Novel Calibration Approach for Surface Guided Radiotherapy in Patients with Diverse Skin Reflectance: An Indian Experience
Abstract
Purpose
Surface Guided Radiation Therapy (SGRT) systems are increasingly used for patient positioning and motion management in radiotherapy. However, their performance may be influenced by variations in patient skin tone, as differences in optical absorption and reflectance can affect surface registration accuracy. This study evaluated the performance of C-RAD SGRT systems using custom-designed anthropomorphic phantoms representing diverse skin tones commonly observed in the Indian population, aiming to ensure optimal setup accuracy and equitable treatment safety for all patients.
Methods
Three anthropomorphic phantoms were prepared to simulate light, medium, and dark Indian skin tones, using distinct shades of commercially available makeup foundation (Lakme). Each phantom was assessed using two SGRT systems—Sentinel (single-camera) during CT simulation and Catalyst HD (three-camera) in the treatment room. For Sentinel, threshold and integration time were systematically varied, while for Catalyst HD, gain and integration time were adjusted to optimize performance. Surface reconstruction quality was evaluated based on image continuity, absence of voids, and adequacy of topographic detail required for accurate surface tracking.
Results
Compared to vendor-recommended default settings, the Sentinel system required up to 3.8-fold longer integration times for light and medium-tone phantoms, and up to 6-fold longer for the dark-tone phantom to achieve complete surface reconstruction. Threshold values below 300 produced noisy or incomplete surfaces, whereas a fixed threshold of 300 yielded consistent performance across all tones. For Catalyst HD, increasing gain to 567% and extending integration time (2× for light, ≥3× for medium and dark tones) significantly improved registration fidelity.
Conclusion
This India-specific phantom-based investigation highlights that SGRT accuracy is influenced by skin tone, with darker tones necessitating optimized camera settings. Adjusting integration and gain parameters enhances surface detection reliability, supporting safe and precise radiotherapy for diverse Indian patients. Further clinical validation is warranted to assess workflow implications and treatment accuracy.