Low-Dose Radiotherapy for Knee Osteoarthritis and the Growing Evidence Behind It

Decades of Experience in Germany

Low-dose radiotherapy for osteoarthritis is sometimes described as a new treatment, but there is a long history of its use in Germany and other parts of central Europe. German radiation oncologists have treated benign and degenerative conditions according to national consensus guidelines since the 1990s, and LDRT has become an established option for selected patients with painful osteoarthritis and other musculoskeletal conditions.

The scale of this experience is substantial. Historically, around 50,000 patients each year in Germany have received radiotherapy for non-cancerous conditions. In a large German patterns-of-care update, participating radiotherapy centres reported treating more than 36,000 patients with benign conditions in a single year, including almost 15,000 patients with osteoarthritis.

Knee osteoarthritis has been one of the most extensively treated indications. Across large German observational studies, around 60–80% of patients have typically reported improvement in pain, although response rates vary depending on how improvement was defined and when it was measured. A DEGRO evidence review covering more than 10,000 patients with painful knee osteoarthritis found marked or complete pain reduction ranging from approximately 58% to 91% across individual studies.

This extensive clinical experience is one reason LDRT became incorporated into German practice. However, most of these studies were observational rather than placebo-controlled. They showed a consistent signal that many patients improved after treatment, but could not reliably determine how much of that improvement resulted directly from radiation rather than patient selection, placebo effects or the natural fluctuation of osteoarthritis symptoms.

When Randomised Trials Challenged the German Experience

The first major challenge came from a Dutch double-blind, sham-controlled randomised trial involving 55 patients with persistent painful knee osteoarthritis. Patients received either six treatments of 1 Gy, for a total of 6 Gy, or six sham treatments. At three months, response rates were essentially identical: 44% after radiotherapy and 43% after sham, with no significant differences in pain, function or inflammatory measures. Longer follow-up also failed to demonstrate a delayed benefit.

This remains an important negative trial and should form part of any balanced assessment of LDRT. However, subsequent German authors have questioned whether its treatment schedule and patient population were representative of those considered most likely to respond. The trial used 1 Gy fractions rather than the 0.5 Gy schedule commonly used in Germany, and included a substantial number of patients with long-standing and more established osteoarthritis. An anti-inflammatory treatment may be less likely to produce a meaningful response once structural disease has become more advanced. These criticisms do not invalidate the Dutch findings, but they provided good reasons to test the treatment again using different patient selection and dose schedules.

The German ArthroRad trial subsequently compared the established 3 Gy regimen with an extremely low 0.3 Gy dose. In Germany, where LDRT was already established clinical practice, investigators used the ultra-low dose as a near-placebo comparator rather than a true no-radiation arm. Across the knee and hand osteoarthritis patients studied, 59% improved at three months in both groups; at 12 months, 61% had improved after 3 Gy compared with 65% after 0.3 Gy, with no significant difference between the two doses. The result was therefore encouraging in terms of overall response but could not establish how much benefit was caused by radiation, particularly because it remained uncertain whether 0.3 Gy was biologically inactive.

Newer Randomised Trials Are Strengthening the Evidence

More recent studies have begun to provide clearer answers.

A 2025 Iranian randomised study evaluated older patients with knee osteoarthritis receiving 3 Gy over six sessions. The radiotherapy group experienced improvements in pain, knee function, physical performance and analgesic use over six months, without treatment-related adverse effects. Although relatively small, the study added prospective evidence supporting the treatment schedule now commonly used for osteoarthritis.

The most important recent evidence has come from the LoRD-KNeA trial, a multicentre randomised sham-controlled study involving 114 patients with Kellgren-Lawrence grade 2 or 3 knee osteoarthritis. Patients received sham treatment, an extremely low dose of 0.3 Gy, or the established 3 Gy regimen delivered over six treatments.

At four months, 70.3% of patients receiving 3 Gy met internationally recognised OMERACT-OARSI response criteria compared with 41.7% after sham treatment. Clinically meaningful improvement in the combined WOMAC measure of pain, stiffness and physical function occurred in 56.8% compared with 30.6%, respectively.

Importantly, the 0.3 Gy group was not significantly better than sham. This is particularly interesting in light of ArthroRad, because it suggests that an ultra-low radiation dose does not provide the same treatment effect as the established 3 Gy regimen when tested against a true sham control.

LoRD-KNeA does not erase the negative Dutch data. Instead, the contrast between the trials reinforces how important radiation dose, patient selection and trial design may be when evaluating LDRT.

What Do We Know About Longer-Term Outcomes?

Another important source of evidence comes from a Russian randomised study of 292 patients with early knee osteoarthritis. Patients received standard medical treatment either alone or combined with low-dose radiotherapy and have now been followed for more than a decade.

Published results to date suggest that the potential benefit may extend beyond short-term pain relief. Disability related to knee osteoarthritis developed in 9.5% of patients who received radiotherapy compared with 17.8% in the control group, while longer-term imaging analyses have also suggested less structural progression among patients who received radiation.

There are important limitations. The study was not sham-controlled, the radiation schedule differed from the regimen commonly used today, and the population generally had relatively early disease. Nevertheless, this cohort is particularly valuable because most osteoarthritis trials examine outcomes over months rather than many years.

The next chapter from this same randomised cohort is now imminent. At the 2026 ASTRO Annual Meeting, Dr Bobby Koneru is scheduled to present approximately 13-year follow-up, examining patient-reported outcomes, structural progression and longer-term clinical endpoints.

This creates an unusually interesting progression in the evidence. We already have published long-term results suggesting differences in disability and structural progression. The upcoming analysis should tell us whether those findings remain apparent more than a decade after treatment and whether LDRT may have implications beyond short-term symptom relief.

Our Approach to Knee Osteoarthritis

At Pinpoint Radiotherapy, low-dose radiotherapy is considered for selected patients whose knee osteoarthritis continues to cause significant pain, stiffness or restriction despite appropriate conservative management.

The emerging evidence appears particularly relevant to patients with mild to moderate osteoarthritis, where inflammation may remain an important contributor to symptoms and the joint has not reached end-stage structural destruction. Assessment therefore considers the pattern of pain, imaging findings, severity of osteoarthritis, previous treatments, age and other possible causes of knee symptoms rather than simply treating an abnormal X-ray.

For suitable patients, treatment involves six short, non-invasive radiotherapy sessions, with improvement often developing gradually over the following weeks and months. LDRT does not regenerate cartilage or reverse established structural damage, and not every patient will respond. Its aim is to reduce pain and inflammation sufficiently to improve mobility and everyday function.

The evidence for knee LDRT has evolved substantially. Decades of German guideline-supported clinical experience established a consistent signal of benefit, the Dutch trial raised an important and legitimate challenge, ArthroRad left the placebo question unresolved, and a newer generation of randomised trials is now beginning to provide clearer answers. With further long-term results expected shortly, knee osteoarthritis has become one of the most actively developing areas of functional radiotherapy.