In a clinical trial, six sessions of low-dose radiation significantly eased knee osteoarthritis pain and improved function for months afterwards, hinting at a safe, drug-free alternative for millions living with joint degeneration.
For those with advanced osteoarthritis (OA) of the knee and the severe pain, swelling, and greatly reduced function that go along with it, the endpoint is often knee replacement surgery. So, alternative approaches that reduce pain, improve function, and delay surgery are welcomed.
The results of a new clinical trial led by the Seoul National University College of Medicine, and presented at this year’s American Society for Radiation Oncology (ASTRO) Annual Meeting, have shown how a single course of low-dose radiation can relieve pain and improve function in people with mild-to-moderate knee OA.
“People with painful knee osteoarthritis often face a difficult choice between the risks of side effects from pain medications and the risks of joint replacement surgery,” said Byoung Hyuck Kim, MD, PhD, the trial’s principal investigator and an assistant professor of radiation oncology at the Seoul Metropolitan Government-Seoul National University (SMG-SNU) Boramae Medical Center. “There’s a clinical need for moderate interventions between weak pain medications and aggressive surgery, and we think radiation may be a suitable option for those patients, especially when drugs and injections are poorly tolerated.”
The trial included 114 people with primary knee OA, diagnosed by moderate damage visible on X-rays, and significant pain with walking. They were randomly assigned to one of three groups: very low-dose radiation (0.3 Gy total, spread over six sessions of 0.05 Gy), low-dose radiation (3 Gy total, spread over six sessions of 0.5 Gy), or a sham treatment that did not deliver radiation.
By way of comparison, a single, routine chest X-ray delivers a dose of radiation of around 0.1 milligray (mGy), while a chest CT scan delivers around 6 to 7 mGy. Each treatment in this trial was 500 mGy, which works out to be 5,000 times the radiation dose of a chest X-ray and around 70 times the dose of a chest CT scan. However, while this sounds like a lot, the treatment delivered in the study is still considered to be low-dose. For radiotherapy cancer treatment, for example, total doses are usually 50 to 70 Gy – so a total of 3 Gy is roughly one-twentieth or less of that.
“There is a misconception that medicinal, or therapeutic, radiation is always delivered in high doses,” Kim said. “But for osteoarthritis, the doses are only a small fraction of what we use for cancer, and the treatment targets joints that are positioned away from vital organs, which lowers the likelihood of side effects.”
Trial participants couldn’t take regular pain meds during the first four months, other than occasional “rescue” meds if needed. No second round of radiation was allowed. The main treatment outcome was how many participants showed significant improvement after four months, as measured by assessments of pain and function.
The 3 Gy group did significantly better than the sham group. About 70% improved vs 42% in the sham group. Over half (57%) of people in the 3 Gy group had a clinically meaningful improvement in joint pain and function scores vs about 31% in the sham group. The 0.3 Gy group didn’t show a statistically significant improvement; about 58% improved. No meaningful differences were seen in blood markers of inflammation or in the amount of pain medication people used. The treatment was deemed to be safe, with no side effects or toxicity reported.
“The sham-controlled design helped rule out placebo effects, and we limited stronger analgesics, which made differences between groups more clearly attributable to the radiation itself,” said Kim. “In previous studies, drugs such as NSAIDs [non-steroidal anti-inflammatory drugs] or opioids were also used during the intervention or follow-up period. But using these pain relievers could mask the effects of radiation therapy.”
The findings suggest that a course of low-dose radiation can safely and significantly reduce pain and improve function in people with mild-to-moderate knee OA. But the researchers caution that the treatment may not be as effective for people with severe OA.
“For severe osteoarthritis, where the joint is physically destroyed and cartilage is already gone, radiation will not regenerate tissue,” Kim said. “But for people with mild to moderate disease, this approach could delay the need for joint replacement. In clinical practice, responses could be even stronger when radiation is properly combined with other treatments, and patient satisfaction may be higher than with current options alone.”
The researchers are conducting a 12-month follow-up assessment on study participants to assess the longevity of benefits and to correlate symptom relief with image-based measures of joint structure. They also plan to conduct larger trials to evaluate the effectiveness of the treatment in specific population groups, and compare low-dose radiation with injections and medication regimens.
The study’s abstract is available on the ASTRO Annual Meeting 2025 website.
Source: ASTRO
