肿瘤靶内剂量不均一很可能是空间分散放射治疗（SFRT）产生生物效应和局部肿瘤控制的原因。该研究使用商业可获得的网格准直器评估了肿瘤大小和深度不同的患者间的剂量异质性指标的间隔计划变异性。研究对14个大小从155至2161 cm3的肿瘤、等效直径从6至23 cm、深度从3至13 cm，经网格准直器基于SFRT治疗的三维异质性指标进行了研究。以6 MV光子在肿瘤中心处给予15 Gy处方剂量。推导了剂量容积直方图（DVH）指标，剂量异质性参数和峰谷剂量比率；估计了每个计划中具有不同放射敏感性的癌细胞的等效均匀剂量（EUD）。为了考虑空间分散，定义和计算了肿瘤靶区的高剂量核数密度（HCND）。 在14个计划中，DVH指标D5、D10、D50、D90和D95（覆盖目标容积的5％、10％、50％、90％和95％的剂量）变化在10％以内。D10/D90剂量比率也显示出中等一致性（范围为3.9至5.0，平均4.4）。对于放射敏感的癌细胞，EUD保持一致，范围为4.3至5.5 Gy，平均4.6 Gy；对于放射抵抗的癌细胞，EUD保持一致，范围为5.8至6.9 Gy，平均6.2 Gy。HCND在所有计划中偏差不超过20%。 基于网格准直器的SFRT提供了一致的异质性剂量分布和高剂量核密度，适用于肿瘤体积较大的计划。间隔计划的再现性和网格治疗的简易性可能对某些临床适应症和机构间的临床试验设计有用，并且其异质性指标可能有助于指导基于MLC的SFRT规划以实现类似或进一步优化的剂量分布。版权所有© 2023 Elsevier Inc.。保留所有权利。

Dose heterogeneity within a tumor target is likely responsible for the biological effects and local tumor control from spatially fractionated radiation therapy (SFRT). This study used a commercially available GRID collimator to assess the inter-plan variability of heterogeneity dose metrics in patients with various bulky tumor sizes and depths.The three-dimensional heterogeneity metrics of 14 bulky tumors, ranging from 155 to 2161 cm3 in volume, 6 to 23 cm in equivalent diameter, and 3 to 13 cm in depth, and treated with GRID collimator based SFRT were studied. A prescription dose of 15 Gy was given at the tumor center with 6 MV photons. The dose volume histogram (DVH) indices, dose heterogeneity parameters and peak/valley dose ratios were derived; the equivalent uniform doses (EUD) of cancer cells with various radiosensitivities in each plan were estimated. To account for the spatial fractionation, high dose core number density (HCND) of the tumor target was defined and calculated.Among 14 plans, the DVH indices D5, D10, D50, D90, and D95 (doses covering 5, 10, 50, 90, and 95% of the target volume) were found within 10% variation. The dose ratio of D10/D90 also showed a moderate consistency (ranging from 3.9 to 5.0, mean 4.4). The EUD was consistent, ranging from 4.3 to 5.5 Gy, mean 4.6 Gy, for radiosensitive cancer cells and from 5.8 to 6.9 Gy, mean 6.2 Gy, for radioresistant cancer cells. The HCND was within 20% among all plans.GRID collimator based SFRT delivers a consistent heterogeneity dose distribution and high dose core density across bulky tumor plans. The inter-plan reproducibility and simplicity of GRID therapy may be useful for certain clinical indications and inter-institutional clinical trial design, and its heterogeneity metrics may help guide MLC-based SFRT planning to achieve similar or further optimized dose distributions.Copyright © 2023 Elsevier Inc. All rights reserved.