Daniela Falco Maria, Giancaterino Stefano, D'Andrea Marco, Gimenez De Lorenzo Ramon, Trignani Marianna, Caravatta Luciana, Di Carlo Clelia, Di Biase Saide, Allajbej Albina, Genovesi Domenico
Department of Radiation Oncology, "G. D'Annunzio" University of Chieti, SS. Annunziata Hospital, Chieti, Italy.
Laboratory of Medical Physics and Expert Systems, National Cancer Center Institute Regina Elena, Rome, Italy.
J Appl Clin Med Phys. 2018 Jan;19(1):86-93. doi: 10.1002/acm2.12216. Epub 2017 Nov 10.
Volumetric Modulated Arc Therapy (VMAT) techniques for fractioned stereotactic brain radiotherapy (FSBRT) can achieve highly conformal dose distribution to intracranial lesions. However, they can potentially increase the dose to hippocampus (H) causing neurocognitive toxicity during the first four months after irradiation. The purpose of this study was to assess the feasibility of hippocampal-sparing (HS) treatment plans in 22 patients with brain metastasis treated with VMAT technique. Firstly, we retrospectively analyzed hippocampal doses in all 22 VMAT original (not hippocampal-sparing, NHS) plans. Plans with hippocampal dose exceeding constraints (9 out of 22) were re-planned considering dose constraints on the hippocampus (H) and on hippocampal avoidance zone (HAZ) generated using 5 mm isotropic margin to the hippocampus. Conformity (CI) and homogeneity indexes (HI) on the target and MUs, were maintained as close as possible to the original plans. Mean CI and CI obtained were: 0.79 ± 0.11 and 0.81 ± 0.10, respectively (P = 0.75); mean HI and HI were 1.05 ± 0.02 and 1.04 ± 0.01 respectively (P = 0.72). In both sets of plans, the mean MU values were similar: 1033 ± 275 and 1022 ± 234 for NHS and HS respectively. In HS plans, the mean hippocampal dose was decreased by an average of 35%. After replanning, the D (21.3 Gy) for HAZ and H was met by 45% (4/9) and 78% (7/9) of the NHS plans, respectively. The worst results were obtained for cases with target volumes extention closer than 12 mm to H, because of the difficulty to spare hippocampus without compromising target coverage. After replanning D constraint value (7.3 Gy) was met by all the 9 NHS plans. In conclusion, this study suggests that an hippocampal-sparing approach to FSBRT is feasible resulting in a decrease in the dose to the hippocampus without any loss in conformity or increase in treatment time.
容积调强弧形放疗（VMAT）技术用于分次立体定向脑放疗（FSBRT）时，可实现对颅内病变高度适形的剂量分布。然而，它们可能会增加海马体（H）的剂量，从而在照射后的头四个月内导致神经认知毒性。本研究的目的是评估在22例接受VMAT技术治疗的脑转移瘤患者中实施海马体保护（HS）治疗计划的可行性。首先，我们回顾性分析了所有22个VMAT原始（非海马体保护，NHS）计划中的海马体剂量。对于海马体剂量超过限制的计划（22个中有9个），在考虑海马体（H）以及使用距海马体各向同性5 mm边缘生成的海马体避让区（HAZ）的剂量限制后重新进行计划。靶区的适形度（CI）和均匀性指数（HI）以及机器跳数（MUs）尽可能保持与原始计划接近。获得的平均CI和CI分别为：0.79±0.11和0.81±0.10（P = 0.75）；平均HI和HI分别为1.05±0.02和1.04±0.01（P = 0.72）。在两组计划中，平均MU值相似：NHS计划和HS计划分别为1033±275和1022±234。在HS计划中，平均海马体剂量平均降低了35%。重新计划后，NHS计划中有45%（4/9）和78%（7/9）分别满足了HAZ和H的D（21.3 Gy）要求。对于靶区体积延伸至距H小于12 mm的病例，结果最差，因为在不影响靶区覆盖的情况下难以保护海马体。重新计划后，所有9个NHS计划均满足D约束值（7.3 Gy）。总之，本研究表明，FSBRT的海马体保护方法是可行的，可降低海马体剂量，且不会导致适形度降低或治疗时间增加。
