Zhang Isabella, Antone Jeff, Li Jenny, Saha Shyamali, Riegel Adam C, Vijeh Lili, Lauritano Joe, Marrero Mihaela, Salas Sussan, Schulder Michael, Zinkin Heather, Goenka Anuj, Knisely Jonathan
Department of Radiation Medicine, Northwell Health, Hofstra Northwell School of Medicine, Lake Success, New York.
Department of Radiation Medicine, Northwell Health, Hofstra Northwell School of Medicine, Lake Success, New York.
Pract Radiat Oncol. 2017 May-Jun;7(3):183-189. doi: 10.1016/j.prro.2017.01.012.
Our purpose was to evaluate hippocampal doses and target volume coverage with and without hippocampal sparing when treating multiple brain metastases using various stereotactic radiosurgery (SRS) platforms.
We selected 10 consecutive patients with 14 separate treatments who had been treated in our department for 3 to 10 brain metastases and added hippocampal avoidance contours. All 14 treatments were planned with GammaPlan for Gamma Knife, Eclipse for single isocenter volumetric modulated arc therapy (VMAT), TomoTherapy Treatment Planning System (TPS) for TomoTherapy, and MultiPlan for CyberKnife. Initial planning was performed with the goal of planning target volume coverage of V100 ≥95% without hippocampal avoidance. If the maximum hippocampal point dose (Dmax) was <6.6 Gy in a single fraction and <40% of the hippocampi received ≤4.5 Gy, no second plan was performed. If either constraint was not met, replanning was performed with these constraints.
There was a median of 6 metastases per plan, with an average total tumor volume of 7.32 mL per plan. The median hippocampal Dmax (in Gy) without sparing averaged 1.65, 9.81, 4.38, and 5.46, respectively (P < .0001). Of 14 plans, 3 Gamma Knife and CyberKnife plans required replanning, whereas 13 VMAT and 8 TomoTherapy plans required replanning. The hippocampal constraints were not achievable in 1 plan on any platform when the tumor was bordering the hippocampus. The mean volume of brain receiving 12 Gy (in mL), which has been associated with symptomatic radionecrosis, was 23.57 with Gamma Knife, 76.77 with VMAT, 40.86 with CyberKnife, and 104.06 with TomoTherapy (P = .01). The overall average conformity indices for all plans ranged from 0.36 to 0.52.
Even with SRS, the hippocampi can receive a considerable dose; however, if the hippocampi are outlined as organs of risk, sparing these structures is feasible in nearly all situations with all 4 platforms, without detriment to target coverage, and should be considered in all patients undergoing SRS for multiple brain metastases.
Hippocampi play an important role in memory, and sparing of these structures in whole brain radiation can improve neurocognitive outcomes. The hippocampi are not routinely spared when using stereotactic radiosurgery. We evaluated the incidental dose to the hippocampi when treating multiple brain metastases and sought to examine if hippocampal sparing is feasible without detriment to target coverage. We found that hippocampal sparing is possible without affecting coverage or conformality in most cases across treatment platforms.
我们的目的是评估使用各种立体定向放射外科（SRS）平台治疗多发脑转移瘤时，有或没有海马体保留情况下的海马体剂量和靶区覆盖情况。
我们选择了10例连续患者，共进行了14次单独治疗，这些患者在我们科室接受了3至10个脑转移瘤的治疗，并添加了海马体避让轮廓。所有14次治疗均使用GammaPlan进行伽玛刀治疗计划、使用Eclipse进行单等中心容积调强弧形放疗（VMAT）计划、使用TomoTherapy治疗计划系统（TPS）进行托姆刀治疗计划以及使用MultiPlan进行射波刀治疗计划。初始计划的目标是在不进行海马体避让的情况下，计划靶区覆盖率V100≥95%。如果单次分割中最大海马体点剂量（Dmax）<6.6 Gy且≤4.5 Gy的海马体体积<40%，则不进行第二次计划。如果未满足任何一个限制条件，则在这些限制条件下重新进行计划。
每个计划的转移瘤中位数为6个，每个计划的平均总肿瘤体积为7.32 mL。不进行保留时，海马体Dmax中位数（单位：Gy）分别平均为1.65、9.81、4.38和5.46（P <.0001）。在14个计划中，3个伽玛刀和射波刀计划需要重新计划，而13个VMAT计划和8个托姆刀计划需要重新计划。当肿瘤靠近海马体时，在任何平台上的1个计划中都无法实现海马体限制条件。与有症状放射性坏死相关的接受12 Gy照射的脑平均体积（单位：mL），伽玛刀为23.57，VMAT为76.77，射波刀为40.86，托姆刀为104.06（P =.01）。所有计划的总体平均适形指数范围为0.36至0.52。
即使使用SRS，海马体也可能接受相当大的剂量；然而，如果将海马体勾勒为危险器官，在几乎所有情况下，使用所有4种平台保留这些结构都是可行的，且不损害靶区覆盖，对于所有接受SRS治疗多发脑转移瘤的患者都应予以考虑。
海马体在记忆中起重要作用，在全脑放疗中保留这些结构可改善神经认知结果。使用立体定向放射外科时，海马体通常不被保留。我们评估了治疗多发脑转移瘤时海马体的附带剂量，并试图研究在不损害靶区覆盖的情况下保留海马体是否可行。我们发现，在大多数情况下，跨治疗平台保留海马体是可行的，且不影响覆盖或适形性。
