体重指数对图像引导乳腺癌调强放射治疗摆位误差的影响

Effect of body mass index on setup errors of image-guided intensity modulated radiation therapy for breast cancer

目的探讨体重指数(BMI)对保乳术后乳腺癌患者在图像引导治疗下摆位误差及外扩边界的影响。方法回顾性选取2020年1月至2021年7月广州市第一人民医院接受放射治疗的80例保乳乳腺癌患者作为研究对象,根据BMI将患者分成过轻组(BMI<18.4 kg/m^(2))、正常组(18.4 kg/m^(2)≤BMI<24 kg/m^(2))、超重组(24 kg/m^(2)≤BMI<27 kg/m^(2))和肥胖组(BMI≥27 kg/m^(2)),每组20例。放疗时应用锥形束CT(CBCT)进行扫描,采集患者放疗中左右位(LAT)、头脚位(LNG)和腹背位(VRT)三个方向(又分别称X轴、Y轴和Z轴)的摆位误差,计算各组因BMI不同摆位误差的差别,并根据公式MPTV=2.5Σ+0.7σ计算最佳的靶区外扩边界。结果考虑BMI情况下,四组患者X轴和Z轴摆位误差整体比较,差异无统计学意义(P>0.05);四组患者Y轴摆位误差整体比较,差异有统计学意义(P<0.05)。过轻组和正常组X轴上外扩边界相近,超重组和肥胖组X轴上外扩边界相近,但过轻组和正常组小于超重组和肥胖组X轴上的外扩边界;Y轴上的外扩边界随BMI的增大而增大;Z轴上的外扩边界在不同BMI中相近。结论乳腺癌调强放射治疗Y轴摆位误差与BMI存在相关性,随BMI的增大,摆位误差也逐渐增大。不同BMI患者的摆位误差可进一步指导医师确定靶区面积扩边范围,采用不同标准适当扩大或缩小外扩边界,从而提高治疗精度。

Objective To investigate the influence of body mass index(BMI)on the setup errors and external expansion boundary of breast cancer patients after breast conserving surgery under image-guided therapy.Methods A total of 80 breast conserving breast cancer patients received radiation therapy in Guangzhou First People's Hospital from January 2020 to July 2021 were retrospectively selected as the study subjects.According to BMI,the patients were divided into underweight group(BMI<18.4 kg/m^(2)),normal group(18.4 kg/m^(2)≤BMI<24 kg/m^(2)),overweight group(24 kg/m^(2)≤BMI<27 kg/m^(2))and obesity group(BMI≥27 kg/m^(2)),with 20 cases in each group.During radiotherapy,20 patients were scanned using cone-beam computed tomography(CBCT)to collect setup errors in the latitude(LAT),longitude(LNG),and verticality(VRT)directions(also known as the X axis,Y axis,and Z axis)during radiotherapy.The differences in setup errors due to different BMI were calculated for each group,and calculate the optimal target area external expansion boundary according to the formula MPTV=2.5Σ+0.7σ.Results Considering BMI,the overall comparison of X-axis and Z-axis setup errors among the four groups of patients was not statistically significant(P>0.05).The overall comparison of Y-axis setup errors among the four groups of patients showed statistically significant difference(P<0.05).The X-axis external expansion boundary was similar between the underweight group and normal group,while the X-axis external expansion boundary was similar between the overweight group and obesity group.However,the X-axis external expansion boundary of underweight group and normal group were smaller than those of the overweight group and obesity group.The external expansion boundary on the Y-axis increased with the increase of BMI.The external expansion boundary on the Z-axis was similar in different BMI. Conclusion There is a correlation between the Y-axis setup error of intensity modulated radiation therapy for breast cancer and BMI. With the increase of BMI, the positioning error increases gradually. The setup errors of different BMI patients can further guide physicians to determine the target area expansion range, and use different standards to appropriately expand or reduce the external expansion boundary, thereby improving treatment accuracy.