Brito Delgado A, Cohen D, Eng T Y, Stanley D N, Shi Z, Charlton M, Gutiérrez A N
Department of Radiation Oncology, School of Medicine, Cancer Therapy & Research Center, The University of Texas Health Science Center San Antonio, San Antonio, TX 78229, USA.
Department of Radiation Oncology, School of Medicine, Cancer Therapy & Research Center, The University of Texas Health Science Center San Antonio, San Antonio, TX 78229, USA; Department of Radiation Oncology, Miami Cancer Institute, 8900 North Kendall Drive, Miami, FL 33176, USA.
Med Dosim. 2018;43(1):1-10. doi: 10.1016/j.meddos.2017.07.009. Epub 2017 Dec 6.
There has been growing interest in the use of stereotactic body radiotherapy (SBRT) technique for the treatment of cervical cancer. The purpose of this study was to characterize dose distributions as well as model the target dose fall-off for intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT) delivery techniques using 6 and 10 MV photon beam energies. Fifteen (n = 15) patients with non-bulky cervical tumors were planned in Pinnacle with a Varian Novalis Tx (HD120 MLC) using 6 and 10 MV photons with the following techniques: (1) IMRT with 10 non-coplanar beams (2) dual, coplanar 358° VMAT arcs (4° spacing), and (3) triple, non-coplanar VMAT arcs. Treatment volumes and dose prescriptions were segmented according to University of Texas Southwestern (UTSW) Phase II study. All plans were normalized such that 98% of the planning target volume (PTV) received 28 Gy (4 fractions). For the PTV, the following metrics were evaluated: homogeneity index, conformity index, D, D, D, and dose fall-off parameters. For the organs at risk (OARs), D, D, D, V, V, V, V, and V were evaluated for the bladder, bowel, femoral heads, rectum, and sigmoid. Statistical differences were evaluated using a Friedman test with a significance level of 0.05. To model dose fall-off, expanding 2-mm-thick concentric rings were created around the PTV, and doses were recorded. Statistically significant differences (p < 0.05) were noted in the dose fall-off when using 10 MV and VMAT, as compared with IMRT. VMAT improved the bladder V, V, and V, and the bowel V and V. All fitted regressions had an R ≥ 0.98. For cervical SBRT plans, a VMAT approach offers a steeper dose fall-off outside of the target volume. Faster dose fall-off was observed in smaller targets as opposed to medium and large targets, denoting that OAR sparing is dependent on target size. These improvements are further pronounced with the use of 10-MV photons.
立体定向体部放射治疗（SBRT）技术在宫颈癌治疗中的应用越来越受到关注。本研究的目的是使用6和10MV光子束能量，对调强放射治疗（IMRT）和容积调强弧形治疗（VMAT）的剂量分布进行特征描述，并对靶区剂量下降进行建模。在Pinnacle中，使用瓦里安Novalis Tx（HD120 MLC）对15例（n = 15）非体积较大的宫颈肿瘤患者进行计划，采用6和10MV光子及以下技术：（1）10个非共面射野的IMRT；（2）双共面358°VMAT弧形（4°间隔）；（3）三非共面VMAT弧形。根据德克萨斯大学西南医学中心（UTSW）II期研究对治疗体积和剂量处方进行分割。所有计划均进行归一化，使98%的计划靶区体积（PTV）接受28 Gy（4次分割）。对于PTV，评估以下指标：均匀性指数、适形指数、D、D、D以及剂量下降参数。对于危及器官（OAR），评估膀胱、肠道、股骨头、直肠和乙状结肠的D、D、D、V、V、V、V和V。使用Friedman检验评估统计学差异，显著性水平为0.05。为了对剂量下降进行建模，在PTV周围创建厚度为2mm的同心扩展环，并记录剂量。与IMRT相比，使用l0MV和VMAT时在剂量下降方面存在统计学显著差异（p < 0.05）。VMAT改善了膀胱的V、V和V，以及肠道的V和V。所有拟合回归的R≥0.98。对于宫颈SBRT计划，VMAT方法在靶区体积外提供了更陡的剂量下降。与中、大靶区相比，在较小靶区观察到更快的剂量下降，这表明对危及器官的保护取决于靶区大小。使用10MV光子时，这些改善更为明显。
