Room: Exhibit Hall | Forum 4
Purpose: The multileaf collimator (MLC) system is considered a vital component to the accuracy of intensity-modulated radiotherapy (IMRT), and even more so when used in succession with the gantry for volumetric modulated arc therapy (VMAT). This study reviews over 8,000 patient VMAT treatments using machine log files form two Elekta Versa HD machines on MLC performance and compares results against TG-142 recommendations.
Methods: Elekta Log files were collected from the machines over the past 2 years and decoded into MATLABÂ®. Delivery data was extracted for beam on with a resolution of 0.04 sec. For both MLC banks and individual leaves, the root mean square (RMS) error, maximum, and mean leaf speeds were calculated. These values in addition, to gantry angles, gantry speeds, and treatment time were reviewed for correlations.
Results: Most of the plans were found to have a mean leaf speed of 9.8 mm/s with a correlated RMSE of 0.47 mm. An increase with RMSE error of 0.035 mm was found for every 1 mm/s increase in mean leaf speed. Specific gantry angles did not play a role in increasing overall BANK RMSE. Gantry speed was not found to directly correlate with Bank RMS error, however a generalized area of error was found around 4-5.5 deg/sec with a bank RMSE ranging between 0.3 to 0.85 mm. Over 90% of the plans had a delivery time between 55-75 sec with bank RMSE between 0.25-0.85, however a hot spot for Bank RMSE was found localized around 0.36-0.54 mm.
Conclusion: Reducing maximum leaf speed should help improve MLC performance for VMAT treatments. Gantry angle or speed do not show any significant correlation to increasing or reducing RMS Error. The Agility MLC system falls within the tolerances of TG-142, however greater tolerances can be achieved by reducing mean MLC speeds.
Not Applicable / None Entered.