A note on the interpretation of the gamma evaluation index

7th International Conference on 3D Radiation Dosimetry

Ceberg, Crister^1

Medical Radiation Physics, Department of Clinical Sciences Lund, Lund University, Lund, Sweden^1

关键词: Absorbed dose distribution;    Chi-squared distribution;    Clinical radiotherapy;    Degree of freedom;    Evaluation index;    Gamma distribution;    Standard deviation;    Statistical significance;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/444/1/012082/pdf
DOI  :  10.1088/1742-6596/444/1/012082

来源: IOP

【 摘 要 】

The gamma evaluation method has become the gold standard for the comparison between measured and calculated absorbed dose distributions. However, test criteria and failure rate tolerance levels have hitherto normally been based on empirical evidence, rather than rigorous statistical analysis. In this work, it is proposed that the gamma-evaluation method could be reinterpreted such that the absorbed dose difference and distance-to-agreement criteria are replaced by the standard deviations of the associated uncertainties. By comparison between absorbed dose calculations and simulated measurements for clinically realistic test cases in 1D and 2D, it is then shown that the resulting squared gamma distribution follows a chi-squared distribution with one degree of freedom. This result can be used to test the statistical significance of measured deviations, and to determine proper failure rate tolerance levels in clinical radiotherapy quality control.