Author: John J. DeMarco, Farideh Pak, Olivia Grahm C Valadie 👨🔬
Affiliation: Cedars Sinai, Cedars-Sinai, Cedars-Sinai Medical Center 🌍
Purpose: To investigate the performance of the Integral Quality Monitor (IQM) device for patient-specific QA, focusing on segment-by-segment signal evaluation compared to cumulative signal evaluation.
Methods: This study analyzed 35 clinical VMAT plans covering brain, spine, lung, and prostate indications. The VMAT plans were exported from a commercial treatment planning system to the IQM calculation database module, which calculated and stored the predicted segment-by-segment and cumulative reference signal. The VMAT plans were delivered using a conventional c-arm linac and independently measured using the IQM device for comparison with the calculated signal reference data. The corresponding average gamma pass rate using a commercial cylindrical diode array was 97.6% for the 35-plan cohort. A MATLAB routine processed treatment delivery CSV files to compute percent signal differences for segment-by-segment and cumulative signal distributions. Histogram binning was applied to determine the percentage of signal points falling within specified passing rates (the differences between predicted and measured data), using 3%, 5%, and 7% for segment-by-segment, and 1%, 2%, and 3% for cumulative distributions.
Results: The segment-by-segment analysis showed a mean absolute difference across all delivered VMAT segments of 2.0 ± 0.53% between the calculated and measured signal data. The pass rates for the 3%, 5%, and 7% criteria were 80.5%, 94.0%, and 97.5%, respectively. For the cumulative signal analysis, the mean absolute difference was 1.04 ± 0.52%, with pass rates of 57.1%, 91.7%, and 97.5% for the 1%, 2%, and 3% criteria.
Conclusion: Segment-by-segment signal evaluation in addition to cumulative signal analysis, provides a valuable metric when assessing the suitability and accuracy of the IQM system for patient-specific QA compared with conventional 2D detector arrays.