Bringing Trial Activities to Participants—The Trials@Home <scp>RADIAL</scp> Proof‐of‐Concept Trial Investigating Decentralization of Trials

The interest in trials in which activities are being moved to the participants' direct environment, that is, decentralized, has increased in recent years, but limited research has been conducted into the feasibility and acceptability of such approaches. The Trials@Home RADIAL proof-of-concept (PoC) trial aims to assess the scientific and operational feasibility and quality of a fully decentralized and hybrid trial approach compared to a conventional, site-based approach. RADIAL is a three-arm parallel-group, open-label, multi-center low-intervention phase IV trial conducted in people living with Type 2 diabetes mellitus in six European countries (DE, DK, ES, IT, PL, UK). The RADIAL trial compares three arms with the same clinical intervention (Insulin Glargine 300 U/mL) but differing degrees of decentralization (the methodological intervention), including online recruitment, remote consenting, remote visits, home-shipment of Investigational Medicinal Product and study materials, home-based biological sample collection, app-reported events/ePROs, and home-devices for data collection. Key Performance Indicators regarding recruitment, retention, diversity, site satisfaction, participant satisfaction, cost, safety oversight, treatment adherence, and data quality are the main outcomes of the trial. This paper discusses the set-up of RADIAL, describing the design, endpoint selection, and decentralized elements evaluated, as well as discussing insight from RADIAL for future PoC trials. This is the introductory paper in a series of six papers in which we share the lessons learned during set-up, regulatory submission, and conduct of RADIAL. By sharing these insights, we aim to support clinical trial designers, technology developers, and other stakeholders to successfully implement decentralized elements into clinical trials. This trial was registered with identifier NCT05780151 in clinicaltrials.gov and under 2022-500,449-26-00 in the Clinical Trials Information System (CTIS) clinical trial database.