机载千伏级CBCT监测鼻咽癌IMRT摆位误差的分析

目的探讨应用机载千伏级CBCT监测鼻咽癌患者调强放疗疗程中摆位误差的变化和影响因素。方法选取经病理检查确诊的鼻咽癌早期患者15例,行调强放疗。患者每周按原始计划标志点摆位,利用机载KV-CBCT扫描获取摆位误差,每周计算所有患者在三维方向和水平面旋转摆位误差平均值、标准差及95%可信区间（CI）;分析摆位误差随疗程进行的变化情况;探讨体重指数（BMI）和体重变化对摆位误差的影响。结果患者在腹背、头脚、左右3个坐标轴和水平面旋转的摆位误差均值分别为-0.1833 cm、-0.0322 cm、0.0967 cm和-0.8333°。随疗程进行摆位中心点向腹侧移位,BMI≥25患者在左右方向及水平面旋转的系统误差较BMI〈25患者明显;患者体重下降会引起摆位中心点往腹侧偏移和水平面逆时针旋转。结论 BMI≥25鼻咽癌IMRT患者有必要进行自适应放疗;放疗疗程中体重减少超过7.10%时,需要调整放疗计划。

Analysis of Setup Errors of IMRT for Nasopharyngeal Carcinoma with On-board KV-CBCT

Objective To investigate the application of KV-cone beam CT（CBCT） to monitor variance and influence factors of the setup errors of fractionated intensity-modulated radiation therapy（IMRT） for nasopharyngeal carcinoma.Methods 15 patients diagnosed with early nasopharyngeal carcinoma by pathology were selected and were treated by fractionated IMRT.Patients were posed by the original positions every week in order to get fractional setup errors with on-board KV-CBCT.The mean values,standard deviations,95% confidence intervals（CI） of three dimensional and the horizontal rotation errors were calculated.Analyze the effects of body mass index and weight loss on setup errors.Results The mean values of set up errors on ventral-dorsal,cranial-caudal,medio-lateral directions and rotation were-0.1833 cm,-0.0322 cm,0.0967 cm,-0.8333°.The displacements increased with the treatment progress along the ventral-dorsal direction,absolute values of the first setup errors,the system errors of the medio-lateral direction and the rotation errors in the patients with BMI≥25 were more obvious than those with BMI25.Weight loss can result in the center of actual setup position shifting to the ventral direction and horizontal rotation counterclockwise.Conclusion The nasopharyngeal carcinoma patients with BMI≥25 should be treated by adaptive radiation therapy.The treatment planning should be adjusted when the weight lost is over 7.10% during the treatment course.