To test the validity of an Internet-based version of Expanded Prostate Cancer Index Composite (EPIC-26) versus the phone-based version. Most men will survive for years after treatment for localized prostate cancer (PCa) and may experience lasting treatment-related toxicities affecting health-related quality of life. The EPIC-26 is a validated instrument that measures health-related quality of life across 5 PCa-specific domains. Previously, EPIC-26 was administered via phone in a large multicenter clinical trial.

We developed an Internet-based version of EPIC-26. We recruited subjects from two prospective longitudinal study cohorts of PCa patients undergoing local therapy: PROST-QA, and PROSTQA-RP2. Subjects were randomized to either an "Internet-first" or "phone-first" group. Subjects were offered the alternate questionnaire modality 2 weeks after completing the initial modality.

181 subjects were offered enrollment; 133 agreed to participate. 65 subjects were randomized to the "Internet- first" group and 68 subjects to the "phone-first" group. Of these, 37 and 26 subjects respectively completed both questionnaire versions (response rate: 44.4%). Test-retest analysis showed significant intraclass correlations in all 5 domains of EPIC-26: urinary incontinence (r = 0.96), urinary irritation (r = 0.85), bowel function (r = 0.61), sexual function (r = 0.94), and hormonal function (r = 0.89). There was no effect of order of questionnaire administration.

This study demonstrates excellent correlation of responses between Internet-based and phone-based EPIC-26 administration. All domains demonstrated test-retest reliability between modalities, without ordering effect. This validates the use of internet-based EPIC-26 in international registries as part of the International Consortium for Health Outcomes Measurement effort, and may facilitate its use in clinical practice and quality improvement.