External validation of three dimensional conformal radiotherapy based NTCP models for patient-rated xerostomia and sticky saliva among patients treated with intensity modulated radiotherapy

3D-CRT based models for patient-rated xerostomia and sticky saliva among head and neck cancer patients treated with primary radiotherapy or chemoradiation turned out to be less valid for patients treated with IMRT. The main message from these findings is that models developed in a population treated with a specific technique cannot be generalised and extrapolated to a population treated with another technique without external validation.