Department of Radiation Oncology, Faculty of Medicine, Ondokuz Mayıs University, Samsun, 55139, Turkey.
BMC Cancer. 2023 Jun 6;23(1):515. doi: 10.1186/s12885-023-11033-8.
Our purpose was to ensure that the dose constraints of the organs at risk (OARs) were not exceeded while increasing the prescription dose to the planning target volume (PTV) from 45 to 50.4 Gray (Gy) with the dynamic intensity-modulated radiotherapy (IMRT) technique. While trying for this purpose, a new dynamic IMRT technique named 90° angled collimated dynamic IMRT (A-IMRT) planning was developed by us.
This study was based on the computed tomography data sets of 20 patients with postoperatively diagnosed International Federation of Gynecology and Obstetrics stage 2 endometrial carcinoma. For each patient, conventional dynamic IMRT (C-IMRT, collimator angle of 0° at all gantry angles), A-IMRT (collimator angle of 90° at gantry angles of 110°, 180°, 215°, and 285°), and volumetric modulated arc therapy (VMAT) were planned. Planning techniques were compared with parameters used to evaluate PTV and OARs via dose-volume-histogram analysis using the paired two-tailed Wilcoxon's signed-rank test; p < 0.05 was considered indicative of statistical significance.
All plans achieved adequate dose coverage for PTV. Although the technique with the lowest mean conformality index was A-IMRT (0.76 ± 0.05) compared to both C-IMRT (0.79 ± 0.04, p = 0.000) and VMAT (0.83 ± 0.03, p = 0.000), it protected the OARs especially the bladder (V45 = 32.84 ± 2.03 vs. 44.21 ± 6.67, p = 0.000), rectum (V30 = 56.18 ± 2.05 vs. 73.80 ± 4.75, p = 0.000) and both femoral heads (V30 for right = 12.19 ± 1.34 vs. 21.42 ± 4.03, p = 0.000 and V30 for left = 12.58 ± 1.48 vs. 21.35 ± 4.16, p = 0.000) better than C-IMRT. While the dose constraints of the bladder, rectum and bilateral femoral heads were not exceeded in any patient with A-IMRT or VMAT, they were exceeded in 19 (95%), 20 (100%) and 20 (100%) patients with C-IMRT, respectively.
OARs are better protected when external beam radiotherapy is applied to the pelvis at a dose of 50.4 Gy by turning the collimator angle to 90° at some gantry angles with the dynamic IMRT technique in the absence of VMAT.
我们的目的是在使用动态调强放疗（IMRT）技术将计划靶区（PTV）的处方剂量从 45 提高到 50.4 戈瑞（Gy）的同时，确保危及器官（OAR）的剂量限制不被超过。为此，我们开发了一种新的动态 IMRT 技术，称为 90°角准直动态 IMRT（A-IMRT）计划。
这项研究基于 20 名术后诊断为国际妇产科联合会（FIGO）分期 2 期子宫内膜癌的患者的计算机断层扫描数据集。对于每个患者，我们分别制定了常规动态 IMRT（C-IMRT，在所有机架角度下准直器角度为 0°）、A-IMRT（在机架角度为 110°、180°、215°和 285°时准直器角度为 90°）和容积调强弧形治疗（VMAT）计划。使用配对双侧 Wilcoxon 符号秩检验通过剂量-体积-直方图分析比较了 PTV 和 OAR 的参数；p<0.05 表示具有统计学意义。
所有计划都实现了 PTV 的足够剂量覆盖。尽管 A-IMRT 的平均适形度指数最低（0.76±0.05），低于 C-IMRT（0.79±0.04，p=0.000）和 VMAT（0.83±0.03，p=0.000），但它特别保护了 OAR，尤其是膀胱（V45=32.84±2.03 比 44.21±6.67，p=0.000）、直肠（V30=56.18±2.05 比 73.80±4.75，p=0.000）和两个股骨头（右侧 V30=12.19±1.34 比 21.42±4.03，p=0.000，左侧 V30=12.58±1.48 比 21.35±4.16，p=0.000）。而在 A-IMRT 或 VMAT 中，没有一个患者的膀胱、直肠和双侧股骨头的剂量限制被超过，但在 C-IMRT 中，分别有 19（95%）、20（100%）和 20（100%）患者的剂量限制被超过。
在没有 VMAT 的情况下，通过在某些机架角度将准直器角度旋转至 90°，使用动态 IMRT 技术将骨盆的外照射剂量提高至 50.4 Gy 时，OAR 得到更好的保护。
