Department of Radiation Oncology, Warren Alpert Medical School of Brown University, Rhode Island Hospital, 593 Eddy Street, Providence, Rhode Island 02903, USA.
Med Phys. 2011 May;38(5):2419-23. doi: 10.1118/1.3576106.
The purpose of this study is to evaluate the dosimetric effect of carbon fiber couches (CFCs) on delivered skin dose as well as to explore potential venues for its minimization for volumetric modulated arc (VMAT) treatments.
A carbon fiber couch (BrainLab) was incorporated in Pinnacle treatment planning system (TPS) by autocontouring. A retrospective investigation on five lung and five prostate patient plans was performed. Targets and organs at risk (OARs), together with a 0.3 cm thick skin contour interfacing the CFC, were outlined in each plan. For each patient, two VMAT plans were generated: a single arc with 6 MV photon energy and two or three arcs with 18 MV photon energy for the posterior arc(s) and 6 MV energy for the anterior arc (mixed energy plans). Both plans for each patient case were normalized such that 95% of the PTV was covered by the same prescription dose, ranging from 7600 to 7800 cGy. For each patient, the prescription doses were escalated to the maximum allowed by the OAR constraints. CFC bolus effects on skin doses were tallied by the highest dose to 1% of skin volume.
With the utilization of higher energy photons for the posterior arcs, the statistically significant differences in skin dose between the two plans were as high as 34% of the prescribed dose, where surface doses changed on average from 3800 to 2940 cGy for 6 MV and mixed energy plans, respectively. In addition, skin doses in excess of 68% and 80% of the prescription doses for mixed and 6 MV energy plans, respectively, were observed in individual cases.
The presented findings indicate that mixed energy VMAT plans would result in a substantial skin sparing of more than approximately 34% compared to VMAT plans with only 6 MV arc(s). Additionally, the high skin doses in some cases (81% of the prescription dose) suggest that in hypofractionated SRS/SRT treatments, the carbon fiber couch effects on skin doses need to be evaluated when arc delivery is considered as a treatment option.
本研究旨在评估碳纤维躺椅（CFC）对皮肤剂量的剂量学影响，并探讨最小化容积调强弧形治疗（VMAT）中皮肤剂量的潜在途径。
通过自动轮廓，在 Pinnacle 治疗计划系统（TPS）中加入碳纤维躺椅。对 5 例肺癌和 5 例前列腺患者的计划进行回顾性研究。在每个计划中，勾画了靶区和危及器官（OAR），以及与 CFC 相接的 0.3cm 厚的皮肤轮廓。对于每个患者，生成了两个 VMAT 计划：一个 6MV 光子能量的单弧和一个或两个 18MV 光子能量的后弧，以及一个 6MV 能量的前弧（混合能量计划）。每个患者的两个计划都进行归一化，使 95%的 PTV 被相同的处方剂量覆盖，剂量范围为 7600 至 7800cGy。对于每个患者，处方剂量都根据 OAR 限制允许的最大值进行了递增。通过 1%皮肤体积的最高剂量来计算 CFC 垫的皮肤剂量。
利用更高能量的光子进行后弧治疗，两种计划之间的皮肤剂量差异高达处方剂量的 34%，其中表面剂量分别从 6MV 和混合能量计划的 3800cGy 平均变化到 2940cGy。此外，在个别情况下，混合能量和 6MV 能量计划的皮肤剂量分别超过了处方剂量的 68%和 80%。
本研究结果表明，与仅使用 6MV 弧的 VMAT 计划相比，混合能量 VMAT 计划可使皮肤剂量显著减少 34%以上。此外，在某些情况下（处方剂量的 81%）皮肤剂量较高，这表明在分次立体定向放射治疗（SRS/SRT）中，当弧形治疗被视为一种治疗选择时，需要评估碳纤维躺椅对皮肤剂量的影响。
