80 flow rate was expressed in milliliters per 10 minutes (ml/10 min) for both parotid glands and the submandibular gland. In the present study, we used the total amount of saliva by adding up the saliva of both parotid glands and the submandibular gland. No oral stimulus was permitted for at least 30 minutes before saliva collection, including the WST and MAT.27 In previous research, this test scored an ICC of 0.66 and 0.63 for the left and right parotid flow glands, indicating moderate test-retest reliability.28 EORTC QLQ-H&N35 The EORTC QLQ-H&N35 is an additional questionnaire to the EORTC QLQ-C30 (core instrument), and widely used to measure QoL in patients with HNC.20 It consists of 7 subscales: pain in the mouth (4 items), problems with swallowing (4 items), senses (2 items), speech (3 items), social eating (4 items), social contact (5 items), sexuality (2 items), and eleven single items which address problems with teeth, opening mouth, dry mouth, sticky saliva, coughing, feeling ill, painkillers, nutritional supplements, feeding tube, weight loss, and weight gain.29 The scores are transformed to a scale of 0 to 100, with a higher score on the symptom scales implying a higher level of symptoms or problems.20 In the present study, we used the subscales ‘pain in mouth’ and ‘social eating’, and the single items ‘teeth’, ‘opening mouth’, ‘weight loss’, and ‘weight gain’ to explore the association between these PROs and the MAT. The subscales ‘pain in mouth’ and ‘problems with swallowing’, and the single items ‘dry mouth’, ‘coughing’, and ‘feeding tube’ were used to explore the association between these PROs and the WST. The single items ‘dry mouth’ and ‘sticky saliva’ were used to explore the association between these PROs and the salivary output. This questionnaire performs well on internal consistency and construct validity, and is able to differentiate between diverse groups of patients regarding treatment, tumor size, time elapsed since treatment, and age.30 In patients with HNC, Cronbach’s α range from 0.75 to 0.93 for most scales, indicating satisfactory internal consistency.20,31 SWAL-QOL The SWAL-QOL consists of 39 items on 8 subscales: general burden, food selection, eating duration, eating desire, fear of eating, mental health, social functioning, and symptoms.21,29 After completing, a total SWAL-QOL score could be calculated based on 23 items (item 1-9 and 12-25). The scores range from 0 to 100, with a higher score indicating more impairment.29 In the present study we used the subscales ‘food selection’, ‘eating duration’, ‘eating desire’, ‘fear of eating’, and the total score to explore the association between these PROs and the MAT. We used the subscales ‘general burden’, ‘symptoms’, and the total score to explore the association between these PROs and the WST. Cronbach’s α ranges from 0.79 to 0.95 in patients with oropharyngeal dysphagia, and intraclass correlations range from 0.59 to 0.91, indicating excellent scale reliability.32
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