2186 - Performance Evaluation of SGRT Technology in Conjunction with a Helical Delivery Platform for DIBH in Left-Sided Breast Cancer Treatment

Purpose/Objective(s): The use of surface-guided radiotherapy (SGRT) with deep inspiration breath hold (DIBH) on C-arm and O-ring linacs has previously been described. SGRT-based gated treatment on a helical platform represents a new opportunity for breast patients. We present the first technical evaluation of the performance of this novel integration and an analysis of treatment data.

Materials/Methods: The performance tests included surface scan volume characterization, positioning accuracy and precision of the SGRT system, and data synchronization between SGRT and delivery console. Additionally, tests were conducted to assess the accuracy and reproducibility of breath-hold levels with couch motion, as well as the system’s responsiveness to various environmental conditions. Data from 15 patient treatments were analyzed for the beam off latency (the time delay between system commands and responses) and signal reproducibility, while ensuring adequate surface coverage.

Results: Scan volume characterization verified geometric accuracy, with external isocenter measurements within ±500 mm for the lateral axis, -300 mm to +850 mm for the longitudinal axis, and -237 mm to +541 mm for the vertical axis. The SGRT system demonstrated minimal translational deviations (lateral: -0.2 mm to 0.1 mm; longitudinal: -0.1 mm to 0.2 mm; vertical: -0.1 mm to 0.1 mm) and rotational errors (pitch: 0.1°; roll: 0.15°), ensuring precise alignment crucial for DIBH treatments. DICOM import and synchronization tests validated seamless data integration, optimizing workflow efficiency. Respiration tracking highlighted consistent breath-hold reproducibility, with amplitude, timing, and surface deviations negligible (max deviation in amplitude was less than 1mm). Beam-off latency (BOL) was consistently measured at an average of 0.00377 s, ensuring rapid beam control. Surface coverage remained sufficient for breast cancer treatment, with a median signal loss distance of 45 cm. The system demonstrated resilience to ambient lighting variations, with average respiration signal deviations of 0.01–0.05 mm at breath-hold levels. Post-treatment analysis revealed stable BOL values (mean: 0.00560 s; range: 0.00411–0.00597 s) across 225 fractions, well below the vendor-specified tolerance of 0.1 s.

Conclusion: The integrated SGRT system demonstrated excellent precision, reliability, and streamlined workflow efficiency. Its auto beam hold feature stands out, prioritizing patient safety during treatment, particularly when patients experience respiratory distress or make sudden movements. This makes it an ideal choice for motion-managed radiation therapies such as DIBH. Regular QA checks are essential to maintain the parameters within the specified limits and ensure the treatment’s quality.