The Groningen Radiotherapy-Induced Xerostomia questionnaire: development and validation of a new questionnaire.

Abstract

The purpose of this study was to develop and validate a questionnaire (Groningen Radiotherapy-Induced Xerostomia (GRIX) questionnaire) that has the ability to distinguish between patient-rated xerostomia during day and night and can be used to evaluate the impact of emerging radiation delivery techniques aiming at prevention of xerostomia in more detail. All questions in the GRIX were generated from an exhaustive list of relevant questions according to xerostomia as reported in the literature and reported by patients and health care providers. Finally the GRIX was reduced from 56 questions to a 14-item questionnaire, with four subscales; xerostomia during day and night and sticky saliva during day and night. 315 patients filled out 2936 questionnaires and the GRIX was evaluated by calculating Crohnbach's α for all subscales. Criterion validity was evaluated to compare the GRIX with patient-rated xerostomia scored with the EORTC QLQ-HN35 and physician-rated xerostomia, test-retest analysis and responsiveness were also tested. Crohnbach's α varied for all subscales between 0.88 and 0.94. The GRIX scored well for criterion-related validity on all subscales with high correlations with the EORTC QLQ-HN35 xerostomia and sticky saliva scale as well with physician-rated toxicity scoring. No significant differences were found between test and retest score and the GRIX showed good responsiveness with different time points for all subscales. The GRIX is a validated questionnaire which can be used in future research focusing on patient-rated xerostomia and sticky saliva during day and night in relation with the impact of emerging radiation delivery techniques aiming at reduction of xerostomia.