目的：了解多葉準直儀（MLC）系統性誤差對於體積調控弧形治療（VMAT）在劑量分佈和生物劑 量參數的影響。 材料與方法：以 AAPM TG-119 報告為依據，本研究製作了五個 VMAT 治療計畫（多顆腫瘤、攝 護腺腫瘤、頭部腫瘤、寬鬆C 形腫瘤以及嚴格C 形腫瘤）。各治療計畫中加入兩個方向（+ open, - close）四種程度的系統性誤差值（±0.5 mm, ±1 mm, ±2 mm, ±3 mm）。分別以各計畫在分 析閾值為 3%/3 mm 與 2%/2 mm 的加馬指標分析（gamma index analysis）結果及靶體積和危急 器官的等效均勻劑量（equivalent uniform dose）計算結果來評估 MLC 系統性誤差對於劑量分佈 和生物劑量參數的影響程度。 結果：每單位 MLC 系統性誤差（mm）在 open 方向對於加馬指標分析閾值在 3 mm/3% 和 2 mm/2% 的結果影響分別為 -11.69% 及 -18.44%，而在 close 方向則分別為 -9.73% 和 -15.30%。 若要達成 90% 以上的加馬指標通過率，在閾值為 3 mm/3% 和 2 mm/2% 時可允許的誤差容許 值在 open 方向分別為 0.86 mm 及 0.54 mm，而在 close 方向則分別為 1.03 mm 和 0.65mm。 每單位 MLC 系統性誤差（mm）對於靶體積及危急器官 EUD 的差異百分比分別為 6.30% 和 5.20%。 結論：本研究建議的 MLC 系統性誤差容許值為 1 mm，和 TG142 的建議相同。放射治療中心需 具有完善的 MLC 品質保證計畫，以確保病患獲得正確的處方劑量及避免嚴重的併發症產生。

Purpose : The purpose of this study was to understand the consequence of MLC systematic errors on the VMAT technique in the dose distribution. Material and Methods : Five VMAT treatment plans (multiTumor, Prostate, Head, C_loose_plan, and C_strict_plan) followed TG-119 instructions were created. MLC systematic errors were simulated for error magnitudes of ±0.5 mm, ±1 mm, ±2 mm, and ±3 mm in X1 bank (+ open, - close). The 3 mm/3% and 2 mm/2% gamma index analysis and PTVs and OARs equivalent uniform dose (EUD) were used to evaluate the impact of MLC systematic errors on the dose distribution and the biological dose parameter. Materials and Methods : In total 97 patients with breast cancer were included, they were treated with hybrid intensity-modulated radiotherapy (Hybrid IMRT) for 50.4 Gy in 28 fractions. Patients were evaluated at three months after treatment through the observation of the change of chest computed tomography image. The final endpoint of complication was according to Arriagada’s classification. Patients with grade 1+ change on CT images were defined as a complication of radiation pneumonitis. We evaluated the correlation of radiation pneumonitis and mean ipsilateral lung dose. We established LKB NTCP model through calculated the equivalent uniform dose (EUD) of ipsilateral lung and validated the model performance. The NTCP model was mainly used to investigate the dose-response curve for complications of radiation pneumonitis and provided dose parameters to prevent complication of endemic breast cancer patients. Result: The average 3 mm/3% and 2 mm/2% gamma index passing rate was decreased by 11.69% per mm and 18.44% per mm in the open direction and 9.73% per mm and 15.30% per mm in the close direction. The tolerance of MLC systematic errors to achieve > 90% criteria for 3%/3 mm and 2 mm/2% gamma analysis was 0.86 mm and 0.54 mm in the open direction and 1.03 mm and 0.65 mm in the close direction. The impact of average EUD difference on PTVs and OARs was 6.30% per mm and 5.20% per mm. Conclusion : The present study suggested that the tolerance of systemic MLC errors was 1mm. Radiation treatment centers should have adequate MLC quality assurance program to ensure clinical outcomes and avoid serious complications.