目的：本篇為回溯性研究，比較發泡劑模具（α-cradle）和全身固定器搭配真空包（vacuum bag）對於肝癌病患的放射治療的固定效果。同時計算出計畫靶體積（planning target volume, PTV）所需的安全範圍（safe margin）。 材料與方法：自 2014 年 1 月 1 日始至 2015 年 12 月 31 日止，收集本科符合收案條件的所有 肝癌病人，在治療前執行錐狀射束電腦斷層攝影（cone beam computed tomography, CBCT） 後的位移結果。根據 CBCT 三維各軸（X、Y、Z）位移數值計算分析，得到平均誤差（overall mean，M）、系統誤差的標準差（system error ，Σ）、隨機誤差的標準差（random error ，σ）等 數值。並利用 2.5Σ+0.7σ，計算出計畫靶體積所需的安全範圍。 結果：發泡劑組與固定器搭配真空包組在 X、Y、Z 軸的位移平均值與標準差為 0.4±1.8 和 0.3±1.8，p = 0.83；0.6±2.6 和 0.2±2.5，p = 0.52；-0.6±2.0 和 0±1.5，p = 0.15，單位為 毫米（mm）。在使用發泡劑固定器的病人，建議計畫靶體積在 X 軸需增加 5.7 mm，Y 軸 8.7 mm，Z 軸 6.8 mm 的安全範圍；在使用全身固定器搭配真空包的病人，建議計畫靶體積在 X 軸需 增加 6.1 mm，Y 軸 9.3 mm，Z 軸 5.4 mm 的安全範圍。 結論：本研究結果顯示兩種固定器的固定效率並無顯著差異。對於肝癌病人，建議計畫靶體積在 X 軸需增加 7 mm，Y 軸 10 mm，Z 軸 7 mm 的安全範圍。

Purpose : The aim of this study was to compare the positioning reproducibility of α-cradle and vacuum bag for patients with hepatocellular carcinoma via cone beam computed tomography (CBCT). Safe margins for planning target volume (PTV) were also measured. Methods and Materials : From January 1, 2014 to December 31, 2015, CBCT data of 68 patients with hepatocellular carcinoma were collected. For patient positioning, α-cradle was used until October 2014. Vacuum bag with abdominal compression was used since October 2014. Patients were imaged before treatment to ascertain inter-fraction motion. Overall mean (M), standard deviation of system error (Σ) and standard deviation of random error (σ) were used to compare the positioning reproducibility. Safe margins for PTV were derived from the equation: 2.5Σ+0.7σ. Results : There were 35 patients in α-cradle group and 33 patients in vacuum bag group. The overall means and standard deviations of the X, Y, and Z axes in α-cradle group and in vacuum bag group were 0.4 ± 1.8 mm and 0.3 ± 1.8 mm (p = 0.82), 0.6 ± 2.6 mm and 0.2 ±2.5 mm (p = 0.52), -0.6 ± 2.0 mm and 0 ± 1.5 mm (p = 0.15), respectively. The PTV safe margins in the X, Y, and Z axes of α-cradle group were 5.7 mm, 8.7 mm and 6.8 mm, respectively. The PTV safe margins in the X, Y, and Z axes of vacuum bag group were 6.1 mm, 9.3 mm and 5.4 mm, respectively. Conclusions : There was no significant difference of positioning reproducibility between α-cradle and vacuum bag. For patients with hepatocellular carcinoma, the PTV safe margins in the X, Y, and Z axes were 7 mm, 10 mm and 7 mm, respectively.