The observed salivary excretion factor (SEF) data and the fitted dose–response curve for the normal tissue complication probability of the incidence of grade 3
xerostomia (salivary flow ≤45% relative to pre-RT) at 1 year after radiotherapy as a function of the mean dose to the spared parotid gland. Dashed lines show 95% confidence intervals for the model fit to the SEF data (solid line). The squares represented the group patient mean doses in bins 4-Gy width. (All individual dose data points were used in the NTCP fitting).