3种全脑放疗技术对中耳剂量学研究

Dosimetric study on middle ear with three whole-brain radiotherapy techniques

目的比较脑转移瘤全脑放射治疗(WBRT)3种放疗技术对中耳的剂量学差异,对比3种放疗技术在改善靶区剂量和保护中耳腔和咽鼓管峡部的优劣势。方法选取2018年7月1日—2019年8月1日我院收治的30例脑转移瘤患者,分别设计固定野调强放疗(ff-IMRT)计划、容积旋转调强放疗(VMAT)和三维适形放疗(3DCRT)计划,要求处方剂量(40 Gy)覆盖95%的计划靶区(PTV)。对比分析3组计划的靶区和危及器官剂量学参数、机器跳数等差异。结果ff-IMRT计划的适形指数(0.93±0.02)优于VMAT计划(0.89±0.01)和3DCRT计划(0.73±0.03),差异有统计学意义(P<0.05);ff-IMRT、VMAT和3DCRT 3种计划的均匀指数分别为(0.05±0.01)、(0.08±0.1)、(0.08±0.01),差异无统计学意义(P>0.05);梯度指数分别为(1.77±0.1)、(1.61±0.07)、(1.39±0.08),差异有统计学意义(P<0.05);机器跳数分别为(1551.97±85.05)、(303.7±24.28)、(226.2±2.5),差异有统计学意义(P<0.05)。ff-IMRT、VMAT和3DCRT 3种计划中耳腔最大剂量点(D_(max))分别为ff-IMRT(2557.54±477.39)cGy、VMAT(3107.9±362.28)cGy、3DCRT(4055.37±71.45)cGy;咽鼓管峡部D_(max)分别为ff-IMRT(2425±380.4)cGy、VMAT(2902.4±526.3)cGy、3DCRT(3862.7±135.9)cGy,差异均有统计学意义(P<0.05)。结论在全脑放射治疗中,ff-IMRT和VMAT与3DCRT相比明显减少了双侧中耳腔和咽鼓管峡部的照射剂量;而VMAT与ff-IMRT相比,明显减少机器跳数、降低了机器损耗,WBRT时推荐使用VMAT技术。

Objective This study aims to compare the advantages and disadvantages of the three techniques in improving the target volume dose and protecting the auris media cavity and eustachian tube isthmus region by investigating the dosimetric differences of three whole-brain radiotherapy techniques.Methods Thirty patients with whole brain metastases were randomly selected to design fixed field intensity modulated radiotherapy(ff-IMRT)plan,volumetric arc modulated therapy(VMAT)and three-dimensional conformal radiotherapy(3DCRT)plan,and to meet a 95%PTV prescription dose(40 Gy).The dosimetric parameters and monitor units of the target volume and organ at risk(OAR)in the three groups of treatment plans were compared and analyzed.Results The Conformity Index(CI)of the ff-IMRT plan(0.93±0.02)was better than the VMAT plan(0.89±0.01)and the 3DCRT plan(0.73±0.03),respectively,and the difference was statistically significant(P<0.05).The Homogeneity Index(HI)of the three plans were ff-IMRT(0.05±0.01)、VMAT(0.08±0.1)and 3DCRT(0.08±0.01),respectively,and the difference was not statistically significant(P>0.05).The Gradient Index(GI)were ffIMRT(1.77±0.1),VMAT(1.61±0.07),3DCRT(1.39±0.08),respectively.The difference was statistically significant(P<0.05).The monitor units(MU)were ff-IMRT(1551.97±85.02),VMAT(303.7±24.28)and 3DCRT(226.2±2.5),respectively,the difference was statistically significant(P<0.05).The D_(max) of the middle ear of the three plans were ff-IMRT(2557.54±477.39)cGy,VMAT(3107.9±362.28)cGy,3DCRT(4055.37±71.45)cGy,respectively.The D_(max) of the eustachian tube isthmus were ff-IMRT(2425±380.4)cGy,VMAT(2902.4±526.3)cGy and 3DCRT(3862.7±135.9)cGy the difference were statistically significant(P<0.05).Conclusion In whole-brain radiotherapy,ff-IMRT and VMAT significantly reduced the dose of the bilateral middle ear cavities and eustachian tube isthmus compared with 3DCRT.VMAT is recommended for WBRT for reducing the number of monitor units significantly.