3D打印乳腺癌补偿膜厚度对容积旋转调强治疗计划的剂量学影响研究

Study on the influence of 3D-printed compensation film of breast cancer on VMAT dosimetry

目的:研究讨论不同厚度的3D打印补偿膜在乳腺癌根治术后患者的靶区剂量均匀性、浅表皮肤剂量、机器跳数(MU)、适形指数(CI)、均匀指数(HI)和危及器官(OAR)的剂量学区别。方法:运用Monaco计划设计系统,对在医院行乳癌根治术后的10例乳腺癌患者分别设计补偿膜厚度为0 mm组、5 mm组、10 mm组和15 mm组的4组计划;将补偿膜电子密度设定为1.24,用PMT3D打印机打出补偿膜,采用Elekta直线加速器行放射治疗。处方剂量为50 Gy/25次,2 Gy/次,在相同的优化函数标准下开展逆向计算,比较4组计划的剂量HI值、靶区CI值、机器跳数(MU)、靶区、心脏和患侧肺的受量。结果:补偿膜为0 mm、5mm、10 mm和15 mm的4组计划中机器跳数(MU)随补偿膜厚度的增加而先减少后增加,在补偿膜厚度为5 mm组的机器跳数(MU)最少;而CI随着补偿膜厚度的增加不断减少,4组计划的机器跳数(MU)、CI比较,差异有统计学意义(F=15.236,F=8.125;P<0.05)。10例患者4组计划中心脏的V20、V30和Dmean的剂量差异比较,均有统计学意义(F=13.254,F=8.112,F=9.023;P<0.05)。剂量都是先增加后减少,5 mm组计划所受剂量最高,V_(20)在0 mm组计划所受剂量最小,V_(30)在10 mm组计划所受剂量最小,Dmean在0 mm组计划所受剂量最小。结论:乳腺癌根治术后容积旋转调强治疗中,组织补偿膜的厚度对乳腺癌靶区的机器跳数(MU)影响较大,在补偿膜厚度为5 mm的时候,机器跳数(MU)最少。随着组织补偿膜厚度的不断增加导致心脏的受量增加,但补偿膜厚度对患侧肺的剂量影响不明显。

Objective: To study and discuss the dosimetric differences of different thicknesses of three dimensional(3D) compensation film on the homogeneity of target volume, the dosage of superficial skin, machine unit(MU),conformity index(CI), homogeneity index(HI) and organ at risk(OAR) of patients after they underwent radical mastectomy. Methods: The Monaco plan design system was used to respectively design 4 sets of plans for the thickness of compensation film of 10 patients with breast cancer after they underwent radical mastectomy in hospital, which included 0 mm group, 5mm group, 10 mm group and 15 mm group. The electronic density of the compensation film was set to 1.24, and the compensation film was printed by PMT 3D printer. The Elekta linear accelerator was adopted to conduct radiotherapy. The prescription dose was 50 Gy/25 times and 2 Gy/time. The inverse calculation was implemented under the same optimization function standard. And then, the HI value of dose, CI value of target region,the machine unit(MU), target region, heart and the affected side of lung among 4 groups were compared. Results: In the 4 groups of plan, the MU increased after decreased with the increasing of the thicknesses of compensation film,and the MU was least in 5 mm group of compensation film. The CI continuously decreased with the increasing of the thickness of compensation film. The differences of MU and CI among 4 groups of plans were significant(F=15.236,F=8.125, P<0.05). The differences of V20, V30 and Dmean of heart among 4 groups of plan in 10 patients were significant(F=13.254, F=8.112, F=9.023, P<0.05). The doses of them appeared decrease after increase, and the dose of 5 mm group of plan was highest, and the received dose of V20 was least in 0 mm group of plan, and that of V30 was least in 10 mm group of plan, and that of Dmean was least in 0 mm group of plan. Conclusion: In the VMAT after radical mastectomy, the influence of the thickness of compensation film of tissue is larger on MU of target region of breast cancer, and it is least when the thickness is 5 mm. The received dose of heart increases with the increasing of the thickness of compensation film of tissue, however the influence of the thickness of compensation film on the dose of the affected side of lung is not obvious.