Kelly Paul J, Mannarino Edward, Lewis John Henry, Baldini Elizabeth H, Hacker Fred L
Department of Radiation Oncology, Dana Farber/Brigham and Women's Cancer Center, Harvard Medical School, Boston, MA, USA.
Med Dosim. 2012 Summer;37(2):175-81. doi: 10.1016/j.meddos.2011.06.008. Epub 2011 Aug 20.
The purpose of this study was to compare conventional fixed-gantry angle intensity-modulated radiation therapy (IMRT) with RapidArc for total dural irradiation. We also hypothesize that target volume-individualized collimator angles may produce substantial normal tissue sparing when planning with RapidArc. Five-, 7-, and 9-field fixed-gantry angle sliding-window IMRT plans were generated for comparison with RapidArc plans. Optimization and normal tissue constraints were constant for all plans. All plans were normalized so that 95% of the planning target volume (PTV) received at least 100% of the dose. RapidArc was delivered using 350° clockwise and counterclockwise arcs. Conventional collimator angles of 45° and 315° were compared with 90° on both arcs. Dose prescription was 59.4 Gy in 33 fractions. PTV metrics used for comparison were coverage, V(107)%, D1%, conformality index (CI(95)%), and heterogeneity index (D(5)%-D(95)%). Brain dose, the main challenge of this case, was compared using D(1)%, Dmean, and V(5) Gy. Dose to optic chiasm, optic nerves, globes, and lenses was also compared. The use of unconventional collimator angles (90° on both arcs) substantially reduced dose to normal brain. All plans achieved acceptable target coverage. Homogeneity was similar for RapidArc and 9-field IMRT plans. However, heterogeneity increased with decreasing number of IMRT fields, resulting in unacceptable hotspots within the brain. Conformality was marginally better with RapidArc relative to IMRT. Low dose to brain, as indicated by V5Gy, was comparable in all plans. Doses to organs at risk (OARs) showed no clinically meaningful differences. The number of monitor units was lower and delivery time was reduced with RapidArc. The case-individualized RapidArc plan compared favorably with the 9-field conventional IMRT plan. In view of lower monitor unit requirements and shorter delivery time, RapidArc was selected as the optimal solution. Individualized collimator angle solutions should be considered by RapidArc dosimetrists for OARs dose reduction. RapidArc should be considered as a treatment modality for tumors that extensively involve in the skull, dura, or scalp.
本研究的目的是比较传统固定机架角度调强放射治疗（IMRT）与容积旋转调强放疗（RapidArc）用于全硬脑膜照射的效果。我们还假设，在使用RapidArc进行计划时，靶区个体化准直器角度可能会显著减少正常组织受量。生成了五野、七野和九野固定机架角度滑动窗口IMRT计划，以与RapidArc计划进行比较。所有计划的优化和正常组织约束条件均保持不变。所有计划均进行归一化处理，以使95%的计划靶区体积（PTV）至少接受100%的剂量。RapidArc使用顺时针和逆时针350°弧进行照射。将传统的45°和315°准直器角度与两弧上的90°准直器角度进行比较。剂量处方为59.4 Gy，分33次给予。用于比较的PTV指标包括靶区覆盖度、V(107)%、D1%、适形指数（CI(95)%）和不均匀性指数（D(5)%-D(95)%）。作为该病例主要挑战的脑剂量，使用D(1)%、平均剂量（Dmean）和V(5) Gy进行比较。还比较了对视交叉、视神经、眼球和晶状体的剂量。使用非常规准直器角度（两弧均为90°）可显著降低对正常脑的剂量。所有计划均实现了可接受的靶区覆盖。RapidArc计划和九野IMRT计划的均匀性相似。然而，IMRT野数减少时不均匀性增加，导致脑内出现不可接受的热点。RapidArc的适形性相对于IMRT略好。所有计划中，以V5Gy表示的低脑剂量相当。对危及器官（OARs）的剂量在临床上无显著差异。RapidArc的监测单位数较少且照射时间缩短。病例个体化的RapidArc计划优于九野传统IMRT计划。鉴于监测单位需求较低且照射时间较短，RapidArc被选为最佳方案。RapidArc剂量师应考虑采用个体化准直器角度方案来降低OARs的剂量。对于广泛累及颅骨、硬脑膜或头皮的肿瘤，应考虑将RapidArc作为一种治疗方式。
