Table 3.

Overview of studies on NTCP models for dysphagia grade II-IV according to the RTOG/EORTC Late Radiation Toxicity Scoring system.

Reference	Time point, mo	Quality criteria for NTCP models										Level of evidence
		RT technique	Study design	Analysis	No. of patients	No. of events	AUC	Calibration tested	Internal validation	External validation	Individual NTCP estimation possible
Current study	6	Primary IMRT	Prospective	External validation	813	242	0.81	Yes	Yes	Yes	Yes	1b
Christianen 2012 [15]	6	Primary 3DCRT and IMRT	Prospective	Multivariable	354	NM	0.80	No	Yes	No	Yes	3
Christianen 2016 [16]a	6	SW-IMRT	Prospective	External validation	186	59	0.75	Yes	No	Yes	Yes	2a
Blanchard 2016 [17]b	6	Protons	Prospective	External validation	89	27	0.70	Yes	Yes	Yes	Yes	1a
Dirix 2009 [18]	Variable	Primary 3DCRT and IMRT	Cross-sectional	Multivariable	53	14	NM	No	No	No	No	4
Mazzola 2014 [19]	Acute	Primary IMRT	Retrospective	Univariable	53	46	NM	No	No	No	No	4
	3					23	NM	No	No	No	No	4
	Late					13	NM	No	No	No	No	4

Abbreviations: NTCP, Normal Tissue Complication Probability; RTOG/EORTC, Radiation Therapy Oncology Group / European Organization for Research and Treatment; RT, radiation therapy; AUC, Area Under the Curve; IMRT, intensity-modulated radiation therapy; 3DCRT, 3-dimensional conformal radiation therapy; NM, Not mentioned; SW-IMRT, swallowing-sparing IMRT; DVH, dose-volume histogram.

^aThis study used the NTCP model from Christianen 2012 [15] to guide treatment planning optimization using the DVH parameters of the NTCP model. The study showed that the observed toxicity rates were lower with SW-IMRT and that the observed toxicity rates corresponded very well with the predicted rates based on the NTCP model.

^bThis study externally validated the NCTP model from Christianen 2012 [15] among patients treated with protons.