Can LDRT Cause Cancer? The Radiation Risk, Explained

Yes, it is possible in theory. Radiation can damage DNA, and under the standard safety model there is no dose of radiation with zero cancer risk. The risk rises with the dose^[2]. The American Radium Society's 2026 guideline says this plainly. That is the honest starting point.

What follows is what decades of actual patient data say. The observed risk is very small. No published study has ever shown a link between LDRT for osteoarthritis and a later cancer, and the expert panel's conclusion is that the rate of secondary malignancy at these doses "is believed to be extremely low"^[2]. "Theoretical but tiny" is the fair summary. Here are the numbers behind it.

What Dose You Actually Get

The two most common regimens are 0.5 Gy or 1 Gy per session, for six sessions, a total of 3 to 6 Gy to the treated joint, given every other day or twice weekly^[2]. That is the dose the joint itself receives, and it is significantly lower than the doses used to treat cancer^[2]. The whole point of these very low doses is to calm inflammation while keeping the cancer risk as small as possible.

To compare against familiar exposures, a 6 Gy course to the knee carries an estimated whole-body effective dose of about 13 mSv, roughly what one abdominopelvic CT scan delivers^[2]. The average American receives about 3.1 mSv a year from natural background radiation (cosmic rays, radon, the ground)^[4]. So a full course is on the order of four years of natural background. Not zero, and not large. Modern treatment planning also keeps the beam tight to the joint and follows the ALARA principle: keep every dose "as low as reasonably achievable," with shielding of nearby tissue where needed (for example, gonadal shielding for hip treatments and lead shielding for hand treatments)^[2].

What Decades of Patients Show

This treatment is not new. Germany has used low-dose radiotherapy for joint and tendon conditions for decades. In 2016 alone, more than 250,000 treatment courses were given there for non-cancer conditions^[3]. That long history is what makes a long-term safety study possible.

The largest such study followed 4,699 patients treated between 1994 and 2011 (average age 64, with an expected 21 more years of life). Three solid cancers developed within previously treated areas, 0.064 percent^[3]. At 12.5 years, 99.0 percent of patients treated at sites away from bone marrow remained free of blood cancers, versus 97.7 percent for those treated near marrow-rich areas, a real but small difference of 1.3 percentage points^[3]. The authors concluded the treatment looks safe for peripheral joints like the knee, elbow, hand, and foot, and should be used with care near the trunk and pelvis, where marrow and organs overlap the field.

Smaller studies point the same way. After shoulder LDRT, 158 women were followed for a median of 21 years: 4.4 percent developed breast cancer, compared with 5.9 percent expected in the general population. No increase^[2]. And after reviewing 44 studies, the American Radium Society panel wrote that "no association of LDRT with secondary malignancy has ever been published," adding the honest caveat that incomplete follow-up does not prove the absence of a risk^[1][2].

Why Age Matters

Radiation-induced cancers need years to decades to develop, and younger cells divide faster. Both facts push the risk down in older patients, which matters because most LDRT patients are older adults. Published estimates put the lifetime risk of a fatal radiation-induced cancer from a 6 Gy knee course at 2 in 1,000 for a 25-year-old, 0.7 in 1,000 for a 50-year-old, and 0.3 in 1,000 for a 70-year-old^[2]. The risk is not zero at any age, but it shrinks steeply with it.

The Honest Caveats

• Most risk numbers are estimates extrapolated from atomic-bomb survivor data, a very different kind of exposure from a small beam aimed at one joint^[2]. Treat them as rough guides, not measurements.
• Many studies have limited long-term follow-up. "No association published" is not the same as "proven safe." The guideline says exactly that^[2].
• The theoretical risk is highest for joints near radiation-sensitive areas, the spine, pelvis, and shoulder (near breast tissue), and lowest for knees, elbows, hands, and feet^[2][3].

References:
1. Dove A, et al. American Radium Society (ARS) Appropriate Use Criteria (AUC) for Low-Dose Radiotherapy for Treatment of Osteoarthritis. American Journal of Clinical Oncology. Published online May 25, 2026, ahead of print. PubMed
2. American Radium Society Appropriate Use Criteria for Use of Radiotherapy for Treatment of Osteoarthritis. Expert Panel for Use of Radiotherapy in the Treatment of Arthritis. 2026. Full guideline document. Full document (PDF)
3. Risk of radiation-induced malignancy after low-dose radiotherapy for non-malignant musculoskeletal disorders: A long-term retrospective analysis of n=4699 patients. International Journal of Radiation Oncology, Biology, Physics. 2026. Red Journal abstract
4. Radiation in Perspective. U.S. Department of Energy, citing NCRP Report No. 160. Average American receives about 310 mrem (3.1 mSv) per year from naturally occurring sources. DOE