目的：銳速刀（RapidArc）放射治療是利用旋轉臂（gantry）在旋轉的同時，藉由改變多葉式準直儀（multi-leaves collimator；MLC）的位置、照野內的輻射劑量率以及 gantry 旋轉速度，以達到體積調控弧形放射治療的目的。其中，為了減少 tongue and groove effect 以及提高劑量的空間解析度，準直儀（collimator）角度成為優化治療計劃的條件中不可或缺的主要參數之一。本研究目的即為找出適合攝護腺癌患者使用之治療計劃的準直儀旋轉角度。
材料與方法：於本科患者資料庫中挑選 15 位攝護腺癌患者，分別選擇 15 度、30 度、45度、
60 度、75 度等 5 種不同的準直儀角度重新進行銳速刀治療計劃。所有患者在進行銳速刀治療計劃的優化過程中，對腫瘤治療體積（planning target volume；PTV）和各危急器官（organ atrisk；OAR）使用相同的劑量限制（dose constraint）及器官權重（priority）以減少影響結果的變異性。原廠建議 45 度為最佳的準直儀角度，因此以 45 度作為標準，比較改變準直儀角度各計劃在腫瘤最大劑量值（dose maximum；Dmax）、均勻性（homogeneity index；HI）及順形度（conformal index；CI）以及危急器官（organ at risk；OAR）所接受的劑量。結果：以 45 度當作標準來進行比較，治療計劃在準直儀旋轉 15 度、30 度、60 度和 75度所計算的最大劑量值分別有 20%（3/15）、73.3%（11/15）、53.3%（8/15）和 20%（3/15）的比例小於45 度的最大劑量值。在 15 度、30 度、60 度和 75 度分別有 6.7%（1/15）、46.7%（7/15）、40%（6/15）和 13.3%（2/15）的比例有較好的均勻性。而在 15 度、30 度、60 度和 75 度分別有 40%（6/15）、60%（9/15）、40%（6/15）和 13.3%（2/15）的比例有更好的順形度，對於危急器官所接受的劑量都可以控制在劑量限制的範圍內。結論：在執行銳速刀放射治療技術時，本研究結果顯示準直儀設定 30 度角對攝護腺癌的患者而言，和其他四種不同的角度可以容易得到較好的結果。

Purpose : RapidArc is the latest VMAT technique that treat patient very quickly by optimizing the MLC shape, radiation dose rate, and gantry rotation speed in a single arc radiotherapy. In addition to reduce tongue and groove effect and to raise the spatial resolution of high dose area, collimator angle has become a determining factor for RapidArc optimization. This study try to find the most suitable collimator angle for RapidArc treatment planning system for patients with prostate cancer.
Materials and Methods : Fifteen prostate cancer patients were selected to re-optimize the treatment plan of RapidArc. Five different collimator angles (15°, 30°, 45°, 60°, 75°) were used while we doing the plans.
RapidArc treatment plan optimization, using the same optimization parameters, such as dose constraint and priority for planned target volume and critical organ. The plan of 45 degree of collimator angle was used as the basis of comparison of the maximum dose(Dmax), homogeneity
index(HI)and conformal index(CI)in the tumor and the dose received by critical organs.Result : To use the plan of 45 degree of collimator angle as the standard. When collimator rotated 15,30,60 and75 degrees, there were 20% (3/15), 73.3% (11/15), 53.3% (8/15) and 20% (3/15) ratio of
the Dmax lower than the Dmax calculated by 45 degree respectively. When collimator rotated 15, 30,60 and 75 degrees, there were 6.7% (1/15), 46.7% (7/15), 40% (6/15) and 13.3% (2/15) ratio of results got more homogeneous distribution than 45 degree. And when collimator rotated 15, 30, 60 and 75 degrees, there were 40% (6/15), 60% (9/15), 40% (6/15) and 13.3% (2/15) ratio of the results has more conformal distribution. Further more, the dose which accepted by critical organs were all under the dose constraints.Conclusion : In order to reduce the tongue and groove effect and to improve spatial resolution of high dose area, collimator in the treatment process must be rotated. The results of this study show that the 30 degree of the collimator angle for prostate cancer patients has better result compared to another four different angles.