For millions of people living with knee osteoarthritis, daily pain and limited movement are a reality.
Now, a new clinical trial suggests that low-dose radiation therapy could provide meaningful relief for those with mild to moderate disease, offering a safe middle ground between medications and surgery.
The randomized, placebo-controlled study, presented at the American Society for Radiation Oncology (ASTRO) Annual Meeting, found that patients who received a short course of low-dose radiation reported less pain and better physical function within four months.
The benefits came without noticeable side effects, and the treatment used only a fraction of the radiation dose typically given to cancer patients.
“Osteoarthritis patients often face a tough choice between the side effects of pain medications and the risks of joint replacement surgery,” said Dr. Byoung Hyuck Kim, the study’s lead investigator and assistant professor of radiation oncology at Seoul National University College of Medicine.
“We believe radiation could be a suitable option for those who do not respond well to drugs or injections.”
Osteoarthritis is the most common form of arthritis, affecting more than 32 million adults in the United States alone.
It occurs when the cartilage that cushions the ends of bones breaks down over time, leading to pain, stiffness, and difficulty with daily activities. Current treatments range from lifestyle changes and pain medications to joint replacement surgery for advanced cases.
Low-dose radiation has long been used in European countries like Germany and Spain as a treatment for joint pain, but its use elsewhere has been limited.
High-quality, placebo-controlled trials have been lacking, which has slowed wider acceptance. One barrier, Dr. Kim noted, is the misconception that all radiation therapy involves high doses.
“For osteoarthritis, the doses are tiny compared to cancer treatment—less than 5 percent—and they target joints away from vital organs,” he said.
In this multicenter Korean trial, 114 patients with mild to moderate knee osteoarthritis were randomly assigned to one of three groups: a low dose of radiation (3 Gy), a very low dose (0.3 Gy), or a sham group where no radiation was delivered. Each participant underwent six treatment sessions, and none knew which group they were in.
To ensure the results weren’t influenced by other medications, the use of painkillers was restricted to acetaminophen only during the study period.
After four months, 70 percent of patients in the 3 Gy group met the criteria for meaningful improvement in pain, function, or overall condition, compared to 42 percent in the placebo group.
Those in the very low-dose group did not show significant differences from the placebo arm.
Patients in the effective 3 Gy group also reported notable improvements in composite scores for pain, stiffness, and mobility, with more than half achieving better outcomes compared to less than a third of those in the placebo group.
No radiation-related side effects were observed. The researchers believe this makes the treatment particularly appealing for patients with inflammation and preserved joint structure, since it may help delay the need for joint replacement.
However, they caution that radiation cannot reverse severe osteoarthritis where cartilage is already gone.
Dr. Kim emphasized the importance of combining radiation with other standard treatments, such as physiotherapy, weight management, and exercise. “In real-world practice, we expect responses to be even stronger when radiation is used alongside other therapies,” he said.
The team is continuing to monitor patients for 12 months to see how long the benefits last and whether improvements correlate with imaging of the joints. Larger trials are also planned, including studies that will compare low-dose radiation with injections and evaluate its cost-effectiveness.
Although about 40 percent of patients in the placebo group also reported improvements—a response rate typical for osteoarthritis studies—the trial’s design allowed researchers to confirm that the radiation itself drove the better results.
“This was surprising, but it highlights the importance of placebo-controlled trials in osteoarthritis research,” Dr. Kim said.
For now, the findings suggest that low-dose radiation may be a safe and effective option for patients struggling with knee osteoarthritis, filling a gap between conservative care and invasive surgery.
