Quantifying false positional corrections due to facial motion using SGRT with open-face Masks

Area of Science:

• Radiation Oncology
• Medical Physics
• Cancer Treatment Technology

Background:

• Open-face masks are used for intracranial and head and neck cancer treatment, offering patient comfort and comparable accuracy to closed-face masks.
• Open-face masks enable surface-guided radiation therapy (SGRT) for precise patient positioning and motion management.
• Facial motion during SGRT with open-face masks may lead to inaccurate positional corrections.

Purpose of the Study:

• To quantify the positional errors generated by SGRT systems due to facial motion when using open-face masks.
• To evaluate the impact of different mask openings (ROIs) and SGRT resolutions on positional accuracy.

Main Methods:

• Ten subjects were immobilized with open-face masks.
• Four regions of interest (ROIs) simulating different mask openings were analyzed.
• Subjects performed facial movements (eye blinks, expressions of fear/annoyance) while SGRT (C-RAD Catalyst HD) recorded isocenter shifts at standard and SRS resolutions.

Main Results:

• Facial motion, particularly eye opening/closing, caused average deviations of 0.3-0.8 mm.
• Simulated facial expressions resulted in average deviations of 1.4 mm (SRS specific) and 1.6 mm (standard resolution).
• Errors were amplified at lower SGRT resolutions and with smaller ROIs.

Conclusions:

• SGRT systems can produce false positional corrections due to facial motion with open-face masks.
• These SGRT errors increase with lower resolutions and smaller ROIs.
• Consideration of these errors is crucial for treatment planning and may necessitate additional imaging.