Principal Component Analysis to Design Planning Target Volume in Oropharyngeal Cancers

PTVs remain needed to ensure target coverage in head and neck radiotherapy even with daily CT accuracy because of acquired spinal curvatures resulting in rotational displacements. A described 6D ellipsoid oriented to the reference frame can yield good coverage, but with unneeded constrictor coverage. A PCA analysis yields a PTV with equally good coverage but able to spare 70% of a constrictor.