Khoo V S, Oldham M, Adams E J, Bedford J L, Webb S, Brada M
Neuro-oncology Unit, The Institute of Cancer Research and the Royal Marsden NHS Trust, Sutton, Surrey, United Kingdom.
Int J Radiat Oncol Biol Phys. 1999 Sep 1;45(2):415-25. doi: 10.1016/s0360-3016(99)00213-8.
Intensity-modulated radiotherapy (IMRT) offers the potential to more closely conform dose distributions to the target, and spare organs at risk (OAR). Its clinical value is still being defined. The present study aims to compare IMRT with stereotactically guided conformal radiotherapy (SCRT) for patients with medium size convex-shaped brain tumors.
Five patients planned with SCRT were replanned with the IMRT-tomotherapy method using the Peacock system (Nomos Corporation). The planning target volume (PTV) and relevant OAR were assessed, and compared relative to SCRT plans using dose statistics, dose-volume histograms (DVH), and the Radiation Therapy Oncology Group (RTOG) stereotactic radiosurgery criteria.
The median and mean PTV were 78 cm3 and 85 cm3 respectively (range 62-119 cm3). The differences in PTV doses for the whole group (Peacock-SCRT +/-1 SD) were 2%+/-1.8 (minimum PTV), and 0.1%+/-1.9 (maximum PTV). The PTV homogeneity achieved by Peacock was 12.1%+/-1.7 compared to 13.9%+/-1.3 with SCRT. Using RTOG guidelines, Peacock plans provided acceptable PTV coverage for all 5/5 plans compared to minor coverage deviations in 4/5 SCRT plans; acceptable homogeneity index for both plans (Peacock = 1.1 vs. SCRT = 1.2); and comparable conformity index (1.4 each). As a consequence of the transaxial method of arc delivery, the optic nerves received mean and maximum doses that were 11.1 to 11.6%, and 10.3 to 15.2% higher respectively with Peacock plan. The maximum optic lens, and brainstem dose were 3.1 to 4.8% higher, and 0.6% lower respectively with Peacock plan. However, all doses remained below the tolerance threshold (5 Gy for lens, and 50 Gy for optic nerves) and were clinically acceptable.
The Peacock method provided improved PTV coverage, albeit small, in this group of convex tumors. Although the OAR doses were higher using the Peacock plans, all doses remained within the clinically defined threshold and were clinically acceptable. Further improvements may be expected using other methods of IMRT planning that do not limit the treatment delivery to transaxial arcs. Each IMRT system needs to be individually assessed as the paradigm utilized may provide different outcomes.
调强放射治疗（IMRT）有可能使剂量分布更紧密地贴合靶区，并保护危及器官（OAR）。其临床价值仍在确定中。本研究旨在比较IMRT与立体定向引导适形放射治疗（SCRT）用于治疗中等大小凸形脑肿瘤患者的效果。
对5例采用SCRT计划的患者，使用孔雀系统（诺莫斯公司）通过IMRT断层治疗方法重新进行计划。评估计划靶体积（PTV）和相关OAR，并使用剂量统计、剂量体积直方图（DVH）以及放射治疗肿瘤学组（RTOG）立体定向放射外科标准与SCRT计划进行比较。
PTV的中位数和平均值分别为78 cm³和85 cm³（范围62 - 119 cm³）。全组PTV剂量差异（孔雀系统 - SCRT ±1标准差）在最小PTV时为2% ±1.8，在最大PTV时为0.1% ±1.9。孔雀系统实现的PTV均匀性为12.1% ±1.7，而SCRT为13.9% ±1.3。根据RTOG指南，孔雀系统计划为所有5/5的计划提供了可接受的PTV覆盖，相比之下，5/4的SCRT计划存在较小的覆盖偏差；两个计划的均匀性指数均可接受（孔雀系统 = 1.1，SCRT = 1.2）；适形指数相当（均为1.4）。由于采用了轴向弧形照射方法，孔雀系统计划使视神经接受的平均剂量和最大剂量分别高出11.1%至11.6%和10.3%至15.2%。孔雀系统计划使晶状体最大剂量和脑干剂量分别高出3.1%至4.8%和低0.6%。然而，所有剂量均保持在耐受阈值以下（晶状体为5 Gy，视神经为50 Gy），且在临床上是可接受的。
在这组凸形肿瘤中，孔雀系统方法提供了改善的PTV覆盖，尽管改善幅度较小。虽然使用孔雀系统计划时OAR剂量较高，但所有剂量仍在临床定义的阈值内，且在临床上是可接受的。使用不局限于轴向弧形照射的其他IMRT计划方法可能会有进一步改善。每个IMRT系统都需要单独评估，因为所采用的模式可能会提供不同的结果。
