患者生理特征参数对乳腺癌调强放疗摆位误差影响的研究

Investigation of patient characteristics associated with setup errors in intensity-modulated radiotherapy after breast-conserving surgery

背景与目的:逆向调强放疗技术已广泛应用于全乳放疗,为有效地代偿摆位误差的不确定性,目前还是将临床靶区向计划靶区外放合适的边界,但对于不同乳腺癌患者外放相同的边界是否妥当尚存在争议,利用锥形束计算机断层扫描(cone-beam computed tomography,CBCT)对接受调强放疗的乳腺癌患者进行三维方向摆位误差分析,探讨各生理特征参数与摆位误差的相关性并进行初步分组,为个性化靶区外放边界提供参考依据。方法:回顾性分析2019年1—12月在复旦大学附属肿瘤医院接受调强放疗的乳腺癌保乳术后患者的临床资料,共纳入97例,利用CBCT分析患者的生理特征参数(包括年龄、肿瘤位置、体重指数、胸围及患侧乳腺体积)对摆位误差的影响。对于连续变量,按中位数分组;对于肿瘤位置,将患者按左右进行分组,并个性化确定靶区外放边界。结果:患者体重指数、胸围和乳腺体积分别与头脚方向(Pearson=0.40,P<0.01)、头脚方向(Pearson=0.43,P<0.01)和左右方向(Pearson=0.42,P<0.01)呈中度正相关,同时三者分组在头脚方向的摆位误差比较差异有统计学意义(t=-3.923,P=0.001;t=-5.182,P=0.001;t=-2.712,P=0.008)。并且胸围及乳腺体积分组在左右方向的摆位误差比较差异也有统计学意义(t=-2.124,P=0.036;t=-3.550,P=0.001)。按体重指数、胸围和乳腺体积中位数分组确定计划靶区外放边界在左右、头脚和前后方向上分别为3.1~4.5、4.6~8.0和4.9~5.3 mm。结论:乳腺癌保乳术后调强放疗患者的体重指数、胸围及乳腺体积与摆位误差存在相关性,推荐根据以上生理特征参数为不同乳腺癌患者确定合理的个性化靶区外放边界。

Background and purpose:Intensity-modulated radiation therapy(IMRT)is a widely used radiotherapy technique in whole breast irradiation.Therefore,planning target volume(PTV),with appropriate margins from clinical target volume(CTV),would adequately account for the setup uncertainty.However,it is still controversial regarding whether the protocol-required margin around the CTV adequately accounts for setup inaccuracies.The aim of this study was to determine the impacts of patient characteristics on the magnitude of geometric setup errors in patients with breast cancer and to obtain individualized PTV margins.Methods:A total of 97 patients treated with IMRT after breast-conserving surgery in Fudan University Shanghai Cancer Center from January 2019 to December 2019 were reviewed.Cone-beam computed tomography(CBCT)scan records were used to analyze setup errors.The impacts of patient characteristics on setup errors were also analyzed,including age,tumor location,body mass index(BMI),chest circumference and breast volume.Population in the two groups was compared in terms of distribution of the median patient characteristics,and individualized PTV margins were obtained.Results:The BMI,chest circumference and breast volume showed moderate positive correlation with superior-inferior(Pearson=0.40,P<0.01),superior-inferior(Pearson=0.43,P<0.01),and rightleft directions(Pearson=0.42,P<0.01),respectively.Meanwhile,there were significant differences in setup errors of superior-inferior direction(t=-3.923,P=0.001;t=-5.182,P=0.001;t=-2.712,P=0.008)among the three groups,and significant differences were also observed in setup errors of left-right direction between the chest circumference and breast volume groups(t=-2.124,P=0.036;t=-3.550,P=0.001).When dividing patients into two groups on the basis of median value of BMI,chest circumference,breast volume and the margin in left-right,superior-inferior and anterior-posterior directions were 3.1-4.5,4.6-8.0 and 4.9-5.3 mm,respectively.Conclusion:Patient characteristics such as BMI,chest circumference and breast volume were significantly correlated with geometric setup errors.The individualized PTV margins were recommended to adequately compensate for the setup variation detected according to patient characteristics.