前列腺癌放疗的摆位误差分析

Analysis of set-up errors during radiotherapy of prostate cancer

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.