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Abstract：
OBJECTIVE: Modern radiotherapy practices typically report the absorbed dose (D) within the 5% relative isodose volume (i.e., the therapeutic dose region) to an accuracy of 3%-5%. Gamma-index analysis, the most commonly used method to evaluate dosimetric accuracy, has low sensitivity to discrepancies that occur outside of this region. The objective of this study was to develop an evaluation method with high sensitivity across dose distributions spanning three orders of magnitude.
METHODS: We generalized the gamma index to include an additional criterion, the absolute absorbed dose difference, specifically for the low-dose region (i.e., D ≤ 5%). We also proposed a method to objectively select the appropriate magnitudes for relative-dose-difference, absolute-dose-difference, and distance-to-agreement criteria. We demonstrated the generalized gamma-index method by first finding the appropriate generalized gamma-index agreement criteria at an interval of specified passing rates. Next, we used the generalized gamma index to evaluate one-, two-, and three-dimensional absorbed dose distributions in a water-box phantom and voxelized patient geometry.
RESULTS: Generalized gamma-index passing rates for one-, two-, and three-dimensional dose distributions were 55.4%, 44.5%, and 8.9%, respectively. Traditional gamma-index passing rates were 100%, 97.8%, and 96.4%, respectively. These results reveal that the generalized method has adequate sensitivity in all regions (i.e., therapeutic and low dose). Additionally, the algorithmic determination of triplets of agreement criteria revealed that they are strong functions of the specified passing rate.
CONCLUSIONS: The major finding of this work is that the proposed method provides an objective evaluation of the agreement of dose distributions spanning three orders of magnitude. In particular, this generalized method correctly characterized dosimetric agreement in the low-dose region, which was not possible by traditional methods. The proposed algorithmic selection of agreement criteria decreased subjectivity and requirements of user judgment and skill. This method could find utility in a variety of applications including dose-algorithm development and translation.
METHODS: We generalized the gamma index to include an additional criterion, the absolute absorbed dose difference, specifically for the low-dose region (i.e., D ≤ 5%). We also proposed a method to objectively select the appropriate magnitudes for relative-dose-difference, absolute-dose-difference, and distance-to-agreement criteria. We demonstrated the generalized gamma-index method by first finding the appropriate generalized gamma-index agreement criteria at an interval of specified passing rates. Next, we used the generalized gamma index to evaluate one-, two-, and three-dimensional absorbed dose distributions in a water-box phantom and voxelized patient geometry.
RESULTS: Generalized gamma-index passing rates for one-, two-, and three-dimensional dose distributions were 55.4%, 44.5%, and 8.9%, respectively. Traditional gamma-index passing rates were 100%, 97.8%, and 96.4%, respectively. These results reveal that the generalized method has adequate sensitivity in all regions (i.e., therapeutic and low dose). Additionally, the algorithmic determination of triplets of agreement criteria revealed that they are strong functions of the specified passing rate.
CONCLUSIONS: The major finding of this work is that the proposed method provides an objective evaluation of the agreement of dose distributions spanning three orders of magnitude. In particular, this generalized method correctly characterized dosimetric agreement in the low-dose region, which was not possible by traditional methods. The proposed algorithmic selection of agreement criteria decreased subjectivity and requirements of user judgment and skill. This method could find utility in a variety of applications including dose-algorithm development and translation.
摘要：
目的：现代放射治疗实践通常在5％相对等剂量体积内报告吸收剂量（D）（即，治疗剂量区域)的准确度为3%-5%。伽马指数分析，最常用的评估剂量测定准确性的方法，对该区域以外发生的差异的敏感性较低。这项研究的目的是开发一种跨三个数量级的剂量分布的高灵敏度评估方法。
方法：我们将伽马指数推广为包括附加标准，绝对吸收剂量差，特别是针对低剂量区域(即，D≤5%)。我们还提出了一种客观地选择相对剂量差的适当幅度的方法，绝对剂量差，和协议距离标准。我们通过首先在指定的通过率间隔内找到适当的广义伽马指数一致性标准来证明广义伽马指数方法。接下来,我们使用广义伽马指数来评估一个，two-,和三维吸收剂量分布在水盒体模和体素化的患者几何形状。
结果：1-，two-,三维剂量分布为55.4%，44.5%,和8.9%，分别。传统的伽马指数通过率是100%,97.8%,和96.4%，分别。这些结果表明，广义方法在所有区域都具有足够的灵敏度(即，治疗和低剂量)。此外,协议标准三元组的算法确定表明，它们是指定通过率的强大函数。
结论：这项工作的主要发现是，所提出的方法对跨三个数量级的剂量分布的一致性提供了客观评估。特别是,这种广义方法正确地表征了低剂量区域的剂量学一致性，这在传统方法中是不可能的。提出的协议标准的算法选择降低了主观性和用户判断和技能的要求。该方法可以在包括剂量算法开发和翻译的各种应用中找到效用。
方法：我们将伽马指数推广为包括附加标准，绝对吸收剂量差，特别是针对低剂量区域(即，D≤5%)。我们还提出了一种客观地选择相对剂量差的适当幅度的方法，绝对剂量差，和协议距离标准。我们通过首先在指定的通过率间隔内找到适当的广义伽马指数一致性标准来证明广义伽马指数方法。接下来,我们使用广义伽马指数来评估一个，two-,和三维吸收剂量分布在水盒体模和体素化的患者几何形状。
结果：1-，two-,三维剂量分布为55.4%，44.5%,和8.9%，分别。传统的伽马指数通过率是100%,97.8%,和96.4%，分别。这些结果表明，广义方法在所有区域都具有足够的灵敏度(即，治疗和低剂量)。此外,协议标准三元组的算法确定表明，它们是指定通过率的强大函数。
结论：这项工作的主要发现是，所提出的方法对跨三个数量级的剂量分布的一致性提供了客观评估。特别是,这种广义方法正确地表征了低剂量区域的剂量学一致性，这在传统方法中是不可能的。提出的协议标准的算法选择降低了主观性和用户判断和技能的要求。该方法可以在包括剂量算法开发和翻译的各种应用中找到效用。
