目的：估算正常組織併發症機率（ NTCP ）以評估放射治療計劃，特別是三度空間治療計劃。材料與方法：劑量體積直方圖可由電腦斷層攝影資料與放射劑量分佈計算而得。有效體積法是一種劑量體積直方圖之轉換技術。可將非均勻照射直方圖轉換成均勻照射直方圖，使此圖之體積為有效體積而劑量則等於最大劑量。非均勻照射之正常組織併發症機率（ NTCP ）可由已知之均勻照射全部及部分器官之併發症機率利用公式計算而得。結果：各器官之劑量體積直方圖由 Render-Plan 治療計劃系統計算而得。 各器官之有效體積用 Kutcher 有效體積法計算而得。 利用 Lyman 公式與常態分配表可估算得各器官之NTCP。結論：NTCP 的估算對放射治療計劃，特別是三度空間治療計劃的評估十分重要。 在評估治療計劃時，除了審視劑量分佈圖與劑量體積直方圖外，最好加上 NTCP 之估算，以使計劃評估更為有效與正確。istograms for various organs are obtained by calculationwith Render-Plan treatment planning system. Effective volumes for these organsare obtained by calculation with Kutcher's effective volume method. Calculationusing Lyman's model and table of the normal distribution, we obtained the NTCPvalues for these organs.Conclusion:During radiotherapy normal tissues are irradiated along with thetumor. Radiation oncologists try to minimize the dose to normal tissues whiledelivering a high dose to the tumor. Often this is difficult and complicationsarise due to irradiation of normal tissues. Estimation of NTCP is important forevaluation of 3-dimensional treatment plans. It is preferable to use NTCP as anadditional tool for plan evaluation, in conjunction with a review of graphicaldose distributions and dose volume histograms.