The impacts of dose rate in sliding window intensity modulated radiation therapy quality assurance

Background: The present study aims to compare the impacts of dose rate in intensity-modulated radiation therapy (IMRT) plan delivery by using the gamma agreement between the calculated and measured doses by pretreatment quality assurance (QA). Materials and Methods: Ten nasopharynx cancer patients who underwent IMRT treatment were included in this study. The treatment plans were performed using Varian DHX eclipse treatment planning system (TPS) version 15.1. and the QA plans were generated for the dose rates of 300, 400, 500 and 600 MU/min. All measurements were performed by aS1000 Electronic Portal Imaging Device (Epid) integrated into Varian DHX linear accelerator and 2D array detector. The dose distribution was evaluated with gamma area histograms (GAHs) generated using different γ criteria (2%/2 mm and 3%/3 mm) for dose agreement and distance to agreement parameters. Statistical analyses were evaluated by using Mann-Whitney Test and a p-value of p <0.05 was considered to be significant. Results: There was a significant decrease in the percentage gamma pass rate when the dose rate was increased from 300 MU/min to 600 MU/min (p<0.05). There was a significant difference between Epid and Epiqa for all dose rates (p<0.05). The total number of MU was correlated to the dose rate. When comparing MU from 300 MU/min to 600 MU/min dose rate, it was observed that the MU of IMRT plans increaed as the dose rate was increased. Conclusion: In this study, we have demonstrated that IMRT delivery using sliding window method is affected by the dose rate.