Volumetric changes of the parotid gland during IMRT based on mid-treatment imaging: implications for parotid stem cell sparing strategies in head and neck cancer.

The radiation dose to the PGSC region did not show stronger association with patient-reported xerostomia compared to that of whole PG, possibly due to considerable anatomical changes identified at mid-treatment. This shift in the size and position of the PG warrants adaptive planning strategies to evaluate the true benefit of parotid stem cell sparing.