Background: The Expanded Prostate Cancer Index Composite questionnaire is widely used as a comprehensive assessment of health-related quality of life issues in prostate cancer management, distinguishing urinary, bowel, sexual, hormonal domains. The primary purpose of this study was to assess the factor structure of this questionnaire. Patients and Methods: A principal component analysis with orthogonal (varimax) rotation was conducted on data collected from 418 patients after primary (external beam radiotherapy and permanent iodine-125 brachytherapy) and postoperative radiotherapy for prostate cancer. Results: Health-related quality of life scores well demonstrated differences in subpopulations before radiotherapy and different toxicity profiles of specific radiotherapy concepts. The extraction of 12 factors accounted for 75.5% of the variance. With exception of the sexual domain, a strong dependence between the function in a domain and the related bother was found. The concept to discriminate urinary incontinence and urinary irritation/ obstruction subscales was supported. However, the items ‘bleeding with urination’ and ‘bloody stools’ have loaded on separate factors. After separation of the items of the function and bother subscales, a 4-factor solution was confirmed to be optimal, respectively. Conclusion: The obtained factor structure corresponds to the original Expanded Prostate Cancer Index Composite subscales. Minor divergences have been found, depicting especially items concerning ‘incontinence’ and ‘bleeding’ as distinct aspects of a domain.
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