Streamlined Quality Assurance Workflow for Linac Based SRS Using an Elekta Versa 6FFF Beam
Abstract
Purpose
Accurate precise planning and delivery of linac-based stereotactic radiosurgery (SRS) can be technically challenging and stressful. Thus, it is important to develop a streamlined clinical workflow to increase efficiency, accuracy and precision of the treatment
Methods
An Elekta Versa HD linac equipped with 6 MV FFF beam, Agility MLC, and Hexapod couch was commissioned for SRS treatments. During commissioning, relative output factors (ROFs), PDDs and beam profiles were measured and cross validated using three different detectors. Agreement to the treatment planning system (TPS) was evaluated using 1mm/2% gamma analysis. KV-imaging isocenter was calibrated to coincide with the 6FFF radiation isocenter. The IROC SRS anthropomorphic phantom was irradiated for end-to-end testing. Prior to patient treatment, a mask fit, CT- and MR-simulation scans were acquired. A custom MIM workflow was developed to automatically standardize and register multiple MR sequences. Targets and OARs were delineated and transferred to the Monaco TPS for planning. A 1.5mm margin was selected for single iso treatment and 2mm margin for multitarget, multi-iso planning to account for treatment uncertainties. A dry run was scheduled to evaluate real-time patient monitoring using VisionRT and verify couch clearance. Patient‐specific QA was performed using Sun Nuclear SRS-Mapcheck. Agreement between imaging- and radiation-isocenters was evaluated using a Sun Nuclear Multi-Met Winston-Lutz (MM_WL) cube.
Results
Monaco TPS calculations demonstrated gamma passing rates >95% for field sizes as small as 0.6×0.6cm² compared to measured data. ROFs for all field sizes were within 2% of the TPS model. The WL-test confirmed field-target coincidence prior to patient treatment. Patient-specific QA measurements achieved gamma passing rates >95%. Implementation of the dry-run and MM_WL provides sufficient time to resolve issues related to gantry clearance, couch wobbling, or real-time monitoring prior to treatment.
Conclusion
A streamlined workflow was developed to ensure precise, safe, and high-quality SRS delivery with an Elekta Versa 6FFF Beam