准直器角度对宫颈癌VMAT的剂量学影响

The dosimetry effect of VMAT with different collimator angles for cervical cancer

目的:比较两种不同准直器角度对晚期宫颈癌VMAT计划的剂量学影响,为晚期宫颈癌VMAT计划的设计提供临床参考。方法:选择11例晚期宫颈癌患者,每例病人分别设计两种不同准直器角的双弧VMAT计划,计划A和计划B的准直器角度分别为15°/345°和0°/90°。PTV处方剂量为45Gy/(25f·1.8Gy)。所有计划都满足95%的靶区体积达到处方剂量要求。比较每个计划PTV的适形性指数(CI)与均匀性指数(HI)以及膀胱、直肠、股骨头和双肾的体积剂量(V30、V40、V50和V18)和平均剂量(D mean)等参数。结果:两组计划靶区覆盖均能满足临床要求,但B计划的CI明显优于A组计划(0.75±0.03 vs 0.66±0.06;P<0.05),并且有相似的均匀性指数。与A计划相比,B计划在危及器官的体积剂量和平均剂量均明显低于前者(P<0.05)或者两者没有差别(P>0.05)。计划A、B两组膀胱和直肠的平均剂量(D mean)和体积剂量V40分别为:(4 500.70±218.28)c Gy vs(4 168.56±212.62)c Gy(P=0.000)和(83.43%±11.73%)vs(61.46%±9.47%)(P=0.000);(4 836.12±313.33)cGy vs(4 719.27±182.24)c Gy(P=0.121)和(97.05%±3.29%)vs(93.78%±6.60%)(P=0.066)。结论:对于晚期宫颈癌VMAT计划的设计,准直器角度为0°/90°的计划结果优于15°/345°的计划。不仅PTV的剂量分布有更好的适形性,而且能更好地保护危及器官。因此推荐使用0°/90°的准直器角度设计晚期宫颈癌的VMAT计划。

Objective： To compare the effect of VMAT plans with two collimator angles for advanced cervical cancer,and provide reasonable clinic guidance for designing the VMAT plan of advanced cervical cancer. Methods： Eleven cervical cancer patients treated by VMAT were selected,and two double- arc VMAT plans were designed. The collimator angles of plan A and plan B were 15° /345° and 0° /90°,respectively. The prescribed dose of PTV was 45 Gy /（ 25f·1. 8Gy）. After ensuring the 95% target was irradiated to the prescription dose in the two plans,the dose volume histogram（ DVH） and the dose parameters,such as the volume dose（ Vx）,the average dose（ Dmean）,and the max dose（ Dmax） of OARs were evaluated. Results： Two plans were satisfied with the clinical requirements,but the CI of PTV of plan B were better than plan A significantly（ 0. 75 ± 0. 03 vs 0. 66 ± 0. 06,P〈0. 05）. Compared to plan A,the volume dose（ Vx） and the average dose（ Dmean） of all organ at risk（ OAR） were lower significantly（ P〈0. 05） in the plan B,or have no difference between two plans（ P〈0. 05）. the Dmeanand V40 of bladder and rectum for plan A and plan B were（ 4 500. 70 ± 218. 28） c Gy vs（ 4 168. 56 ± 212. 62） c Gy（ P = 0. 000） and（ 83. 43% ± 11. 73%） vs（ 61. 46% ± 9. 47%）（ P = 0. 000）,and（ 4 836. 12 ± 313. 33） c Gy vs（ 4 719. 27 ± 182. 24） c Gy（ P = 0. 121） and（ 97. 05% ± 3. 29%） vs（ 93. 78% ± 6. 60%）（ P = 0. 066）,respectively. Conclusion： The results of double- arc VMAT plans of 0° /90° collimator angle were better than that of 15° /345° collimator angle for advanced cervical cancer,which was due to have a better CI of PTV and could protect the OARs preferably. Therefore,it is recommended to use 0 ° /90 ° collimator angle for double- arc VMAT plan designing of advanced cervical cancer.