A new clinical study has shown that a single session of low-dose radiation therapy may provide a safe and effective option for patients with rheumatoid arthritis in the knee, especially in mild to moderate cases.

Researchers reported that patients who received this treatment noticed a significant reduction in pain and improvement in mobility over the following four months, noting that the doses used were much lower than those applied in cancer treatment. Since the study included a control group, the team was able to exclude the placebo effect, which is common in arthritis studies.

The trial involved 114 patients across three medical centers in South Korea, randomly assigned into three groups: the first received a very low dose (0.3 Gray – an international unit measuring absorbed radiation dose), the second a low dose (3 Gray), while the third underwent a sham procedure without radiation. All participants received six treatment sessions, with only paracetamol allowed for pain relief during follow-up.

After four months, 70% of patients in the 3 Gray group responded, compared to 42% in the control group, a difference described by researchers as “statistically significant.” More than half of the patients in this group showed clear improvement in pain and motor functions, with no radiation-related side effects observed.

Dr. Byung Hyuk Kim, the lead researcher from Seoul National University, said: “There is an urgent need for alternative treatments between mild painkillers and joint replacement surgery. Low-dose radiation therapy may represent this option, especially for patients who cannot tolerate medications or injections.”

Kim explained that the treatment might be more effective in patients whose joints still maintain their structure, while its benefit decreases in severe cases accompanied by advanced cartilage erosion.

The team plans to conduct longer follow-up studies up to 12 months, in addition to broader clinical trials and economic analyses comparing low-dose radiation therapy with injections and conventional drugs.

The preliminary results of the study will be presented at the annual meeting of the American Society for Radiation Oncology (ASTRO).