Simulated study relating dose-volume histogram metrics to three-dimensional gamma analysis results

This study aims to investigate the relationship between the three-dimensional gamma index (3DGI) results and its clinical significance, proposing a correlation between changes in dose values in the dose-volume histogram (DVH) of the evaluated structures and 3DGI percentages of approval. In this study, we created 30 plans by including 1 mm displacement errors in the lateral, vertical, and longitudinal axes of each table, and compared them to a simulated, error-free treatment plan for prostate cancer. The plans were made in a commercial treatment planning system, using 6MV Varian 120-leaf multileaf collimators (MLC) linear accelerators and intensity modulated radiation therapy sliding window technique. We used a calculation algorithm-based MATLAB programming to evaluate the 3DGI analysis of fluence maps. The acceptance criteria were 3%/2 mm, 10% dose threshold, and 95% gamma passing rate. We compared 3DGI results with differences in structures DVH. DVH metrics versus 3DGI analysis showed a correlation between the percentage of point’s approval and planning target volume (PTV) coverage, presenting a degree of agreement of 0.85%, 0.96%, and 0.94% in the longitudinal, lateral, and vertical axes, respectively. In summary, it was possible to establish a linear relationship between the percentage of points approved in the 3DGI analysis and the PTV dose. A similar behavior was also observed in bladder and rectum DVH, but for these structures, the relationship was not the same in the three displaced axes.