Clinical and dosimetric predictors of physician and patient reported xerostomia following intensity modulated radiotherapy for nasopharyngeal cancer – A prospective cohort analysis

•Significant proportion of patients still experienced long term xerostomia with IMRT.•Despite the use of IMRT, none of the patients met the recommended dose constraint of parotid glands.•Dose-effect relationships between xerostomia and the parotid glands were not observed in this study.•The incidence of physician-rated xerostomia was consistently lower than patient-reported xerostomia across all time points.•Sophisticated radiotherapy technique such as proton therapy may be able to better spare the salivary glands.