A recent randomized, placebo-controlled clinical trial has revealed that a single course of low-dose radiation therapy may serve as a safe and effective alternative treatment option for individuals suffering from painful knee osteoarthritis. The study demonstrated significant reductions in pain and improvements in physical function among patients with mild to moderate knee osteoarthritis within four months of receiving this innovative therapy, which utilizes a fraction of the radiation typically associated with cancer treatments.
The findings from the Korean trial will be presented at the American Society for Radiation Oncology (ASTRO) Annual Meeting. According to Dr. Byoung Hyuck Kim, MD, Ph.D., the principal investigator and an assistant professor of radiation oncology at Seoul National University College of Medicine, Boramae Medical Center, individuals with painful knee osteoarthritis frequently face challenging decisions regarding the side effects associated with pain medications versus the risks of joint replacement surgery. "There’s a clinical need for moderate interventions between weak pain medications and aggressive surgery," Dr. Kim noted, emphasizing that radiation therapy could be a viable option for patients who poorly tolerate drugs and injections.
Osteoarthritis is the most prevalent form of arthritis, affecting an estimated 32.5 million adults in the U.S. It occurs when the cartilage cushioning the ends of bones deteriorates over time, leading to symptoms that often manifest in the knees and hips. These symptoms can significantly restrict daily activities and diminish the quality of life. Initial treatment strategies generally focus on pain medications and lifestyle adjustments, with surgical options considered only when symptoms worsen.
In some European countries, like Germany and Spain, low-dose radiation is routinely employed for managing joint pain and is widely accepted. However, Dr. Kim pointed out that high-quality, randomized evidence demonstrating its effectiveness against placebo has been scarce until now. "There is a misconception that medicinal or therapeutic radiation is always administered in high doses," he explained. In reality, the doses used for treating osteoarthritis are only a small fraction of those typically utilized in cancer treatments, targeting joints away from vital organs to minimize side effects.
This multicenter trial involved 114 patients with moderate-to-mild knee osteoarthritis enrolled across three academic centers in Korea. Participants were randomly assigned to receive one of two radiation regimens—a very low dose (0.3 Gy) or a low dose (3 Gy)—or to a control group that underwent simulated (sham) radiation. In the placebo group, participants experienced the same setup for radiation therapy, but the treatment machine did not deliver any radiation. To maintain the integrity of the study, the use of other pain relievers was restricted, allowing only acetaminophen as needed during the first four months.
Response to treatment was assessed using internationally recognized criteria, classifying a patient as a responder if they showed meaningful improvement in at least two of three areas: pain, physical function, and overall assessment of their condition. Patients also filled out a separate questionnaire regarding pain, stiffness, and function. Remarkably, no treatment-related side effects were reported.
After four months, 70% of patients in the 3 Gy group met the responder criteria, compared to 42% in the placebo group (p=0.014). The outcomes in the 0.3 Gy group did not exhibit significant differences from the control group (58.3% improved, p=0.157), indicating that the 3 Gy regimen produced relief that extended beyond placebo effects. Furthermore, the 3 Gy group reported meaningful improvements in composite scores for pain, stiffness, and physical function more frequently than the placebo group (56.8% versus 30.6%, p=0.024).
Dr. Kim highlighted two critical distinctions in this trial compared to previous studies. The sham-controlled design helped eliminate placebo effects, and the restriction of stronger analgesics allowed for clearer attribution of differences between groups to the low-dose radiation therapy itself. In past studies, the concurrent use of NSAIDs or opioids could have masked the effects of radiation therapy.
Importantly, while responses in the placebo group were substantial—around 40% met the criteria for treatment response without actual radiation—they are consistent with rates reported in earlier osteoarthritis trials involving injections or medications. This underscores the essential role of placebo-controlled designs in osteoarthritis research, a point that warrants further examination in future studies.
Dr. Kim explained that radiation therapy may be particularly beneficial for patients experiencing underlying inflammation and those with preserved joint structure. However, for individuals with severe osteoarthritis where the joint is physically degraded and cartilage is absent, radiation will not regenerate tissue. For those with mild to moderate disease, this treatment approach could delay the need for joint replacement.
Dr. Kim emphasized that low-dose radiation therapy should be integrated into shared decision-making alongside standard treatments like weight loss, physiotherapy, and medications. Combining radiation with other therapies could potentially enhance patient outcomes and satisfaction compared to existing options. The research team is currently conducting a 12-month follow-up to evaluate the durability of benefits and to correlate symptom relief with imaging-based assessments of joint structure. Future studies are planned to include larger, pragmatic trials targeting specific subgroups and conducting health-economic analyses comparing low-dose radiation with conventional injections and medication regimens.
