摘要目的 通过锥形束CT (CBCT)分析肝癌患者术后简化调强放疗分次间和分次内的临床靶体积(CTV)误差.方法 12例肝癌患者放疗前、后均行CBCT.在瘤床放置金属标记,配准框包全所有金属标记,不包括肋骨、椎体等骨质,使用自动骨性配准.若放疗前平移误差＞3mm和(或)旋转误差＞3°则行在线校位后重复CBCT.12例患者共行214次CBCT成111组数据,111组可计算分次间左右(x)、头脚(y)、前后(z)方向CTV误差,70组可计算分次内CTV误差.计划靶体积(PTV)边界计算公式为2.0∑ +0.7σ(∑为系统误差,σ为随机误差).结果 x、y、z方向上分次间CTV平移误差分别为-0.03、-0.43、1.02 mm,∑分别为1.50、5.89、1.97 mm,σ分别为1.76、4.13、2.42 mm;分次内平移误差分别为0.04、0.86、-0.46 mm,∑分别为0.46、1.14、0.31 mm,σ分别为0.95、1.38、0.91 mm.PTV边界在x、y、z方向上分别为4.5、15.0、5.8mm.结论 肝癌患者简化调强放疗时CTV误差不可避免,使用术中放置瘤床金属标记行CBCT获得的数据真实准确.

abstractsObjective To evaluate the inter-and intra-fractional clinical target volume (CTV) positioning errors of patients receiving postoperative simplified intensity-modulated radiotherapy (SIMRT) using cone beam computed tomography (CBCT).Methods Twelve patients with liver tumors underwent postoperative SIMRT.CBCT images were acquired before and after the treatment.The clipbox volume for registration included the fiducial markers in the tumor bed and excluded the ribs and vertebral bodies.If any translational parameter of setup error before treatment exceeded 3 mm or rotational parameter exceeded 3°,the treatment couch was adjusted and a verification CBCT was acquired to assess residual setup error.Automatic bone match was used.A total of 214 acquisitions of CBCTs in 111 groups were analyzed.Inter-fractional translational CTV positioning errors in left-right (x),superior-inferior (y) and anterior-posterior (z) axis were calculated in 111 groups,and intra-fractional translational CTV positioning errors in 70 groups.Clinical to planning target volume (PTV) margins were calculated according to the formula:margin =2.0 ∑ + 0.7σ ( ∑ is systematic error,σ is random error).Results Inter-fractional translational CTV positioning errors in x,y and z axis were -0.03 mm,-0.43 mm,1.02 mm,with systematic error ( ∑ ) of 1.50 mm,5.89 mm,1.97 mm,and random error (σ) of 1.76 mm,4.13 mm,2.42 mm,respectively.Intra-fractional translational CTV positioning errors in the x,y,z axis were 0.04 mm,0.86 mm,- 0.46mm,with systematic error (∑) of 0.46 mm,1.14 mm,0.31 mm,and random error (σ) of 0.95 mm,1.38 mm,0.91 mm,respectively.The calculate CTV to PTV margins were 4.5 mm,15.0 mm,5.8 mm in the x,y,z axis,respectively.Conclusions The CTV errors were inevitable when patients with liver tumors received SIMRT.Fiducial markers placed in tumor bed during operation were helpful for accurate positioning error analysis.