Abstract / Summary
Low-dose radiotherapy (LDRT) has been used as a non-pharmacological treatment for osteoarthritis (OA), but robust evidence from randomized, sham-controlled trials remains limited. We evaluated the clinical effectiveness and temporal response of two single-course LDRT regimens compared with sham irradiation in patients with knee OA. In this multicenter, randomized, sham-controlled trial, 114 patients with knee OA were allocated to receive sham irradiation, a total of 0.3 Gy in 6 fractions, or a total of 3 Gy in 6 fractions. Key inclusion criteria were primary knee OA, age ≥ 50 years, and a baseline walking pain score of 50–90/100. The primary endpoint was the OMERACT–OARSI responder rate at 4 months. In the modified intention-to-treat analysis, the 4-month responder rate was significantly higher in the 3 Gy group (70.3%) than in the sham group (41.7%; p = 0.021), whereas the 0.3 Gy group did not differ significantly from sham (58.3%; p = 0.168). The superior responder rate in the 3 Gy group persisted at 8 months but was no longer statistically significant at 12 months. Similar findings were observed in the per-protocol analysis. Mean changes in secondary outcomes, including WOMAC subscales, VAS, PGA, inflammatory markers, and MRI-based parameters, did not differ significantly among groups. No treatment-related toxicities were reported. A single course of 3 Gy LDRT resulted in a significant short-term improvement in the responder rate in patients with knee OA, although no distinct benefits were observed in secondary continuous clinical or imaging outcomes. The findings highlight a time-limited treatment effect beyond an early placebo response and require further investigation of LDRT as a conservative, non-pharmacological option for selected patients. Trial registration: clinicaltrials.gov NCT05562271.