Department of Medical Physics, Tom Baker Cancer Centre, Calgary, AB, Canada.
Department of Physics and Astronomy, University of Calgary, Calgary, AB, Canada.
J Appl Clin Med Phys. 2020 Mar;21(3):75-86. doi: 10.1002/acm2.12827. Epub 2020 Feb 11.
In this work, the feasibility of using flattening filter free (FFF) beams in volumetric modulated arc therapy (VMAT) total body irradiation (TBI) treatment planning to decrease protracted beam-on times for these treatments was investigated. In addition, a methodology was developed to generate standardized VMAT TBI treatment plans based on patient physical dimensions to eliminate plan optimization time. A planning study cohort of 47 TBI patients previously treated with optimized VMAT ARC 6 MV beams was retrospectively examined. These patients were sorted into six categories depending on height and anteroposterior (AP) width at the umbilicus. Using Varian Eclipse, clinical 40 cm × 10 cm open field arcs were substituted with 6 MV FFF. Mid-plane lateral dose profiles in conjunction with relative arc output factors (RAOF) yielded how far a given multileaf collimator (MLC) leaf must move in order to achieve a mid-plane 100% isodose for a specific control point. Linear interpolation gave the dynamic MLC aperture for the entire arc for each patient AP width category, which was subsequently applied through Python scripting. All FFF VMAT TBI plans were then evaluated by two radiation oncologists and deemed clinically acceptable. The FFF and clinical VMAT TBI plans had similar Body-5 mm D98% distributions, but overall the FFF plans had statistically significantly increased or broader Body-5 mm D2% and mean lung dose distributions. These differences are not considered clinically significant. Median beam-on times for the FFF and clinical VMAT TBI plans were 11.07 and 18.06 min, respectively, and planning time for the FFF VMAT TBI plans was reduced by 34.1 min. In conclusion, use of FFF beams in VMAT TBI treatment planning resulted in dose homogeneity similar to our current VMAT TBI technique. Clinical dosimetric criteria were achieved for a majority of patients while planning and calculated beam-on times were reduced, offering the possibility of improved patient experience.
在这项工作中，研究了在全身调强放疗 (VMAT) 中的使用平坦化过滤无关 (FFF) 射束来降低这些治疗的长时间射线照射的可行性。此外，还开发了一种方法，根据患者的身体尺寸生成标准化的 VMAT TBI 治疗计划，以消除计划优化时间。回顾性检查了先前使用优化的 VMAT ARC 6 MV 射束治疗的 47 例 TBI 患者的计划研究队列。根据身高和脐部前后 (AP) 宽度将这些患者分为六类。使用瓦里安 Eclipse，用 6 MV FFF 替代临床 40 cm×10 cm 开野弧。中平面侧剂量分布与相对射束输出因子 (RAOF) 一起，确定了给定的多叶准直器 (MLC) 叶片必须移动多远才能在特定控制点达到中平面 100%等剂量线。线性插值为每个患者的 AP 宽度类别给出了整个射束的动态 MLC 孔径，随后通过 Python 脚本应用。然后由两位放射肿瘤学家评估所有 FFF VMAT TBI 计划，并认为临床可接受。FFF 和临床 VMAT TBI 计划的 Body-5 mm D98%分布相似，但总体而言，FFF 计划的 Body-5 mm D2%和平均肺剂量分布明显增加或变宽。这些差异不被认为具有临床意义。FFF 和临床 VMAT TBI 计划的中位射线照射时间分别为 11.07 和 18.06 分钟，FFF VMAT TBI 计划的计划时间减少了 34.1 分钟。总之，在 VMAT TBI 治疗计划中使用 FFF 射束可获得与我们目前的 VMAT TBI 技术相似的剂量均匀性。大多数患者都达到了临床剂量学标准，同时减少了计划和计算的射线照射时间，为改善患者体验提供了可能。
