基于4D-CT呼吸门控技术的肝转移癌放射治疗剂量学研究

Dosimetric Study of Radiotherapy for Liver Metastasis Cancer Based on 4D-CT Respiratory Gating Technology

目的基于4D-CT确定肝转移癌的运动特征,比较3D-CT、4D-CT和门控CT计划的几何学和剂量学的差异。方法选取从2018年9月至2019年12月期间在本单位治疗的9位肝转移患者,每位患者分别进行3D-CT扫描和加上时间维度的4D-CT扫描,并选择呼吸末40%~60%的时相重建的平均图像作为门控CT;在每套CT图像上勾画肿瘤可见病灶大体肿瘤靶区(Gross Tumor Volume,GTV),分别加上不同的外扩边界得到计划靶区体积(Planning Target Volume,PTV)3D、PTV4D和PTVGate,为每套CT的靶区设计治疗计划,同一位患者的三种不同靶区计划的处方和布野方式相同,比较三套计划中靶区和危及器官的体积大小和剂量学差异。结果研究表明,9位患者的原发病灶GTV在头脚方向运动明显大于左右和前后方向,平均数值分别为(0.75±0.37)、(0.16±0.08)、(0.45±0.244)cm。同时靶区PTV3D的体积最大,平均值(117.11±65.06)cm^3,PTV4D靶区体积的平均值为(84.92±52.14)cm^3,PTVGate靶区体积最小,其平均值为(65.81±42.74)cm^3。三种计划靶区PTVs的剂量D1、D99和Dmean差异不大,没有统计差异。对正常器官的保护,肝脏的平均剂量Plan3D为(11.35±5.49)Gy,Plan4D为(10.22±5.73)Gy,PlanGate的剂量最小为(9.144±5.462)Gy。在右肾的保护上,平均剂量从Plan3D的6.36 Gy降到了门控计划的3.93 Gy(P=0.049)。胃的高剂量从19.47 Gy降到15.42 Gy(P=0.048),所以门控计划对肝脏、右肾和胃的保护明显优于其他两个计划,但是在小肠及脊髓的剂量比较没有统计学差异。结论我们的研究证实了门控技术在肝转移癌患者放射治疗中能够减少PTV的体积,从而更好的保护正常器官。

Objective To determine the motion characteristics of liver metastatic cancer based on 4D-CT and compare the geometric and dosimetric differences between 3D-CT,4D-CT and gated CT plans.Methods Nine patients with liver metastases treated in our unit from September 2018 to December 2019 were selected.Each patient underwent a 3D-CT scan and a 4D-CT scan with a time dimension respectively,and the average images of time phase reconstruction at the end of respiration from 40%to 60%were selected as gated CT;The tumor lesion GTV was delineated on each set of CT images,and PTV3D,PTV4D and PTVGate were obtained by adding different outer boundary and the treatment plan was designed for the target area of each CT.The prescription and distribution of three different target area plans in the same patient were the same,and the volume and dosimetry of target area and OARS were compared among the three sets of plans.Results The study showed that the primary lesions of 9 patients with GTV movements in the head and foot directions were significantly larger than the left and right and front and back directions,the average values were(0.75±0.37)cm,(0.16±0.08)cm and(0.45±0.244)cm.At the same time,the volume of the PTV3D tumor target area was the largest,with an average value of(117.11±65.06)cm^3,the average value of the PTV4D target volume was(84.92±52.14)cm^3,and the volume of the PTVGate target area was the smallest,with an average value of(65.81±42.74)cm3.The doses D1,D99 and Dmean of the three planned target area PTVs were not significantly different,and there was no clinical statistical difference.For the protection of normal organs,the average liver dose of Plan3D was(11.35±5.49)Gy,Plan4D was(10.22±5.73)Gy,and the minimum dose of PlanGate was(9.144±5.462)Gy.In the protection of the right kidney,the average dose decreased from 6.36 Gy of Plan3D to 3.93 Gy of the gated plan(P=0.049).The high dose of the stomach decreased from 19.47 Gy to 15.42 Gy(P=0.048),so the gating plan’s protection of the liver,right kidney and stomach was significantly better than the other two plans,but there was no statistical difference in the dose of the small intestine and spinal cord.Conclusion Our research confirms that gating technology can reduce the volume of PTV during radiotherapy for patients with liver metastases,thereby better protecting normal organs.