Low-Dose Radiation Therapy for Knee Osteoarthritis

Low-dose radiation therapy (LDRT) is an outpatient treatment that directs a very small amount of radiation at an arthritic joint, aiming to calm inflammation in the joint lining. Among the joints where LDRT is used, the knee has the most direct sham-controlled trial evidence behind it.

What the Knee-Specific Evidence Shows

A multicenter, randomized, sham-controlled trial led by investigators at Seoul National University, presented at the ASTRO 2025 Annual Meeting, enrolled 114 patients specifically with knee osteoarthritis. Patients were assigned to 3 Gy in six fractions, 0.3 Gy in six fractions, or sham treatment. At four months, 70.3% of the 3 Gy group met the study's response criteria, compared with 41.7% of the sham group (p=0.014). The 0.3 Gy group was not significantly different from sham, and no treatment-related toxicity was reported.^[1]

A separate 2019 Dutch randomized, double-blinded, sham-controlled trial also looked specifically at knee osteoarthritis and found no substantial benefit for symptoms or inflammatory signs, a reminder that the evidence for the knee, while more direct than for other joints, is still mixed rather than settled.^[6]

The ongoing US MOBILE study (Mitigating Osteoarthritis by Intervention with Low-Dose Irradiation to Extremities) is a prospective observational study, not a randomized trial, covering knees and other treated joints. Its 2025 interim analysis included 108 patients and 150 treated joint sites; among the 76 sites with six-month follow-up, mean pain score decreased from 7.6 to 3.4, and 84% of patients reported some pain improvement.^[3]

Typical Schedule

• Total dose of about 3.0 Gy, split into 6 treatments of 0.5 Gy each
• Treatments given 2 to 3 times per week, over about 2 to 3 weeks
• Each visit takes roughly 10 to 15 minutes; no needle, sedation, or recovery period

Who May Be a Candidate

Programs generally consider adults with knee osteoarthritis who have not gotten enough relief from medications, injections, physical therapy, or other conservative treatments. The strongest recent sham-controlled evidence involved patients with mild-to-moderate knee osteoarthritis; patients with more advanced structural damage may be less likely to improve, since LDRT cannot regrow cartilage or restore a severely damaged joint. Many programs are cautious about using LDRT in younger adults, since radiation-related risk has more time to develop. A radiation oncologist weighs age, joint condition, prior treatment, and overall health together.

References:
1. Kim BH, et al. Clinical Effectiveness of Single Course Low-Dose Radiation Therapy in Knee Osteoarthritis: Short-term Results from the Randomized, Sham-Controlled Trial. ASTRO 67th Annual Meeting Late-Breaking Abstract LBA 06. 2025. Abstract
3. Byrd HF, et al. Interim Analysis of Mitigating Osteoarthritis by Intervention with Low-Dose Irradiation to Extremities (MOBILE). ASTRO 2025 Annual Meeting, Abstract 249. Abstract
6. Mahler EAM, et al. Effectiveness of low-dose radiation therapy on symptoms in patients with knee osteoarthritis: a randomised, double-blinded, sham-controlled trial. 2019. PubMed