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Session: IGRT Motion Management and Tracking [Return to Session]

Surface Monitoring for Dynamic Trajectory Radiotherapy - A Feasibility Study

HA Loebner1*, J Bertholet1, D Frauchiger1, MFM Stampanoni2, P Manser1, MK Fix1, (1) Division of Medical Radiation Physics and Department of Radiation Oncology, Inselspital, Bern University Hospital, and University of Bern, Bern, Switzerland, (2) Institute for Biomedical Engineering, ETH Zuerich and PSI, Villigen, Switzerland


TU-D930-IePD-F5-3 (Tuesday, 7/12/2022) 9:30 AM - 10:00 AM [Eastern Time (GMT-4)]

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.


Treatment Verification, Image-guided Therapy, Optical Imaging


TH- External Beam- Photons: Motion management - intrafraction

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