現今放射治療大都採用強度調控放射治療方法(Intensive Modulation Radiation Therapy)，此方法把治療計劃系統所設計的治療方式及輻射劑量藉此方法讓病人接受計劃性的劑量。但隨著強度調控愈趨複雜，驗證直線加速器給予病人劑量和治療計劃是否一致性逐漸被重視且必要；在這過程中必需先把臨床劑量資料輸到治療計劃系統內做完整且妥善的校正(commission)，此篇研究主要的目的就是如何微調治療計劃系統內的round leaf end position 參數(offset)使得做模型化後計算結果更接近實際量測結果。用Elekta直線加速器及Pinnacle ADAC 7.6 version治療計劃系統做此實驗，先開一個10cm×10cm的照野，之後再開一個10cm×5cm的右半照野及10cm×5cm的左半照野，及5cm×5cm的1/4象限照野（左半照野、上右半照野、下左半照野、下右半照野）去驗證治療計劃系統所校正的正確性，之後再去驗證整體劑量的表現。結果發現當在半照野的準直儀邊緣切過中心射束軸時，實測的劑量比治療計劃系統所算出還來得高時，必需調整round leaf end position的offset參數變小，使得準直儀的物理劑量曲線往外退才會有較低的輸出，以至於在計算治療病人的MU才會變小；反之，如果實測的劑量比治療計劃系統所算出還來得低時，必需調整round leaf end position的offset參數變大，使得準直儀的物理劑量曲線往內退才會有較高的輸出，以至於在計算治療病人的MU才會變大；善用此微調參數可以讓治療計劃系統所算出的劑量和實測的劑量差異值變化小於1%內，這是這實驗最重要的結論。

Intensity Modulation Radiation Therapy treatment planning usually implement a lots of segmentations to form the desired dose distribution. If the isocenter is splitted by MLC，the dose verification result would be affected significantly by the round leaf end position. This study shows the dose delivery affected by round leaf end position in IMRT. ADAC version 8.0d is used for IMRT planning, Farmer 0.6cc ion chamber embedded in solid water phantom and PTW electrometer were used for dose verification check. The ion chamber usually set up at the isocenter for dose verification check. Round leaf position adjusted to "positive" or "negative" lead to the dose measurement coincident compared to that of desired dose in the case of MLC split on isocenter in IMRT. The chamber longitudinal axis parallel or perpendicular to MLC wall shape was also studied to see the orientation effect of chamber measurement. If planning default round leaf position tab was utilized to set the leaves offset tables，也e dose measurement errors might come up to 6% especially when MLC split the isocenter point. If the measurement dose is positive to planning desired dose, the leaves end position should adjusted forward toward to the isocenter to compensate the lack of attenuation. On the contrary, the leaves should be adjusted backward toward to isocenter for the negative dose measurement. The adjustment of round leaves end positions provide a good solves in IMRT dose verification errors problems.