Most people associate radiation therapy with cancer treatment. But for decades, a very different application of the same technology — low-dose radiotherapy (LDRT) — has been used in Europe to relieve joint pain from osteoarthritis (OA). It’s now drawing renewed interest worldwide, including in the United States. Here’s what patients and clinicians should know.
The Scale of the Problem
Osteoarthritis affects an estimated 595 million people globally, making it a leading cause of pain and disability across all regions. Projections suggest the burden will keep growing: by 2050, knee OA cases are expected to rise nearly 75%, hip OA by almost 79%, and hand OA by close to 49% compared to 2020.
Conventional Treatment & Why Radiation?
Conventional treatment — physical therapy, NSAIDs, injections, and eventually joint replacement — helps many patients. But a significant proportion, particularly elderly individuals or those unfit for surgery, remain symptomatic despite these options.
Although OA was traditionally viewed as pure mechanical wear-and-tear, it’s now understood to also involve active proinflammatory processes. This provides a rationale for exploring an anti-inflammatory therapy like LDRT.
At doses used for OA, radiation appears to work through immune and vascular modulation rather than tissue destruction.
Key mechanisms include:
- Calming inflammatory cells and signals
- Modulating immune-cell behavior
- Affecting endothelial cells and macrophages
- Supporting new bone-matrix formation while reducing bone degradation
- Altering cytokine, adhesion-molecule, nitric-oxide, and oxidative-burst activity
Clinical Evidence
The evidence is promising but not yet definitive.
Typical treatment uses 3–6 Gy total, delivered in small fractions of 0.5–1.0 Gy over 2–3 weeks. Emerging evidence suggests that 0.5 Gy per fraction (3 Gy total) may produce a stronger anti-inflammatory response than the older 1 Gy-per-fraction, 6 Gy protocol.
Retrospective studies report meaningful pain relief in approximately 58–91% of knee OA patients.
Randomized trials have been mixed. Some found no benefit over sham treatment, although these studies have been criticized for small sample sizes, short follow-up, and protocol differences. More recent trials have been more encouraging, including a 2025 randomized placebo-controlled trial showing significant improvements in pain and physical function over four months in patients with mild-to-moderate knee OA.
About 40% of patients may require a second course of radiotherapy at 6–12 weeks to see benefit.
Safety
The radiation doses used for OA are only a small fraction of those typically used for cancer treatment. Reviews cited in the article suggest that the absolute cancer risk may be negligible in elderly populations, who make up the typical OA patient demographic.
However, important questions remain regarding long-term carcinogenic risk, as treatment protocols, doses, and patient populations vary.
Where Things Stand Today
LDRT for OA has a long history of use outside the United States and is experiencing renewed interest because of improved understanding of its mechanisms and the growing need for alternatives in an aging population.
Ongoing studies, including the IMMO-LDRT01 trial in Germany, are examining immune-system changes associated with treatment. The article emphasizes that well-designed prospective randomized trials are still needed to establish definitive effectiveness.
Bottom Line
LDRT is presented as a legitimate, actively researched option, typically for older adults with painful OA that has not responded adequately to standard conservative treatment. The biological rationale is increasingly well understood and newer randomized trials are encouraging.
However, it is not first-line therapy, dosing protocols are still being refined, and patients should have an informed discussion with their care team about the current evidence before considering it.