Threshold model

The disagreement between the TPS dose and the IC dose was computed, and thresholds of 5%, 4%, and 3% were analyzed. Thresholds of disagreement between TPS and M3D point doses (M3D threshold) were evaluated for ability to predict IC results using confusion matrices and receiver operating characteristic curve analysis.^{14 , 15} In this model, a sensitivity of 100% was preferred while maximizing specificity. For further quantitative analysis, the plans were stratified by machine and disease site.

For the 4% and 3% thresholds, the gamma index and modulation factor were also analyzed to determine how inclusion of additional metrics could improve predictive power. A Mann-Whitney U test was used to test for statistical significance of using these factors in a predictive capacity. Analysis for this model was performed in Matlab version R2019a (The Mathworks Inc, Natick, MA).