乳腺癌根治术后放疗靶区外放边界的分析及验证

Analysis and verification of target margin for post-mastectomy radiotherapy for breast cancer

目的:回顾性分析乳腺癌根治术后放疗中的摆位误差,由此计算CTV外扩至PTV的外放边界,并通过模拟摆位误差验证此外放边界是否合适。方法:选取接受乳腺癌根治术后放疗的患者40例,其中左乳腺癌患者20例,右乳腺癌患者20例。根据治疗期间采集的CBCT图像确定摆位误差,计算出外扩边界。在TPS中模拟摆位误差,比较在此外扩边界下的剂量学差异。结果:全组患者左右、头脚、腹背方向的摆位误差分别为(2.09±2.48)、(2.57±2.52)和(2.88±2.54)mm;CTV外扩至PTV的边界分别为6.24、7.99、7.17 mm。在此外放边界下模拟摆位误差,CTV的各项剂量学指标无统计学差异,PTV的D_(95)、D_(98)、D_(max)、D_(min)有统计学差异,健侧乳腺D_(max)、Dmean和脊髓D_(max)有统计学差异,其他危及器官剂量学指标无统计学差异。在左右和腹背方向模拟摆位误差3 mm时,计划的γ通过率<95%。结论:摆位误差对PTV、脊髓、健侧乳腺的剂量影响较大。与头脚方向相比,剂量分布受左右和腹背方向摆位误差的影响更大。当摆位误差超过3 mm时需要对其进行修正。

Objective To calculate the CTV-PTV margins based on the retrospective analysis on the setup errors of post-mastectomy radiotherapy for breast cancer,and to simulate the setup errors for verifying whether the margin is appropriate.Methods Forty breast cancer patients,including 20 patients with left-sided breast cancer and 20 patients with right-sided breast cancer,who received post-mastectomy radiotherapy were enrolled.According to the CBCT images collected during the treatment,the setup errors were deter_(min)ed,and the margins were calculated.The setup errors were simulated in TPS for comparing the dosimetric differences under the target margins.Results The setup errors in left-right,superior-inferior and anterior-posterior directions were(2.09±2.48),(2.57±2.52)and(2.88±2.54)mm,respectively,and the CTV-PTV margins were 6.24,7.99 and 7.17 mm,respectively.There were statistically significant differences in D_(95),D_(98),D_(max) and D_(min) of PTV,D_(max) and Dmeanof the unaffected breast and D_(max)of spinal cord,but not in the dosimetric parameters of CTV;and no statistically significant difference was found in the dosimetric parameters of other organs-at-risk.When the setup errors in left-right and anterior-posterior directions were 3 mm,Gamma passing rate was less than 95%.Conclusion Setup errors have great dosimetric effects on PTV,spinal cord and unaffected breast.The dose distribution is more affected by the setup errors from left-right and anterior-posterior directions compared with superior-inferior direction.When the setup error is larger than 3 mm,it should be corrected.