Estimating PTV margins in head and neck stereotactic ablative radiation therapy (SABR) through target site analysis of positioning and intrafractional accuracy.

HN-SABR PTV margins should be optimized by target site. PTV margins of 1.5-2mm may be sufficient in the skull base, while 2-2.5mm may be necessary for neck and mucosal targets. When using ExacTrac, skull base sites show significantly fewer uncertainties throughout the treatment process, while neck/mucosal targets may require the addition of CBCT to account for positioning errors and internal organ motion.