Treatment Interrupted Trajectory Log Analysis Via Fully Automated Interpolation of the Treatment Planning System’s Plan Parameters
Abstract
Purpose
Interrupted patient treatments that are split into multiple partially delivered trajectory log files for a given field may be most susceptible to Linac delivery errors. The AAPM TG-100 recommends independent QA checks to prevent the most hazardous failure modes. We have developed an independent software analysis program called “TrajectoryLogMagik” that compares the Linac treatment delivery directly with the expected plan parameters of the treatment planning system (TPS), effectively independently verifying Linac delivery.
Methods
The gantry, collimator, jaws, and MLC positions at each control point in the TPS are linearly interpolated to match the Linac’s delivered fractional control points, directly comparing the TPS parameters with the delivered machine parameters every 20 milli-seconds. Correct field and trajectory log file order is found relative to the expected TPS fields, with multiple trajectory logs “stitched” together for analysis. Automated analysis is performed daily for all delivered patient fractions by finding and using the exported TPS plan files and associated trajectory log files generated during treatment. Pass/Fail results are recorded into an Excel spreadsheet where failing plans can be further analyzed by the software. All code was written in MATLAB R2023a and works for the Varian TrueBeam and Ethos/Halcyon Linacs for both interrupted and non-interrupted plans, and for automated, non-automated, and partially-automated plans.
Results
Over 120 patient treatments are analyzed each day at our center, with approximately 2% exhibiting some type of treatment interruption during beam delivery. Over the last 4 weeks, most discrepancies have been located at beam interrupted interfaces, with maximum MU, gantry/collimator, and jaw/MLC deviations of 0.3MUs, 1.4 degrees, and 1.2mm, respectively. Unexpected beam holds (actual delivered minus MU beam holds) were frequent, potentially affecting plan deliverability.
Conclusion
TrajectoryLogMagik, a fully automated code, independently verifies Linac treatment delivery directly with the expected values of the TPS, including interrupted treatment plans.