乳腺托架固定下全乳调强放疗CBCT测定摆位误差的研究

目的 探讨乳腺癌保乳术后乳腺托架固定下全乳调强放疗的摆位误差和影响因素,明确临床靶体积外扩至计划靶体积的边界。方法 选取肿瘤医院2016-2017年间乳腺癌保乳术后接受全乳大分割调强放疗的患者30例,其中左侧乳腺癌患者15例,右侧乳腺癌患者15例。所有患者均采用乳腺托架体位固定。比较放疗计划系统图像与放射治疗期间锥形束CT的位移,确定摆位误差,并计算临床靶体积外扩至计划靶体积的边界。不同情况的摆位误差比较采用t检验。结果 全组患者共拍摄锥形束CT图像151套,平均每人(5.0±1.3)套。全组患者摆位误差在x、y、z轴的位移分别为(2.2±1.7)、(3.1±2.5)、(3.3±2.3) mm,CTV至PTV外扩边界分别为6.39、10.00、8.57 mm。放疗第1周摆位误差与后续治疗摆位误差在z轴方向有统计学差异(3.7±2.5) mm和(2.6±1.6) mm,P=0.002],体重指数超重比正常患者在z轴方向摆位误差显著增大(3.9±2.6) mm和(2.9±2.0) mm,P=0.033]。结论 乳腺癌保乳术后乳腺托架固定行全乳调强放疗时,推荐CTV至PTV的外扩边界为6~10 mm。建议增加放疗第1周的影像验证频率。

Study of setup error in cone beam CT for whole breast intensity-modulated radiotherapy with breast board immobilization

Objective To investigate the setup errors and influencing factors of the whole breast intensity-modulated radiotherapy (IMRT) after breast-conserving surgery, and to identify the margins from clinical target volume (CTV) to planning target volume (PTV). Methods Thirty patients with left-sided (n=15) or right-sided breast cancer (n=15) receiving whole breast hypofractionated IMRT with breast board immobilization after breast-conserving surgery in Cancer Hospital from 2016 to 2017 were enrolled. The kilo-voltage cone-beam computed tomography (CBCT) was used to compare the errors of planning CT and treatment unit and determine the setup errors. The margins from CTV to PTV were calculated. The setup errors under different conditions were statistically compared by t-test. Results A total of 151 sets of CBCT images were taken in the whole cohort,(5.0±1.3) sets per patient on average. The setup errors in the x-axis (left-right direction), y-axis (cranial-caudal direction) and z-axis (anterior-posterior direction) were (2.2±1.7) mm,(3.1±2.5) mm and (3.3±2.3) mm, respectively. The margins from CTV to PTV were 6.39 mm, 10.00 mm and 8.57 mm, respectively. The setup error in anterior-posterior direction in the first week was (3.7±2.5) mm, significantly larger than (2.6±1.6) mm in the following week (P=0.002). The setup error of the patients with overweight or obesity was (3.9±2.6) mm, significantly higher than (2.9±2.0) mm in those with normal weight in the z-axis direction (P=0.033). Conclusion The margins from CTV to PTV are recommended to be ranged from 6 to 10 mm during hypofractionated whole breast IMRT with breast board immobilization after breast-conserving surgery. More frequent imaging verification should be applied in the first week of IMRT.