Is LDRT Safe? Understanding the Radiation Dose in Plain English

A course of low-dose radiation therapy for osteoarthritis delivers 3 to 6 Gy in total to the treated joint, in visits of 0.5 to 1 Gy, usually two to three visits a week. A common course in the United States is 3 Gy in six visits. By comparison, a course of radiation for breast or head and neck cancer is typically 45 to 70 Gy.

The Dose Itself

The German DEGRO guideline, a reference many programs work from, recommends single doses of 0.5 to 1.0 Gy and total doses of 3.0 to 6.0 Gy per series, applied with two to three fractions per week^[1]. A fraction is simply one visit's share of the total. Nothing about the course is given all at once.

United States practice looks much the same. In a 2025 series from a single institution, 69 patients and 168 joints, each phase of treatment was 3 Gy in six fractions of 0.5 Gy, delivered over two to three weeks, and 33 percent of joints later received a second phase^[2].

What is a gray? The National Cancer Institute defines it as a measure of the amount of radiation energy absorbed by one kilogram of human tissue^[3]. In LDRT, that tissue is one joint and the tissue immediately around it: the cartilage, the joint lining, the neighboring bone, and the muscles and connective tissue nearby. The dose is measured where it lands. It is not a dose to your whole body, and that distinction drives everything else on this page.

Why the Dose Is Not Smaller, and Not Larger

Patients sometimes ask why the dose cannot simply be turned down further, to be extra safe. A blinded trial has now tested exactly that. In the Korean LoRD-KNeA trial, 114 people with knee osteoarthritis received sham treatment, a total of 0.3 Gy in six sessions, or a total of 3 Gy in six sessions, and neither the patients nor the assessors knew which. At four months, 70.3 percent of the 3 Gy group met the trial's responder standard, compared with 41.7 percent of the sham group. The 0.3 Gy group, at 58.3 percent, did not separate significantly from sham^[4].

So a tenth of the standard dose did not beat a pretend treatment. The dose used in practice sits where it does for a reason. The same trial also shows the limit of that claim: the advantage of the 3 Gy group was still present at eight months and was no longer statistically significant at twelve months, the trial's other measures of pain, stiffness, and function did not differ significantly between groups, and no treatment-related toxicities were reported^[4].

And why not larger? Because the aim is different. At cancer doses, the goal is to kill cells. At 3 to 6 Gy, the goal is to calm inflammation in a joint. There is no benefit case for pushing an arthritis dose up toward cancer levels, and no program does.

The Comparison That Is Fair

Cancer radiotherapy is prescribed in the same unit, Gy to tissue, so this comparison is like for like. A course of radiation for breast cancer or a head and neck cancer typically runs from 45 to 70 Gy^[5][6]. Set 3 to 6 Gy next to that and you get roughly 7 to 23 times less.

What does the difference mean for the tissue around your joint? Dose is what drives both the effect and the risk. A dose chosen to destroy a tumor is hard on everything in its path, which is why cancer treatment plans work so hard to shape and limit the field. A dose in single digits, aimed at one joint, is a different order of exposure for the tissue nearby. It is low, but low is not zero, which is why the last section of this page exists.

Why You Cannot Compare This to a CT Scan

Search for radiation doses online and you will find numbers like these. A CT scan of the abdomen and pelvis is about 7.7 mSv. A CT scan of the chest is about 6.1 mSv. A chest X-ray is about 0.1 mSv, and an X-ray of a hand or foot is under 0.001 mSv^[7]. Natural background radiation adds up to about 3.1 mSv a year for the average person in the United States, out of 6.2 mSv a year from all sources combined^[8][9].

Those numbers are real. They are also a different measurement. They are effective dose, in millisieverts, or mSv. RadiologyInfo.org, the patient site of the Radiological Society of North America and the American College of Radiology, defines effective dose as a calculated value that takes into account the absorbed dose to all the organs of the body, the relative harm level of the radiation, and the sensitivity of each organ. It relates to the overall long-term risk to an average person, it is useful for comparing one imaging procedure with another, and it is not intended to apply to a specific patient^[10].

Your LDRT dose is absorbed dose, in Gy, to one joint. Effective dose is a whole-body risk calculation for an average person. Turning one into the other would take a full organ-by-organ calculation for your own treatment plan, and a simple comparison to a CT scan skips all of that. So if a website or a forum post tells you that a course of LDRT equals a set number of CT scans, or a set number of years of background radiation, it has compared two different things as if they were the same. The background and imaging figures still tell you something useful: radiation is part of ordinary life and of ordinary medical care, and the amounts involved in diagnosis are small. They just are not a yardstick for your treatment.

What Happens to the Radiation Afterwards

Nothing stays behind. LDRT is external beam treatment: a machine makes the beam, the beam is present only while the machine is operating, and no radioactive material is placed in your body. Memorial Sloan Kettering puts it directly: external-beam therapy does not make a person radioactive in any way, and a person who has had it cannot contaminate or transfer radiation to anyone else^[11]. The International Atomic Energy Agency says the same in its patient guide: external beam radiotherapy does not make patients radioactive^[12].

So there is nothing to pass to a partner, a child, or a grandchild. You do not need to sleep apart, keep a distance, or avoid holding anyone after a session. The treatments people sometimes picture, where a radioactive source or a radioactive liquid is put inside the body, are different treatments. LDRT is not one of them.

Low Is Not Zero

A low dose is not a zero dose, and this page will not pretend otherwise. Any radiation exposure carries a theoretical long-term risk, and weighing that risk is part of deciding whether the treatment is worth it for you. The American Radium Society panel that reviewed the evidence for osteoarthritis, 52 studies in all (44 selected from 548 articles, plus 8 found through citation searches), reported overall response rates of 60 to 90 percent across the studies it reviewed, and also said that further high-quality studies are warranted^[13]. That range covers different joints and different definitions of a response, so it is not a promise for any one patient.

The long-term risk question deserves more room than this page can give it, and it has it. Our page on whether LDRT can cause cancer works through the doses, the decades of follow-up data from patients treated in Europe, and the estimates, in detail. What this page can leave you with is the scale: the dose is measured in single digits, it is aimed at one joint, and it is given in small amounts over several visits. That is what "low-dose" means when a radiation oncologist says it.

References:
1. Ott OJ, Niewald M, Weitmann HD, et al; German Cooperative Group on Radiotherapy for Benign Diseases (GCG-BD). DEGRO guidelines for the radiotherapy of non-malignant disorders. Part II: Painful degenerative skeletal disorders. Strahlentherapie und Onkologie. 2015;191(1):1-6 (single fraction doses of 0.5 to 1.0 Gy and total doses of 3.0 to 6.0 Gy per series, applied with 2 to 3 fractions per week). PubMed
2. Koneru BN, Sick J, Shaikh HA, Spengler H, Small W Jr, Shaffer R. Low-dose radiation therapy for osteoarthritis: a retrospective single-institution analysis of 69 patients and 168 joints. International Journal of Radiation Oncology, Biology, Physics. 2025;123(2):352-360 (each phase 3 Gy in 6 fractions of 0.5 Gy over 2 to 3 weeks; 33% of joints received a second phase). PubMed
3. National Cancer Institute. Radiation Therapy for Cancer. Patient fact sheet (a gray is a measure of the amount of radiation energy absorbed by 1 kilogram of human tissue). cancer.gov
4. Kim BH, Ro DH, Wang JH, et al. Single course low-dose radiation therapy in knee osteoarthritis (LoRD-KNeA): a randomized controlled trial. BMC Medicine. 2026 (114 patients; responders at 4 months 70.3% at 3 Gy vs 41.7% sham, p = 0.021; 0.3 Gy group 58.3%, p = 0.168, not significantly different from sham; advantage present at 8 months, not significant at 12 months; secondary outcomes did not differ significantly; no treatment-related toxicities). BMC Medicine
5. Reuters Health Rounds, reporting the ASTRO 2025 annual meeting, September 30 and October 1, 2025 (postoperative radiation doses after surgery for breast and head and neck cancers typically range from 45 to 60 Gy). Reuters
6. Cancer Care Ontario. Dose Objectives for Head and Neck IMRT Treatment Planning. Recommendation report (planning targets for a high-dose volume of 70 Gy in 35 fractions). Cancer Care Ontario
7. RadiologyInfo.org (Radiological Society of North America and American College of Radiology). Radiation Dose from X-Ray and CT Exams. Reviewed April 15, 2025 (approximate effective doses: CT abdomen and pelvis 7.7 mSv; CT chest 6.1 mSv; chest X-ray 0.1 mSv; extremity X-ray less than 0.001 mSv). RadiologyInfo.org
8. United States Environmental Protection Agency. Radiation Sources and Doses. (average annual radiation dose per person in the United States is 6.2 mSv, citing NCRP Report No. 160). EPA
9. National Council on Radiation Protection and Measurements. NCRP Report No. 160: Ionizing Radiation Exposure of the Population of the United States. 2009 (ubiquitous background 3.11 mSv per person per year; medical 3.00 mSv; total 6.2 mSv). NCRP
10. RadiologyInfo.org. What is radiation dose? Reviewed June 7, 2024 (effective dose is a calculated value in mSv, accounting for all organs, relative harm, and organ sensitivity; it relates to overall long-term risk for an average person and is not intended to apply to a specific patient). RadiologyInfo.org
11. Memorial Sloan Kettering Cancer Center. Answers to Common Questions about Radiation Safety. (external-beam therapy does not make a person radioactive; the radiation is present only when the linear accelerator is operating; no contamination or transfer to another person). MSK
12. International Atomic Energy Agency. Radiotherapy: what patients need to know. (external beam radiotherapy does not make patients radioactive). IAEA 13. Dove A, Koneru B, Small W Jr, et al. American Radium Society (ARS) Appropriate Use Criteria (AUC) for Low-Dose Radiotherapy for Treatment of Osteoarthritis. American Journal of Clinical Oncology. 2026 (548 articles identified, 44 included, 8 more from citation searches; overall treatment response rate of 60% to 90%; further high-quality studies warranted). PubMed