Converting between the International Prostate Symptom Score (IPSS) and the Expanded Prostate Cancer Index Composite (EPIC) urinary subscales: modeling and external validation

Background: Prostate-related quality of life can be assessed with a variety of different questionnaires. The 50-item Expanded Prostate Cancer Index Composite (EPIC) and the International Prostate Symptom Score (IPSS) are two widely used options. The goal of this study was, therefore, to develop and validate a model that is able to convert between the EPIC and the IPSS to enable comparisons across different studies. 
Methods: Three hundred forty-seven consecutive patients who had previously received radiotherapy and surgery for prostate cancer at two institutions in Switzerland and Germany were contacted via mail and instructed to complete both questionnaires. The Swiss cohort was used to train and internally validate different machine learning models using fourfold cross-validation. The German cohort was used for external validation.
Results: Converting between the EPIC Urinary Irritative/Obstructive subscale and the IPSS using linear regressions resulted in mean absolute errors (MAEs) ..., , , # Converting between the International Prostate Symptom Score (IPSS) and the Expanded Prostate Cancer Index Composite (EPIC) urinary subscales: modeling and external validation

[https://doi.org/10.5061/dryad.v6wwpzh4b](https://doi.org/10.5061/dryad.v6wwpzh4b)

The study was conducted in radiation oncology departments at two institutions, the Cantonal Hospital Winterthur in Switzerland and the Ruppiner Kliniken GmbH in Germany.

Three hundred and forty-seven consecutive patients who had received radiation therapy for prostate cancer in the post-operative setting at our institutions between 2010 and 2020 were identified and received the German versions of the EPIC and IPSS questionnaires in August 2020, unless a date of death had been documented in our electronic health records. Patients completed the questionnaires based on their current quality of life and symptom burden.

We received responses from 208 patients. Of these responses, 175 had no missing values for any of the quality of l...