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Data collection
Baseline characteristics collected included gender, age at start treatment, comorbidity according to the Adult Comorbidity Evaluation-27 (ACE-27) index, body mass index (BMI), tumor site, T and N classification (AJCC 7th edition, used at time of diagnosis), AJCC stage, HPV-status and treatment modality. HPV status was determined using immunohistochemistry for p16 and p53. In case immunohistochemistry did not provide a definite result, polymerase chain reaction was used. Skeletal muscle mass was assessed at baseline. This was performed by measuring the total cross-sectional muscle areas (CSMA) of the bilateral paravertebral and sternocleidomastoid muscles on a single CT slice at the level of C3 using the software tool SliceOmatic, as described previously (20, 24, 25). Routine pretreatment CT- of PET/CT scans were used for this purpose. The transformation formula of Swartz et al. was used to estimate CSMA at L3 level (24). The lumbar skeletal muscle mass (LSMI) was calculated by normalizing the CSMA for height, from here called the skeletal mass index (SMI). Lower values of the lumbar SMM indicate lower skeletal muscle mass with values below 43.2 cm2/m2 indicating sarcopenia (25).
Furthermore, swallowing, mouth opening and speech outcomes were collected from the speech-language pathologists’ records. For each domain an observer- as well as patient-rated outcome measure was collected before (t0) and six (t1) and twelve months (t2) post RT(+) as described below.
Swallowing outcomes
The primary observer-rated swallowing outcome was the functional oral intake scale (FOIS) which is a validated seven-point ordinal scale with lower scores indicating more intake problems (26). As primary patient-rated swallowing outcome, the SWAL-QOL was used. This is a validated 44-item questionnaire on dysphagia and its influence on daily life. It includes ten domains: burden*, food selection*, eating duration*, eating desire*, fear*, sleep, fatigue, communication, mental health*, social functioning*, and symptom frequency. The total SWAL- QOL score is calculated from the subscales marked with an asterisk. All scores range from 0 to 100 with higher scores indicating more dysphagia-related problems (27, 28).
Secondary swallowing outcomes included feeding tube dependence and pneumonia during the past six months.
Mouth opening outcomes
The primary observer-rated trismus outcome was the mouth opening (maximum central inter-incisal opening) measured in millimeters using the TheraBite® Jaw Range of Motion Scale (Atos Medical AB, Hörby, Sweden). When a patient was missing the central incisors, 19 mm was subtracted from the score (29). The patient-rated outcome was whether the patient experienced the mouth opening as limited.
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Functional outcomes after (C)RT for OPC
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