目的：比較傳統模擬定位技術(2-D)與現行電腦斷層影像三維治療技術(3-D)在放射線治療劑量上的差異，並確認傳統模擬定位技術在乳房相切照射技術的可行性。材料與方法：自1998年11月至1998年12月，十位在本科接受乳房相切照射治療的初期乳癌病患收入到此篇的研究體材內。病患使用發泡劑製做固定姿勢，進行傳統乳房相切照射的模擬攝影操作程序，取得傳統2-D治療技術的參數。之後，病患進行電腦斷層掃描，以擷取影像傳輸至3-D影像輔助治療計劃系統。比較3-D影像輔助治療計劃其最佳的劑量分佈與2-D治療參數（中心點、照野、旋轉臂角度及準直儀角度等）輸入至3-D影像輔助治療計劃系統之DVH，並計算所得的照射體積（如PTV、正常組織、肺部與心臟）。結果：此兩種技術計算其PTV的覆蓋比率為0.95±0.02。就正常組織，2-D在50%的劑量曲線內有較多的胸壁軟組織被含括，但兩者技術並沒有產生明顯差別（平均體積分別為2-D 703 ml±205 ml和3-D 539 ml±197 ml, t test p=0.146）。對同側的肺部而言，有相同的肺部照射體積百分比（2-D為75%±30%與3-D為76%±48%）。另外左側乳癌病患，心臟接受照射體積亦沒有不同（2-D為5.8 ml±4.2 ml, 3-D為5.4 ml±3.9 ml）。結論：我們的資料顯示，兩種技術無論在PTV、正常組織、肺部與心臟其分析資料無差別。在沒有CT模擬攝影機的時後，以傳統的2-D模擬攝影來執行乳房相切照射技術來執行，亦是一種可行的選擇。

Purpose: To compare the conventional 2-dimensional (2-D) simulation technique with CT- based 3-D planning method, and verify the feasibility of 2-D method for breast tangential irradiation. Materials and Methods: From November to December1998, ten successive patients with early-staged breast cancer were enrolled for this study. After immobilization with alpfa-cradle, patient underwent a conventional simulation-method to get the parameters for 2-D treatment plan. Patient also had a chest CT scan and these images were stored for subsequent 3-D treatment plan. These two treatment planning methods were retrospectively compared with their dose-volume histogram (DVH) of the irradiated targets (PTV normal tissue, lung and heart). Results: The PTV covering ratio (2-D vs. 3-D) of these two techniques is 0.95 ± 0.02. For the normal tissue, two-dimensional technique has more chest wall soft tissue included within 50% isodose curve, but there is no significant difference (mean volume 703 ml±205 ml for 2-D vs. 539 ml±197 ml for 3-D, t test p=0.146). For the ipsilateral lung tissue, both methods have equivalent irradiated percentage lung volume (7.5%±3.0% for 2-D vs. 7.6%±4.8% for 3-D). For left-sided breast cancer, the average irradiated heart volumes are 5.4 ml±4.2 ml (2-D) versus 5.8 ml±3.9 ml (3-D). Conclusions: Our analysis shows that both planning methods have equivalent irradiated dose-volume histograms. For circumstances where CT scan simulator is not available, conventional 2-D planning method is an acceptable alternative.