Introduction of a Reliable Software for Calculating the Gamma Index

Introduction: Gamma index is a known parameter for radiotherapy dose verification. Many free and commercial programs have been written for its calculation. However, verification of the results has been overlooked in many of them. Herein, validity of the ubiquitous gamma_index executable program written in gnuplot platform as well as simple m-files based on gamma index formulas and a more complicated m-file have been tested. Materials and Methods: The gamma indices for three measured and calculated dose distribution pairs presented in Low et al., Med. Phys., 1998 were calculated using three programs to compare with results of the published paper. They included an executable program working in gnuplot software environment (gamma_index.exe), simple implementation of the formulas by MATrix LABoratory (MATLAB) software (simple m-file) and CalcGamma MATLAB-based program distributed at github website (Geurts). The resulted gamma distributions were compared to three figures of Low et al. paper.Results: It is found that neither “gamma_index.exe” nor “simple m-file” calculated gamma indices was valid with up to 31% difference in pass rates. On the other hand, “Geurts” showed fairly good agreement with the gamma indices presented in Low et al. paper.Conclusion: Use of gamma index calculator programs like “gamma_index.exe” should strongly be prohibited without verification. Also, implementation of the gamma index formulas without enough pre-processing of the data results in invalid values. The “Geurts” program is a reliable program that can be used in its current form or it can be changed to a stand-alone executable software for use in researches and clinics.