Room: AAPM ePoster Library
Purpose: To investigate the utility of long-term monitoring of patient-specific delivery parameters using trajectory logs.
Methods: A subset of patients treated on two linear accelerators were monitored for four months using trajectory logs in addition to conventional quality assurance methods including pre-treatment measurements and weekly chart checks. The study focused on patients treated with IMRT, VMAT, and Dynamic Conformal Arc (DCA) planning and delivery techniques. A broad range of treatment sites were evaluated including Brain, H&N, Thorax, Abdomen, and Pelvis. An in-house trajectory log reader was developed and customized to parse all trajectory log files for a given patient and compare the linac delivery parameters versus the DICOM treatment planning file. The software parses the delivery control points from the trajectory logs (20 msec temporal resolution) and compares the daily control point snapshots with the treatment planning control points.
Results: The trajectory logs for 155 patients were processed and compared against the original DICOM treatment plan export file. Synthetic fluence maps were generated for each treatment fraction and all treatment fields using the MLC leaf positions from the trajectory logs and compared against the corresponding DICOM plan fluence maps. The average gamma pass rate across all treatment fields was 93.3±2.1% (1% dose difference, 1mm DTA, 10% dose cutoff) for 10 H&N patients. The maximum standard deviation was less than 0.1% for the day-to-day MLC leaf trajectory variations using the treatment plan versus trajectory log gamma estimate. Treatment delivery beam-holds are also evaluated in the context of motion management and linac gating.
Conclusion: delivery control points were extracted from the trajectory logs for 155 patients treated over a 4-month period. Daily gamma calculations comparing trajectory log versus DICOM fluence maps and linac beam-hold monitoring for DIBH patients are presented as examples for long-term monitoring of daily trajectory log files