Swallowing sparing intensity modulated radiotherapy (SW-IMRT) in head and neck cancer: Clinical validation according to the model-based approach

Purpose: The aim of this study was to clinically validate a multivariable normal tissue complication probability (NTCP) model for grade 2-4 swallowing dysfunction at 6 months after radiotherapy or chemoradiation (SWAL(M6)) in head and neck cancer patients treated with swallowing sparing intensity modulated radiotherapy (SW-IMRT) and to test if SW-IMRT resulted in a reduction of the prevalence of SWAL(M6).

Materials and methods: The primary endpoint was SWAL(M6). For all 186 patients, a standard IMRT (parotid sparing) and a SW-IMRT plan (additional constraints for swallowing organs at risk) was created. The difference in NTCP for SWALM6 (Delta NTCPSWALM6 = NTCPstandard - standard NTCPSW-IMRT) was calculated. Patients were treated with SW-IMRT. The external validation of the NTCP model was analyzed by comparing performance measures.

Results: The mean Delta NTCPSWALM6 was 4.9% (range 0.01-17.3%), with a significant lower mean predicted NTCPSW-IMRT of 22.6% (95% CI 20.2-24.9%), compared to NTCPstandard standard of 27.5% (95% CI 24.9-29.9%) (p <0.001). There was a perfect correspondence of NTCPSW-IMRT with the observed prevalence of SWAL(M6) (22.6%). The overall model performance, discrimination and 'goodness of fit' were good.

Conclusion: We externally validated the multivariable NTCP model for SWAL(M6) in SW-IMRT treated patients, showing reduced swallowing dysfunction by reducing the dose parameters included in this NTCP model. (C) 2015 The Authors. Published by Elsevier Ireland Ltd.