3DCT联合4DCBCT在中下叶肺癌SABR放疗靶区外放边界中的应用研究

Application of 3DCT and 4DCBCT in evaluating target margin in SABR for lung cancer in middle or lower lobe

目的:利用四维锥形束CT(4DCBCT)扫描获取放疗靶区摆位误差和呼吸运动误差,计算肿瘤立体定向消融放射治疗(SABR)中计划靶区体积(PTV)外放边界大小。方法:回顾性分析19例中下叶肺癌SABR治疗患者,治疗前4DCBCT扫描,共72次扫描图像。根据4DCBCT与定位CT的配准结果,评估放疗靶区分次间摆位和呼吸运动误差,确定PTV外放边界大小。结果:放疗靶区摆位误差在左右、上下、前后3个方向上分别为(0.11±0.29)、(0.02±0.58)、(0.05±0.26)cm,放疗靶区呼吸运动误差在3个方向上分别为(-0.06±0.34)、(0.09±0.68)、(0.06±0.23)cm,利用ICRU83#报告公式计算PTV外放边界,在3个方向上分别为1.13、2.15、0.90 cm。结论:4DCBCT可有效评估放疗靶区摆位和呼吸运动误差,并确定中下叶肺癌SABR治疗中PTV外放边界大小。利用本方法计算的外放边界比原来RTOG提出的外放标准更加精确,可个体化评估放疗靶区外放边界。

Objective To obtain setup errors and errors caused by respiratory motion using four-dimensional cone-beam computed tomography(4DCBCT),thereby calculating planning target volume(PTV)margin in stereotactic ablative radiotherapy(SABR)for lung cancer in middle or lower lobe.Methods Nineteen patients who underwent SABR for lung cancer in middle or lower lobe were randomly selected for retrospective analysis.4DCBCT scan was conducted before treatment,and a total of 72 images were obtained.According to the image registration between 4DCBCT and CT for positioning,the inter-fractional setup errors of target areas and errors caused by respiratory motion were evaluated,thereby determining the size of PTV margins.Results The setup errors were(0.11±0.29),(0.02±0.58)and(0.05±0.26)cm in rightleft(RL),superior-inferior(SI)and anterior-posterior(AP)directions,respectively,and the errors caused by respiratory motion were(-0.06±0.34),(0.09±0.68)and(0.06±0.23)cm,respectively.The PTV margin calculated by the formula in ICRU83#report were 1.13,2.15 and 0.90 cm in RL,SI and AP directions.Conclusion 4DCBCT can be used to effectively evaluate setup errors and errors caused by respiratory motion and to determine PTV margin in SABR for lung cancer in middle or lower lobe.Compared with the margin standard provided by Radiation Therapy Oncology Group,the PTV margin calculated by the proposed method is more accurate.The proposed method can be used to individually evaluate PTV margin.