Feasibility of Surface-Guided Radiotherapy for Setup and Intrafraction Monitoring In Brain IMRT Using Open-Face Masks
Abstract
Purpose
To evaluate the feasibility and accuracy of surface-guided radiotherapy (SGRT) for setup and intrafraction motion monitoring in routine brain IMRT using open-face masks, and to assess whether immobilization device type affects monitoring performance.
Methods
Phantom measurements were performed using open-face thermoplastic masks mounted on either a flat baseplate or a pituitary board. A facial tracking region of interest (ROI) was defined from the upper forehead to the nasal and cheek regions, including the cheeks and area slightly above the eyebrows, while excluding the eye region to avoid motion artifacts from blinking during treatment. Initial setup was performed using SGRT surface alignment with tolerances of 0.5 mm and 0.5°. Final positioning was verified using CBCT, followed by reference surface recapture for intrafraction motion monitoring. System repeatability was evaluated using an SGRT system with advanced camera optimization enabled. Setup discrepancies between SGRT and CBCT, immobilization device dependency, and couch rotation effects were analyzed.
Results
SGRT repeatability was confirmed to be better than 0.5 mm near isocenter and remained below 0.5 mm after reference surfaces were updated. Mean translational discrepancies between SGRT-based setup and CBCT-based alignment were a maximum 1.5 mm for baseplate and 1.7 mm for pituitary board setups. After CBCT correction and reference recapture, SGRT monitoring remained stable within ±0.5 mm. Couch rotation introduced a maximum 1.5 mm additional uncertainty. No clinically meaningful difference in monitoring performance was observed between the two immobilization devices.
Conclusion
SGRT provides reliable intrafraction motion monitoring for brain IMRT with open-face masks when combined with daily CBCT and post-correction reference capture. Immobilization device type showed minimal impact on monitoring performance. These results support the feasibility of this workflow and indicate the potential for PTV margin reduction compared with current clinical practice, which will be further investigated using patient motion data prior to clinical implementation.