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

Victoria Bry, Anna Laura Licon, James McCulloch, Neil Kirby, Pamela Myers, Daniel Saenz, Sotirios Stathakis, Niko Papanikolaou, Karl Rasmussen

Research output: Contribution to journalArticlepeer-review

11 Scopus citations


Purpose: Studies have evaluated the viability of using open-face masks as an immobilization technique to treat intracranial and head and neck cancers. This method offers less stress to the patient with comparable accuracy to closed-face masks. Open-face masks permit implementation of surface guided radiation therapy (SGRT) to assist in positioning and motion management. Research suggests that changes in patient facial expressions may influence the SGRT system to generate false positional corrections. This study aims to quantify these errors produced by the SGRT system due to face motion. Methods: Ten human subjects were immobilized using open-face masks. Four discrete SGRT regions of interest (ROIs) were analyzed based on anatomical features to simulate different mask openings. The largest ROI was lateral to the cheeks, superior to the eyebrows, and inferior to the mouth. The smallest ROI included only the eyes and bridge of the nose. Subjects were asked to open and close their eyes and simulate fear and annoyance and peak isocenter shifts were recorded. This was performed in both standard and SRS specific resolutions with the C-RAD Catalyst HD system. Results: All four ROIs analyzed in SRS and Standard resolutions demonstrated an average deviation of 0.3 ± 0.3 mm for eyes closed and 0.4 ± 0.4 mm shift for eyes open, and 0.3 ± 0.3 mm for eyes closed and 0.8 ± 0.9 mm shift for eyes open. The average deviation observed due to changing facial expressions was 1.4 ± 0.9 mm for SRS specific and 1.6 ± 1.6 mm for standard resolution. Conclusion: The SGRT system can generate false positional corrections for face motion and this is amplified at lower resolutions and smaller ROIs. These errors should be considered in the overall tolerances and treatment plan when using open-face masks with SGRT and may warrant additional radiographic imaging.

Original languageEnglish (US)
Pages (from-to)172-183
Number of pages12
JournalJournal of Applied Clinical Medical Physics
Issue number4
StatePublished - Apr 2021


  • SGRT
  • SRS
  • immobilization
  • radiation therapy
  • surface guided imaging

ASJC Scopus subject areas

  • Instrumentation
  • Radiation
  • Radiology Nuclear Medicine and imaging


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