背景和目的：比較使用 Belly board（腹板）之俯臥位是否優於仰臥位式攝護腺癌放療，並計算直腸的直徑變化、直腸與攝護腺間距及評估治療劑量與體積直方圖（DVH）之關係。材料與方法：15 例攝護腺癌患者分別進行兩組骨盆電腦斷層掃描，分別是使用 Belly board 之俯臥位及沒有固定的仰臥位。每個病人在兩種擺位下的治療計劃皆使用 4-field box technique（方盒治療技術）三維適形放療（3DCRT）。使用 Wilcoxon signed-rank test 作統計分析，分析項目包括：直腸的幾何變化、直腸與攝護腺間距及重要器官的治療劑量與體積直方圖（DVH）分析。結果：患者於俯臥姿勢加腹板治療相對於患者在仰臥位置有較大的直腸前後徑和橫向徑為（p值= 0.003 和p = 0.031），和較大的攝護腺和直腸的中心間的距離（p 值= 0.002）。關於 DVHs數據，患者於俯臥治療導致治療部位的直腸體積較大（P = 0.015），意味著較低直腸劑量（p=0.002）和較小的直腸體積接受高輻射劑量（p = 0.001）。結論：攝護腺癌病人治療時使用Belly board（腹板）之俯臥位之固定方式對直腸直徑（前後向及橫斷面）都有顯著的增大（相較於仰臥位的固定方式），在直腸與攝護腺中心點間的距離也是使用Belly board（腹板）之俯臥位之固定方式有較大的距離，在劑量與體積的直方圖也顯示使用Belly board（腹板）之俯臥位之固定方式有較低的直腸輻射劑量可以降低放療引起的併發症。

Background and Purpose : To investigate the impact of supine position versus proneposition with belly-board on prostate radiotherapy by evaluation the geometric parameterchange between internal organs and treatment dose-volume histograms (DVHs).Materials and Methods : Fifteen patients with prostate cancer underwent pelvic CTscan in position of both prone with belly-board device and supine without immobilization.Four-field box three-dimensional conformal radiotherapy (3DCRT) treatmentplanning was planned for each patient in both positions. Geometric change includingdiameter of rectum, distant between critical organs and treatment DVHs were investigated.Wilcoxon signed-rank test was used for statistical analysis.Results : Patients in prone treatment position had both larger anterio-posterior diametersand transverse diameter of rectum (p = 0.003 and p = 0.031), and larger distancebetween the centers of prostate and rectum (p=0.002) than those of patients in supineposition. In regard to the DVHs data, prone treatment position resulted in larger rectalvolume (p = 0.015), lower mean rectal dose (p = 0.002) and smaller rectal volumereceiving high radiation dose (p = 0.001).Conclusions : Patients in prone treatment position with belly-board immobilizationhad both larger anterio-posterior diameters, transverse diameter of rectum, and largerdistance between the centers of prostate and rectum than those of patients in supineposition. Prone treatment position with belly-board device can reduce rectum dose,which may in turn decrease the risk of radiation-induced complications.