Development of NTCP models for head and neck cancer patients treated with three- dimensional conformal radiotherapy for xerostomia and sticky saliva: The role of dosimetric and clinical factors  Ivo Beetz, Cornelis Schilstra, Fred R. Burlage, Phil W. Koken, Patricia Doornaert, Henk P. Bijl, Olga Chouvalova, C. René Leemans, Geertruida H. de Bock, Miranda E.M.C. Christianen, Bernard F.A.M. van der Laan, Arjan Vissink, Roel J.H.M. Steenbakkers, Johannes A. Langendijk  Radiotherapy and Oncology  Volume 105, Issue 1, Pages 86-93 (October 2012) DOI: 10.1016/j.radonc.2011.05.010 Copyright © 2011 Elsevier Ireland Ltd Terms and Conditions

Fig. 1 Paerson correlation coefficients between the ipsi- and contralateral parotid gland. Part of the correlation matrix. Strong correlations between two variables (>0.8) are colored in red. Very strong correlations within and between ipsi- and contralateral salivary glands were observed and, therefore, analyses were carried out with pairs of ipsi- and contralateral glands, to avoid multicollinearity. Radiotherapy and Oncology 2012 105, 86-93DOI: (10.1016/j.radonc.2011.05.010) Copyright © 2011 Elsevier Ireland Ltd Terms and Conditions

Fig. 2 Average likelihood for bootstrapping technique for each number of selected variables in the multivariate logistic regression analysis for each model order. Best model performance is observed with a model order with the highest average of total likelihood of bootstrap predictions. For, respectively, xerostomia and sticky saliva the best model performance was seen with three and four selected variables. Radiotherapy and Oncology 2012 105, 86-93DOI: (10.1016/j.radonc.2011.05.010) Copyright © 2011 Elsevier Ireland Ltd Terms and Conditions