128 The number of patients with swallowing dysfunction per time of assessment are shown in Table 2 as well, either because of WST failure or because a number above the cut-off value was reached. Both a WST failure and a score above the cut-off value were reported in 16 patients. The prevalence of swallowing dysfunction is estimated to be 19.1% at baseline, 21.6% at M3, 19.2% at M6, 14.8% at M12, and 13.9% at M24. Factors associated with number of swallows Linear mixed model analysis revealed that tumor site, sex, and tumor stage were not associated with the number of swallows, and were therefore removed from the final model. The course of number of swallows was significantly associated with age, and there was a significant interaction between treatment modality and timing of assessment, as shown in Table 3. Higher age was associated with a higher number of swallows (+0.07 more swallows per increasing year). Number of swallows of patients with surgery alone were comparable to number of swallows of patients that received surgery and adjuvant (C)RT: there was an increase in number of swallows from baseline to 3 months after treatment, which remained high up to 24 months after treatment. In contrast, the number of swallows of patients treated with RT or CRT (without surgery) increased from diagnosis to 3 months after treatment, after which the number of swallows returned to baseline level (Figure 2b). The cut-off score was used to develop a ROC curve indicating swallowing problems before and after treatment in patients with HNC (Appendix 1). The formula for the estimated number of swallows that were retained in the final model is shown in the footnote of Table 3. Table 2. The mean number of swallows for each timing of assessment, and the total swallowing dysfunction as indicated by the number of failed water swallowing tests and/or the number of patients above the cut-off score n: number of patients, SD: standard deviation, WST: Water swallow test *: based on number of swallows above cut-off score and/or WST failure Timing of assessment M0 M3 M6 M12 M24 n patients 115 102 99 88 72 Mean number of swallows (SD) 5.8 (2.6) 6.4 (4.2) 5.8 (3.7) 5.6 (3.4) 5.4 (4.1) n (%) n (%) n (%) n (%) n (%) Swallowing dysfunction* 22 (19.1) 22 (21.6) 19 (19.2) 13 (14.8) 10 (13.9) Number of patients above cutoff score 16 (13.9) 18 (17.6) 14 (14.1) 13 (14.8) 8 (11.1) Number of WST failures 6 (5.2) 12 (11.8) 9 (9.1) 4 (4.5) 2 (2.8) Coughing or choking 1/6 (16.7) 9/12 (75) 6/9 (66.7) 4/4 (100) 2/2 (100) Not able to drink 100 mL 5/6 (83.3) 3/12 (25) 3/9 (33.3) 0 0