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.