目的：探讨前列腺癌仰卧位放疗时左右、头脚、前后方向的摆位误差及各方向的旋转误差。方法收集2011年10月至2013年6月接受前列腺癌根治性放疗的患者25例，采用仰卧位体模固定，锥形束CT（ CBCT）骨配准校位，分析左右、头脚、前后方向的平均摆位误差及各方向的平均旋转误差。结果全放疗疗程中每例患者校位9次，共计225次。各方向的平均摆位误差：左右（0．19±0．18）cm，头脚（0．36±0．30）cm，前后（0．21±0．16）cm；其中左右方向摆位误差≥5mm占5．8％，头脚占24．3％，前后占8．0％。各方向旋转误差：轴位（1．07±1．03）°，头脚（0．82±0．66）°，水平（0．79±0．68）°。前5次与后4次摆位及旋转误差比较差异无统计学意义（ P＞0．05）。结论前列腺癌仰卧位放疗时，头脚摆位误差最大，左右及前后摆位误差相当，旋转误差较小可忽略不计。%Objective To analyze the set-up errors in the left-right( LR, X axis) , superoinferior ( SI, Y axis) and antero-posterior (AP, Z axis) directions and the rotations during radiotherapy of prostate cancer in the supine position. Methods Twenty-five prostate cancer patients who received radiotherapy from October 2011 to June 2013 were analyzed. All the patients were treated with intensity-modulated radiotherapy ( IMRT) in the supine position after external immobilization using thermoplastic shell. Measurements for set-up errors and rotations in X, Y, Z directions were collected from daily image-guided radiotherapy( IGRT, bony match) pre-treatment. The set-up errors and rotations were analyzed. Results Each patient received 9 fractions of measurement with a total of 225 fractions. Mean set-up errors were (0. 19±0. 18)cm, (0. 36±0. 30)cm, and(0. 21±0. 16)cm in the X, Y and Z axes, respectively. The set-up errors of≥5 mm was 5. 8%, 24. 3%, and 8. 0% of all measured fractions in the X, Y and Z axes, respectively. Mean rota-tions were (1. 07±1. 03)°, (0. 82±0. 66)°, and (0. 79±0. 68)°in the axis, vertical, and lateral directions, respectively. After com-paring the first 5 and the following 4 set-up and rotation errors, there were no significant differences( P>0. 05) . Conclusion The set-up errors is larger in the Y than in the X and Z axes during radiotherapy of prostate cancer in the supine position. The rotation errors are much smaller and can be omitted.
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