利用不同測量系統實施弧形刀之劑量驗證

Dosimetric Verification of Volumetric Modulated Arc Therapy by Different Measurement Systems

許義昌(Yi-Chun Hsu)；許義勇(Yi-Yong Hsu)；熊敬業(Ching-Yeh Hsiung)；曾千惠(Chian-Hui Tseng)；陳信雄(Hsin-Hsiung Chen)

弧形刀 ； 劑量驗證 ； 點劑量 ； Volumetric Modulated Arc Therapy ； Dose Verification ； Point dose

台灣應用輻射與同位素雜誌

11卷2期（2015 / 06 / 01）

1107 - 1114

繁體中文

本研究目的是評估弧形刀（Volumetric Modulated Arc Therapy; VMAT）之放射治療劑量之準確性，選擇17個VMAT治療病患進行劑量測量，其中包含頭頸癌6位，胸部癌5位，骨盆腔癌6位。使用Elekta Synergy直線加速器及Pinnacle 9.2之SmartArc運算。點劑量之驗證是使用PTW pinpoint游離腔進行絕對劑量測量，點劑量評估是否符合±3%規範。2D-array及EBT3膠片與分別搭配VeriSoft與FilmQA驗證軟體來分析劑量分佈，並分別歸一化在最大劑量點，評估方法為Gamma-index method，3mm／3%、3 mm／2%、2 mm／2%來評估。點劑量差異值介於-1.0%至-6.9%，而整體平均值±標準差為-3.5%±1.6%，治療方式簡單，會有較多點劑量符合±3%規範。以頭頸癌、胸部癌、骨盆腔癌來分析點劑量之差異，其平均值±標準差分別為-4.5%±1.5%、-3.1%±1.9%、-3.0%±1.4%，頭頸癌誤差最大、其次為胸部癌、骨盆腔癌誤差則最小。2D-array與EBT3膠片於Gamma-index method 3mm/3%、3mm/2%、2mm/2%，其平均值±標準差分別為98.4±2.4、94.0±6.2、90.5±8.8，90.9±5.9、85.5±6.9、76.6±8.8，2D-arraygamma passing rate明顯高於EBT3膠片，無論使用何種評估標準。於劑量梯度變化較大處進行點劑量之測量，可了解腫瘤體積與正常組織交界處或劑量不均勻處，劑量變化狀況。使用2D-array與EBT3膠片二維劑量驗證系統，2D-array提供了VMAT高精準度之測量結果，而EBT3底片於本研究中發生測量系統誤差，但這需要再確認。本研究使用pinpoint游離腔與2D-array可明確得知VMAT於放射治療劑量之分佈準確性。

The purpose of this study was to investigate the accuracy of Volumetric Modulated Arc Therapy. Seventeen VMAT cases were selected in this study to proceed the dose verification. A commercial Elekta Synergy linear accelerator and SmartArc algorithm in Pinnacle 9.2 was used. The PTW pinpoint chamber was used for absolute point dose measurement. The point dose was assessed ± 3% criteria. The 2D-array and EBT3 film were normalized to the maximum dose and analyzed the dose distribution respectively with VeriSoft and FilmQA softwares. We performed gamma comparison with 3mm / 3%、3 mm / 2%、2 mm / 2% criteria to evaluate the results for the 2D-array and EBT3 film. The point dose error were from -1.0% to -6.9%, while the overall mean ± standard deviation was -3.5% ± 1.6%. We had better results within the point dose specification ± 3% in simple treatment techniques. For head and neck, thoracic, and pelvic cases, we found the differences of point dose, in mean ± standard deviation were -4.5% ± 1.5%、- 3.1% ± 1.9%、- 3.0% ± 1.4% respectively. The maximum discrepancy was found in head and neck cancer, then the thoracic cancer, and pelvic cancer error was minimum. The dose distribution evaluation with 2D-array and EBT3 film by Gamma-index method, 3mm / 3%、3mm / 2%、2mm / 2% , the average value ± standard deviation, were 98.4 ± 2.4, 94.0 ± 6.2, 90.5 ± 8.8, 90.9 ± 5.9, 85.5 ± 6.9 and 76.6 ± 8.8, respectively. The 2D-array gamma passing rate was significantly higher than EBT3 film in all evaluate criteria. In high dose gradient region, point dose measurements can realize the dose variation from the tumor and normal tissue at the junction or dose inhomogeneity. Using the 2D-array and EBT3 dose verification system, the 2D-array showed great accuracy in VMAT measurement results. The EBT3 film measurement occurred in system uncertainty in this study, but this requires further confirmation. In this study, pinpoint chamber and the 2D-array can confirm that the accuracy of the radiation dose distribution in the VMAT.