Measurement of Spatial Distributions of Radiation Quality for Carbon Therapy Beams

放医研では、臨床線量を、電離箱で測定した物理線量と比例係数管で測定したLETスペクトルから求められるRBEのかけ算で算出している。しかしながらこの手法は繁雑であり、比例係数管は空間分解能が悪いために、治療の臨床線量分布のような複雑な場を測定できない。そこでシンチレータを使用して、個の問題を解決し、LETスペクトルから直接臨床線量を求める手法を確立した。World Congress on Medical Physics and Biological Engineering 200

Microdosimetric Measurements and Estimation of Human Cell Survival for Heavy-Ion Beams

The microdosimetric spectra for high-energy beams of photons and proton, helium, carbon, neon, silicon and iron ions (LET = 0.5-880 keV/um) were measured with a spherical-walled tissue-equivalent proportional counter at various depths in a plastic phantom. Survival curves for human tumor cells were also obtained under the same conditions. Then the survival curves were compared with those estimated by a microdosimetric model based on the spectra and the biological parameters for each cell line. The estimated alpha terms of the liner-quadratic model with a fixed beta value reproduced the experimental results for cell irradiation for ion beams with LETs of less than 450 keV/um, except in the region near the distal peak