Exhibit Hall | Forum 5
Purpose: To assess the feasibility and accuracy of time-resolved surface monitoring during dynamic trajectory radiotherapy (DTRT) for table rotation verification and intrafraction motion monitoring.
Methods: DTRT extends VMAT by dynamic table and collimator rotation during beam-on. A tri-camera-based surface-monitoring-system (SMS, IDENTIFY™, Varian Medical Systems) was used during delivery of five different DTRT plans, each covering a full gantry rotation with different table rotations.First, four spheres beside a head phantom were used to monitor and record table-rotation-angle at 5 Hz. The accuracy of the time-resolved recorded table-rotation-angle in SMS-logfiles was assessed by comparison with the values recorded in the treatment machine logfile using root-mean-square-error (RMSE). Second, a moving phantom with three styrofoam spheres was used for intrafraction motion monitoring. Peak-to-peak amplitude was 1.5 cm (vertical), 0.4 cm (longitudinal) and 8° (pitch-rotation). Motion along the other axes was below 1 mm/1°. Accuracy was quantified by comparing motion during DTRT delivery to motion recorded with static table (reference) using RMSE. The experiment was repeated with the phantom rotated by 90° to explore the lateral and roll axes.
Results: Time-resolved monitoring was available without loss of signal at any gantry-table angle combination for the investigated DTRT plans and phantoms. The RMSE of the table-rotation-angle monitoring was 0.32° for the first experiment.The RMSE for motion monitoring in the second experiment was 0.49 mm (vertical), 0.27 mm (longitudinal), 0.37° (pitch-rotation), and, for the 90° rotated phantom 0.70 mm (vertical), 0.28 mm (lateral), 0.52° (roll-rotation). Monitoring of the phantom rotation (reference motion below 1° peak-to-peak) due to table rotation was compared to treatment machine recorded table rotation resulting in a RMSE of 0.21° and 0.22° with the rotated phantom.
Conclusion: SMS was successfully applied to verify table rotation and to monitor intrafraction motion during DTRT with sub-mm and sub-degree accuracy for the cases considered.
Funding Support, Disclosures, and Conflict of Interest: This work was partially supported by Varian Medical Systems.