Purpose: To assess the performance of a new commercial surface imaging (SI) system by analyzing intrafraction motion from the initial cohort of patients treated with frameless stereotactic radiosurgery. Aggregate data was used to analyze system performance at non-zero couch angles and when camera pods are blocked by gantry motion.
Methods: Patients were immobilized with an open face thermoplastic Encompass™ (Qfix, Avondale, PA) mask. The SI region of interest (ROI) was contoured in the treatment planning system (TPS) and exported to the SI system. Patients were aligned by kV followed with CBCT then the SI reference was captured. After treatment, linear accelerator trajectory logs were synchronized with SI logs to correlate SI reported offsets with couch and gantry positions.
Results: 58 fractions from 25 patients were monitored on an Edge linear accelerator (Varian Medical Systems, Palo Alto, CA) with IDENTIFY (Varian Medical Systems, Palo Alto, CA). The median magnitude of translational SI reported offsets at the end of treatment was 0.31 mm. The median magnitude before beam-on at non-zero couch angles was 0.57 mm. SI reported offsets were shown to increase when camera pods are blocked by the gantry with larger increases seen at non-zero couch angles.
Conclusion: SI and linear accelerator trajectory logs were used analyze intrafraction motion during frameless stereotactic radiosurgery and evaluate SI system performance. Performance is comparable to other commercially available surface imaging systems where offsets are shown to increase at non-zero couch angles and during camera pod blockage.
Funding Support, Disclosures, and Conflict of Interest: This work was funded by Varian Medical Systems.