Bell James P, Patel Pretesh, Higgins Kristin, McDonald Mark W, Roper Justin
Department of Radiation Oncology, Simmons Comprehensive Cancer Center at the University of Texas Southwestern Medical Center, Dallas, TX.
Winship Cancer Institute of Emory University, 1356 Clifton Road NE, Building C, Atlanta, Georgia 30322.
Med Dosim. 2018;43(4):344-350. doi: 10.1016/j.meddos.2017.11.004. Epub 2017 Dec 23.
The purpose of this study was to characterize the effects of the normal tissue objective (NTO) on lung stereotactic body radiation therapy (SBRT) dose distributions. The NTO is a spatially varying constraint used in Eclipse to limit dose to normal tissues by steepening the dose gradient. However, the multitude of potential NTO setting combinations challenges optimal NTO tuning. In the present study, a broad range of NTO settings are investigated for lung SBRT treatment planning with volumetric modulated arc therapy(VMAT). Ten prior lung SBRT cases were replanned using NTO priorities of 1, 50, 100, 200, 500, and 999 in combination with fall-off values of 0.01, 0.05, 0.10, 0.15, 0.20, 0.30, 0.50, 1.00, and 5.00 mm and the automatic NTO. NTO distances to planning target volume (PTV), start dose, and end dose were 1 mm, 100%, and 10%, respectively, for all 600 plans. Prescription dose covered 95% of the PTV. The following metrics were recorded: conformity index (CI), ratio of the 50% prescription isodose volume to PTV (R), maximum dose 2 cm away from PTV (D), lung volume of ≥20 Gy (V), maximum PTV dose (PTV), and monitor units (MUs). Differences between prior plans and NTO plans were evaluated using the Wilcoxon signed-rank test. Different combinations of NTO settings resulted in wide-ranging plan quality metrics: CI (1.00 to 1.54), R (3.95 to 7.57), D (33.4% to 67.9%), V (1.66% to 2.75%), MU (1.81 cGy to 4.69 cGy), and PTV (118% to 175%). Although no settings were optimal for all metrics, a fall-off of 0.15 mm and a priority of 500 best satisfied institutional criteria. Compared with prior plans, NTO plans resulted in significantly lower R (4.00 vs 4.35, p = 0.002), lower V (1.22% vs 1.32%, p = 0.006), and higher PTV (138% vs 122%, p = 0.002). All of the prior and well-tuned NTO plans met Radiation Therapy Oncology Group (RTOG) 0813 guidelines. Lung SBRT dose distributions were characterized across a range of NTO settings. NTO plans with well-tuned settings compared favorably with prior plans.
本研究的目的是描述正常组织目标（NTO）对肺部立体定向体部放射治疗（SBRT）剂量分布的影响。NTO是Eclipse中使用的一种空间变化约束，通过使剂量梯度变陡来限制对正常组织的剂量。然而，众多潜在的NTO设置组合对优化NTO调整提出了挑战。在本研究中，针对容积调强弧形放疗（VMAT）的肺部SBRT治疗计划，研究了广泛的NTO设置。使用优先级为1、50、100、200、500和999的NTO，并结合0.01、0.05、0.10、0.15、0.20、0.30、0.50、1.00和5.00 mm的衰减值以及自动NTO，对10例既往肺部SBRT病例进行重新计划。对于所有600个计划，NTO到计划靶体积（PTV）的距离、起始剂量和结束剂量分别为1 mm、100%和10%。处方剂量覆盖PTV的95%。记录了以下指标：适形指数（CI）、50%处方等剂量体积与PTV的比值（R）、距PTV 2 cm处的最大剂量（D）、≥20 Gy的肺体积（V）、最大PTV剂量（PTV）和监测单位（MUs）。使用Wilcoxon符号秩检验评估既往计划与NTO计划之间的差异。NTO设置的不同组合导致了范围广泛的计划质量指标：CI（1.00至1.54）、R（3.95至7.57）、D（33.4%至67.9%）、V（1.66%至2.75%）、MU（1.81 cGy至4.69 cGy）和PTV（118%至175%）。虽然没有一种设置对所有指标都是最优的，但0.15 mm的衰减和500的优先级最符合机构标准。与既往计划相比？NTO计划的R显著降低（4.00对4.35，p = 0.002）、V降低（1.22%对1.32%，p = 0.006），PTV升高（138%对122%，p = 0.002）。所有既往和调整良好的NTO计划均符合放射治疗肿瘤学组（RTOG）0813指南。在一系列NTO设置中对肺部SBRT剂量分布进行了描述。设置调整良好的NTO计划与既往计划相比具有优势。 （注：原文中“Compared with prior plans, NTO plans resulted in significantly lower R (4.00 vs 4.35, p = 0.002), lower V (1.22% vs 1.32%, p = 0.006), and higher PTV (138% vs 122%, p = 0.002).”中“与既往计划相比？”这里多了个问号，疑似原文录入错误，翻译时按正确内容翻译）
