Author: Richard Lesieur, Olivia Magneson, David E. Solis, Sotirios Stathakis 👨🔬
Affiliation: Louisiana State University, Mary Bird Perkins Cancer Center 🌍
Purpose: This study evaluates the deliverability and precision of multileaf collimator (MLC) positioning in treatment plans generated by two different Treatment Planning Systems (TPS), Monaco and Pinnacle, on Elekta linear accelerators. The dosimetric impact of the MLC errors was then evaluated to determine the significance of varying root mean squared error (RMSE) between TPS.
Methods: The cohort consisted of 21 patients treated for various oncological indications, including head and neck, lung, prostate, and abdomen. Utilizing high-resolution log files, the Root Mean Square Error (RMSE) associated with MLC positioning was quantified and analyzed along with additional metrics such as treatment durations and MLC travel distances. Five prostate/pelvis treatment plans were modified to incorporate MLC positioning errors using homemade code, and the dose was recalculated within the Monaco TPS. Gamma analysis with varying criteria, including a 20% dose threshold was employed to compare the recalculated total dose.
Results: Comparative analysis indicated that plans optimized by Monaco consistently demonstrated a lower RMSE compared to those generated by Pinnacle, suggesting superior accuracy in MLC positioning. This enhanced precision is particularly crucial in treatment sites requiring meticulous spatial accuracy, such as head and neck regions, where even minimal deviations may significantly impact treatment outcomes. No statistically significant differences were found in the mean gamma indices or gamma pass rates between the two TPS, as determined by T-test analysis.
Conclusion: These findings underscore the necessity of refining TPS optimization algorithms and establishing rigorous MLC positioning tolerances for volumetric modulated arc therapy (VMAT). Despite the differences in error magnitude, no statistically significant variations were observed in gamma pass rates or mean gamma indices between the initial dose calculation and the logfile-recalculated plan.