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

Abstract

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 conformai 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 ( GT) were ff-IMRT (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 (1 551.97 ± 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 (2 557.54 ± 477.39) cGy, VMAT (3 107.9 ± 362.28) cGy, 3DCRT (4 055.37 ± 71.45) cGy, respectively. The D _max of the eustachian tube isthmus were ff-IMRT (2 425 ± 380.4) cGy, VMAT (2 902.4 ± 526.3) cGy and 3DCRT (3 862.7 ± 135.9) cGy, the difference were statistically significant ( P < 0.05).

Conclusion In whole-brain radiotherapy, ff-IMRT and VMAT significantly reduced fhe dose of fhe bilateral middle ear cavities and eustachian tube isthmus compared with 3DCRT. VMAT is recommended for WBRT for reducing the number of monitor units significantly.

Abstract

摘要： 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 日一2019 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 (1 551.97 ± 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 (2 557.54 ± 477.39) cGy、VMAT (3 107.9 ± 362.28) cGy、3DCRT (4 055.37 ± 71.45) cGy; 咽鼓管峡部 D _max 分别为 ff-IMRT (2 425 ± 380.4) cGy、VMAT (2 902.4 ± 526.3) cGy、3DCRT (3 862.7 ± 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。