Room: Exhibit Hall | Forum 5
Purpose: Gamma analysis is a widely used QA metric to assess the difference between dose distributions. The goal of this investigation is to evaluate the accuracy of the implemented gamma analysis method.
Methods: An automated dose comparison tool was developed using the gamma index pioneered by Low et al with a limited search optimization. Three sample patient cases with doses generated by a treatment planning system and a second-check Monte Carlo dosimetry algorithm were used. A manual spreadsheet calculation of the gamma index was performed at 3 points on each patient, sampled in high and low dose gradients. The distance to agreement (DTA) and dose difference (DD) criteria used were 3mm/3%, 2mm/2% and 1mm/1% for each point. Also, an artificial dose distribution shaped as a spherical â€œbullseyeâ€? was scaled to 97%, 98%, and 99% of the original dose, and shifts of 1mm, 2mm, and 3mm were applied to each dose. The scaling and shift components were used to assess the DD and DTA criteria, respectively. Gamma analyses with multiple DTA/DD criteria were performed between the original and modified dose distributions, and results were assessed qualitatively.
Results: For all points and DTA/DD criteria assessed, spreadsheet calculation verified that the gamma calculation in the automated dose comparison tool produced results accurate to a high degree of precision (<0.0001). The gamma comparisons between the bullseye dose distribution and modified versions of this distribution yielded 3D gamma maps that visually matched those that were expected.
Conclusion: This study demonstrates the accuracy of the gamma validation tool, providing confidence in its use for comparing doses, such as those generated by a treatment planning system and second-check algorithm.
Funding Support, Disclosures, and Conflict of Interest: All authors are employed by MIM Software Inc. or MIM Software Brussels BVBA.