Non-coplanar volumetric-modulated arc therapy (VMAT) for craniopharyngiomas reduces radiation doses to the bilateral hippocampus: a planning study comparing dynamic conformal arc therapy, coplanar VMAT, and non-coplanar VMAT.
Non-coplanar volumetric-modulated arc therapy (VMAT) for craniopharyngiomas reduces radiation doses to the bilateral hippocampus: a planning study comparing dynamic conformal arc therapy, coplanar VMAT, and non-coplanar VMAT.
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DOI：
10.1186/s13014-016-0659-x
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发表时间：
2016-06-23
期刊：
影响因子：
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通讯作者：
Hiraoka M
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文献类型：
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作者：
Uto M;Mizowaki T;Ogura K;Hiraoka M
最近的研究表明，辐射诱导的海马区损伤在脑肿瘤患者的神经认知功能损害中起着重要作用，对于颅咽管瘤患者来说，使用现代计划方法来保留海马区可能是重要的。由于双侧海马区与颅咽管瘤患者的计划靶区体积(PTV)位于同一水平，使用非共面射束似乎有可能降低对海马区的剂量。虽然最近有报道将非共面射束用于颅内恶性肿瘤的体积调制弧疗(VMAT)，但在颅咽管瘤患者中，使用非共面弧线的VMAT(NcVMAT)和仅使用共面弧线的VMAT(CoVMAT)之间的剂量学比较尚未见报道。我们进行了一项计划研究，比较了动态适形弧疗(DCAT)、coVMAT和ncVMAT对PTV、海马体和其他危险器官(OAR)的剂量分布。为10例颅咽管瘤患者创建了DCAT、coVMAT和ncVMAT计划。处方剂量为52.2Gy29次，每个PTV的99%被90%的处方剂量覆盖。最大剂量控制在规定剂量的107%以下。制定了CoVMAT和ncVMAT计划，以满足以下标准：对海马区的剂量最小，对OAR的剂量与DCAT相似或更低。DCAT/coVMAT/ncVMAT的平均剂量分别为15.4/10.8/6.5Gy2Gy分次至双侧海马区体积的40%。NcVMAT的EQD2(40%河马)为7.3Gy.这是Gondi等人定义的预测认知障碍的阈值。三种计划对正常脑组织的平均剂量和适形指数相似，而coVMAT和ncVMAT的均质性指数明显好于DCAT。对于颅咽管瘤患者，NcVMAT比DCAT和CoVMAT更合适。NcVMAT显著减少了双侧海马区的辐射剂量(至DCAT的50%)，而不增加对正常脑组织和其他OAR的剂量。本文的在线版本(doi：10.1186/s130140160659-x)包含补充材料，授权用户可以使用。
Recent studies suggest that radiation-induced injuries to the hippocampus play important roles in compromising neurocognitive functioning for patients with brain tumors and it could be important to spare the hippocampus using modern planning methods for patients with craniopharyngiomas. As bilateral hippocampus are located on the same level as the planning target volume (PTV) in patients with craniopharyngioma, it seems possible to reduce doses to hippocampus using non-coplanar beams. While the use of non-coplanar beams in volumetric-modulated arc therapy (VMAT) of malignant intracranial tumors has recently been reported, no dosimetric comparison has yet been made between VMAT using non-coplanar arcs (ncVMAT) and VMAT employing only coplanar arcs (coVMAT) among patients with craniopharyngiomas. We performed a planning study comparing dose distributions to the PTV, hippocampus, and other organs at risk (OAR) of dynamic conformal arc therapy (DCAT), coVMAT, and ncVMAT. DCAT, coVMAT, and ncVMAT plans were created for 10 patients with craniopharyngiomas. The prescription dose was 52.2 Gy in 29 fractions, and 99 % of each PTV was covered by 90 % of the prescribed dose. The maximum dose was held below 107 % of the prescribed dose. CoVMAT and ncVMAT plans were formulated to satisfy the following criteria: the doses to the hippocampus were minimized, and the doses to the OAR were similar to or lower than those of DCAT. The mean equivalent doses in 2-Gy fractions to 40 % of the volumes of the bilateral hippocampus [EQD2(40%hippos)] were 15.4/10.8/6.5 Gy for DCAT/coVMAT/ncVMAT, respectively. The EQD2(40%hippos) for ncVMAT were <7.3 Gy, which is the threshold predicting cognitive impairment, as defined by Gondi et al.. The mean doses to normal brain tissue and the conformity indices were similar for the three plans, and the homogeneity indices were significantly better for coVMAT and ncVMAT compared with DCAT. NcVMAT is more appropriate than DCAT and coVMAT for patients with craniopharyngiomas. NcVMAT significantly reduces radiation doses to the bilateral hippocampus (to 50 % that of the DCAT) without increasing the doses to normal brain tissue and other OAR. The online version of this article (doi:10.1186/s13014-016-0659-x) contains supplementary material, which is available to authorized users.