KORT – Knee osteoarthrosis radiotherapy trial: Protocol for a multidisciplinary pathway and a planned sham-controlled phase III trial of low-dose radiotherapy in knee osteoarthritis

Objective: Low-dose radiotherapy (LDRT) is widely used in German-speaking countries for painful degenerative and inflammatory musculoskeletal disorders, but recent sham-controlled trials using non-standard dose concepts reported no superiority over placebo. Methodologically robust trials using established LDRT regimens and guideline-based conservative care are needed. KORT aims to evaluate feasibility and inform a definitive sham-controlled efficacy trial of LDRT in knee osteoarthritis (OA). Materials and methods: KORT is a two-stage research program at University Hospital Halle (Saale). Stage 1 is a prospective, non-randomized Phase II external pilot comparing (i) standard LDRT alone versus (ii) structured orthopaedic assessment with optimization of guideline-based conservative therapy prior to LDRT. Key feasibility outcomes include recruitment, adherence, data completeness, and follow-up rates. Clinical outcomes include OARSI-OMERACT responder status at 3 months, WOMAC, SF-36, and movement pain (NRS), assessed at baseline, end of treatment, and 3 months; follow-up at 12 and 24 months is planned. Stage 2 is a planned multicenter Phase III randomized, single-blind, sham-controlled superiority trial in which all participants will undergo standardized orthopaedic optimization prior to randomization to LDRT (6 × 0.5 Gy) or sham irradiation. Results: This protocol specifies eligibility criteria, interventions, outcomes, data management, and the statistical framework. Phase II will provide empirically grounded estimates for workflow refinement and Phase III sample size assumptions. Conclusions: KORT integrates radiation oncology and orthopedics within a structured multidisciplinary framework and will enable a clinically relevant, adequately powered sham-controlled trial to determine the incremental therapeutic effect of LDRT in knee OA.