Correction of image-guided radiotherapy and intrafraction motion using ExacTrac dynamic for head and neck cancer patients.

Daily cone-beam computed tomography (CBCT) based image-guided radiotherapy (IGRT) with six degrees of freedom (6DOF) is standard for head and neck cancer. We retrospectively analyzed 669 sessions from 20 patients, using CBCT guided 6DOF couch corrections followed by ExacTrac Dynamic adjustments. Surface-guided radiotherapy (SGRT) continuously monitored intrafraction motion, triggering verification images and couch shifts when tolerances were exceeded. Pitch and roll deviations were linked to translational misalignments up to 3 mm. SGRT prompted repositioning in 100 sessions (15%), although nearly half of these movements were false positives. This demonstrates SGRT's value as a complementary, non-invasive tool for intrafraction monitoring.