マルチリーフコリメータの位置精度が強度変調放射線治療の線量分布に及ぼす影響

摘要

強度変調放射線治療（intensity modulated radiation rntherapy；IMRT）は，治療計画装置（radiation therapy rnplanning system；RTP）により最適化されたビーム群をrn複数の方向から照射し，標的に高線量を照射するとrn同時にその周囲の正常組織への線量軽減を図ることrnができる音台療法である．%In multileaf collimator (MLC)-based intensity modulated radiation therapy (IMRT), the dose is influenced by the uncertainty of MLC driving control. In this study, we examined the influence of MLC driving control accuracy on dose evaluation (gamma analysis) by evaluating 60-day MLC driving control accuracy (stationary positioning accuracy and positioning reproducibility) once a week as well as measuring IMRT dose distribution. The MLC positioning accuracy accompanied variation over time and tended to expand by 0.1 to 0.15 mm in one week and about 1 mm in 60 days. In terms of reproducibility, errors were within 0.2 mm for more than 95%. For prostate IMRT, when MLC stationary positioning accuracy was around 1 mm, no significant difference was observed in the pass rate in gamma analysis. Therefore, the results suggest that regular maintenance by setting a permissible value determined by the MLC positioning accuracy test can be an effective indicator in the future for maintaining the safety of IMRT.