乳腺癌保乳术后调强放疗摆位误差相关因素分析

Factors associated with set-up errors in intensity-modulated radiotherapy after breast conserving surgery

目的分析热塑体膜和乳腺托架两种固定方式用于乳腺癌保乳术后调强放射治疗的摆位误差,以及相关临床因素对其的影响。方法回顾性分析2016年1月至2018年6月接受调强放射治疗的乳腺癌保乳术后患者的临床资料,共纳入34例,18例采用热塑体膜固定,16例采用乳腺托架固定。利用锥形束CT比较两组摆位误差的分布,计算群体系统误差和随机误差,并分析临床因素对摆位误差的影响。结果两组患者的摆位误差总体以热塑体膜组为优,但仅在Ty和Ry两个维度上差异有统计学意义(t= 2.385、2.427,P< 0.05)。依据系统和随机误差计算PTV外放边界,热塑体膜组在Tx、Ty、Tz方向分别为2.65、4.36、2.87 mm,乳腺托架组分别为5.71、6.07、4.20 mm。多因素分析发现,BMI是影响Ry摆位误差的潜在因素(t=-2.785,P< 0.05)。结论乳腺癌保乳术后接受放疗的患者,采用热塑体膜固定可以有效减少摆位误差,缩小PTV外扩边界,这一点在高BMI的患者中表现的更为明显。

Objective To evaluate the difference of set-up errors between thermoplastic mask and breast bracket in patients receiving intensity-modulated radiotherapy after breast conserving surgery, and the impact of clinical factors associated with set-up errors. Methods A total of 34 patients treated with intensity-modulated radiotherapy after breast conserving surgery from January 2016 to June 2018 were reviewed. Eighteen patients were fixed with thermoplastic mask, and sixteen were with breast bracket. Weekly CBCT scan records were used to analyze set-up errors, and group systematic and random errors were computed. The influence of clinical factors on set-up errors was also analyzed. Results The immobilization technique with thermoplastic mask showed great superior in comparison with breast bracket;however, only in the Ty (translation) and Ry (rotation), the differences had significance. Based on group systematic and random errors, PTV margins in Tx, Ty and Tzwere 2.65, 4.36 and 2.87 mm in thermoplastic mask group, as well as 5.71, 6.07 and 4.20 mm in breast bracket group, respectively. Multi-factor regression analysis showed that BMI was independent factors affecting set-up errors. Conclusions Compared with breast bracket, the immobilization technique with thermoplastic mask has the potential of reducing set-up errors and PTV margins in patients receiving intensity-modulated radiotherapy after breast conserving surgery, especially in patients with high BMI.