宫颈癌术后阴道三维腔内近距离放射治疗两种施源器剂量学研究

目的: 比较宫颈癌根治术后行阴道三维腔内近距离治疗采用单通道柱状、双卵圆球两种施源器的剂量学差异，为宫颈癌术后行阴道三维腔内近距离放疗选择施源器提供参考。方法: 回顾性分析2018年6月12月于川北医学院附属医院肿瘤科完成阴道三维腔内近距离放射治疗的早期宫颈癌术后患者20例，每例患者均在接受宫颈癌根治手术后因有术后放疗指征，进行术后三维腔内近距离放射治疗。每例患者分别采用单通道柱状施源器、双卵圆球施源器行后装治疗各1次，不分先后。利用每例患者放疗时的实际CT定位资料，共40个CT定位资料，按照统一的靶区勾画标准重新勾画靶区（靶体积及危及器官）后制作近距离腔内放射治疗计划。分别统计两种施源器近距离治疗计划中靶区体积、D90、D100和膀胱、直肠体积及其D2cc。 采用独立样本t检验方法比较两种施源器在宫颈癌术后三维近距离治疗中靶区、危及器官剂量。 结果：阴道柱状施源器组和双卵圆球施源器组平均临床靶区体积分别为:（29.56±4.51）cm3、（31.68±3.16 ）cm3，差异无统计学意义(P=0.095)。柱状施源器组D90、D100分别为：（611.60±8.70）cGy、（414.38±47.16）cGy；双卵圆球施源器组D90、D100分别为：（608.19±7.30）cGy、（359.54±38.13）cGy，两组CTV D90约为 6Gy，差异无统计学意义（P=0.180）；D100差异有统计学意义（P =0.003）。柱状施源器组与双卵圆球施源器组直肠体积分别为：（53.03±10.70）cm3、（52.37±8.87）cm3，差异无统计学意义(P =0.213)；直肠D2cc分别为:（375.77±62.10）cGy、（341.57±38.43）cGy，差异有统计学意义（P=0.043）；膀胱体积分别为:（129.31±18.90）cm3、（123.14±13.15）cm3，差异无统计学意义（P=0.239）；膀胱D 2cc分别为：（391.13±62.94）cGy、（356.42±27.12）cGy，差异有统计学意义(P=0.032)。结论：宫颈癌根治术后阴道三维腔内近距离放射治疗中，与双卵圆球施源器相比，使用单通道柱状施源器靶区剂量分布更优，但膀胱、直肠受照剂量更高。因此在临床上，当直肠膀胱外照射受量较高、副反应较重可选择双卵圆球施源器，反之可选择单通道柱状施源器。

Dosimetric Study of Two Kinds of Applicators for Vaginal Three Dimensional Intracavitary Brachytherapy after Radical Hysterectomy for Cervical Cancer

Objective:To compare the dosimetric difference between single channel cylinder applicator and ovoid applica-tor in three dimensional intracavitary brachytherapy for cervical cancer patients after hysterectomy,and provide a reference for the selection of different applicators in clinical practice.Methods:A retrospective analysis was made on 20 patients with early stage cervical cancer who underwent three dimensional intracavitary brachytherapy from June to December 2018 at the oncology department in Affiliated Hospital of North Sichuan Medical College.Each patient received three dimensional intra-cavitary brachytherapy because of the indication of postoperative radiotherapy.Each patient was treated with single channel cylinder applicator and ovoid applicator in any sequence.Based on actual CT data sets of each patient during radiotherapy,a total of 40 CT data sets were used to delineate the clinical target volume and organs at risk according to unified target area de-lineation criteria,and then the brachytherapy plan was conducted.Clinical target volume,D90,D100,volume and D2cc of bladder and rectum in two brachytherapy plans with two kinds of applicators were calculated.Independent sample t-test was used to compare the doses of clinic target volume and doses of organs at risk for two applicators in three dimensional intracavi-tary brachytherapy.Results:There was no significant difference in target volume between the single channel cylinder group and the ovoid group(29.56±4.51)cm3 and(31.68±3.16)cm3(P=0.095).D90 and D100 of the single channel cylinder ap-plicator were(611.60±8.70)cGy and(414.38±47.16)cGy,and those of the ovoid applicator were(608.19±7.30)cGy and(359.54±38.13)cGy.Difference in CTV D90 was not significant(P=0.180),while that in CTV D100 was significant(P=0.003).The rectal volumes in the single channel applicator group and the ovoid applicator group were(53.03±10.70)cm3 and(52.37±8.87)cm3(P=0.832);rectal D2cc in two groups were(375.77±62.10)cGy and(341.57±38.43)cGy(P=0.043);bladder volumes in two groups were(129.31±18.90)cm3 and(123.14±13.15)cm3(P=0.239);bladder D2cc in two groups were(391.13±62.94)cGy and(356.42±27.12)cGy(P=0.032).Conclusion:In three dimensional intracavitary brachytherapy for early stage cervical cancer patients who underwent radical surgery,single channel cylinder applicator shows better target dose distribution,but higher dose for bladder and rectum compared with the ovoid applicator.In clinical prac-tice,therefore,when dose of rectum and bladder is high during the external radiation and side effects are serious,it is sug-gested to choose the ovoid applicator,otherwise single channel cylinder applicator is recommend.