleus [98].…”