It is one of the first things people ask after hearing the word "radioactive": will I be a danger to my partner, my grandchildren or my pets? The honest answer is that it depends almost entirely on one question — does a radioactive source stay inside your body after treatment, or not?
With most brachytherapy (all high-dose-rate treatment and every temporary implant), the source is taken out before you leave the treatment room. The US National Cancer Institute (NCI) states that "there is no radiation in your body after the catheter or applicator is removed", and that it is then "safe for people to be near you–even young children and pregnant women".
Only permanent seed implants — used mainly for prostate cancer — leave a low, steadily fading source in the body. That is the situation where centres give written precautions, mostly about pregnant people and young children, for a limited period. This guide explains each situation, shows how real hospital instructions differ, and explains the rules behind them. It is general information: your own centre's written instructions always come first.
Short answer: it depends on permanent vs temporary sources
Brachytherapy places a sealed radioactive source inside or next to a tumour. What matters for the people around you is where that source is after you go home:
- Source removed (HDR, temporary low-dose-rate or pulsed-dose-rate implants): nothing radioactive remains in you, so there is nothing to protect others from. Macmillan Cancer Support puts it simply: "As soon as the source is removed from your body, there is no risk to people around you. You are not radioactive."
- Source left in place (permanent seeds): the seeds give off low-energy radiation that is mostly absorbed by the surrounding tissue. Macmillan notes that "it is safe for you to be around most people", but "you may have to avoid close contact with children or people who are pregnant for a time."
If you are not sure which type you are having, our guide to permanent (LDR) vs temporary (HDR) brachytherapy explains the difference.
After HDR or temporary implants: no source stays in the body
In high-dose-rate (HDR) brachytherapy, a machine called an afterloader sends a single source into an applicator or thin tubes for minutes, then pulls it back into a shielded safe. The NCI describes the source being "left in place for just 10 to 20 minutes at a time and then taken out". Temporary low-dose-rate implants stay in longer — the NCI says "1 to 7 days" — but are also removed before you go home.
Once the source is out, you can hug, sleep next to, cook for and look after anyone, including babies and pregnant people. This applies, for example, to vaginal cuff brachytherapy, where no source stays in the body, to HDR for cervical cancer, and to HDR prostate treatment. Macmillan's prostate page states that after HDR no precautions are needed, because no radioactive material remains.
After permanent seed implants
Permanent seeds are tiny sealed capsules — the American Cancer Society (ACS) describes each as "about the size and shape of a grain of rice", with "around 100 seeds" placed in a typical prostate implant, depending on prostate size. They contain isotopes such as iodine-125 or palladium-103 and are left in place for life. For the full procedure, see our guide to life after prostate seed implants.
The radiation from these isotopes is low-energy and travels only a short distance, so most of it is absorbed inside the prostate. A University of Washington Medicine patient leaflet explains that very small amounts can still reach other people, and that "the amount that escapes is so small that it is not considered a risk for most people." The extra caution is for groups considered more sensitive to radiation.
Close contact, pregnant partners and children
Every official source we reviewed agrees on the principle: limit prolonged close contact with pregnant people and young children for the first weeks or months. The NCI advises being "extra careful not to spend time with children or pregnant women" when a permanent implant is first placed. The ACS says your doctor may advise you to stay away from pregnant women and small children while the seeds are most active.
What this usually means in practice is distance and time, not isolation. Macmillan says it is safe to be in the same room, but to keep a set distance and avoid holding or hugging children or pregnant people for more than a few minutes each day. One NHS trust (United Lincolnshire Hospitals) tells patients that for the first two months they may greet pregnant women "as normal and spend time in the same room", but should not sit closer than 0.5 metres.
If your partner is pregnant, or could become pregnant, tell your team. The same NHS leaflet asks patients whose partner is or becomes pregnant to contact the department so the risk can be assessed, and advises against fathering a child in the first two years after the implant.
Sleeping, hugging and pets
Sleeping in the same bed with a non-pregnant adult partner is described as safe by the hospital leaflets we reviewed. Alberta Health Services (Canada) suggests placing a pillow between you for the first 60 days to keep a little space.
Hugging is generally fine. The Alberta leaflet says "You can visit and hug people after your implant"; what centres restrict is long close contact, such as a child sitting on your lap.
Pets are rarely mentioned in official guidance. Of the sources we checked, only the Alberta leaflet addresses them, grouping pets with children: avoid having pets or kids sit on your lap for 2 months (60 days). If you have a pet that sleeps on you, ask your team.
How long precautions last (half-life explained simply)
A seed's radioactivity halves every half-life: about 60 days for iodine-125 and about 17 days for palladium-103 (values published in the Journal of Medical Physics). That is why precaution periods are measured in weeks or months, and why they differ by isotope. Using that half-life, our own arithmetic for iodine-125 seeds looks like this:
| Time after implant (iodine-125) | Approx. activity remaining | What centres typically say at this stage |
|---|---|---|
| 2 months | ~50% | End of the close-contact precautions in the UK and Canadian leaflets we reviewed |
| 4 months | ~25% | End of the close-contact precautions in the University of Washington leaflet |
| 1 year | ~1.5% | UW Medicine: "By 1 year, the radioactivity is essentially gone" (I-125) |
| 20 months | <0.1% | Alberta: "no radioactivity left in the seeds"; Leeds: pelvic surgery, post-mortem and cremation can go ahead without contacting the team |
Palladium-103 fades faster: the UW Medicine leaflet says it "releases 90% of its radioactivity within 2 months" and that by 4 months "its radioactivity is essentially gone".
Seeds passed in urine or semen: what centres instruct
Occasionally a seed can come out, usually in the first days or weeks. Instructions for what to do differ more than any other topic:
- Urine. The ACS says patients may be asked to strain their urine for about the first week. UW Medicine asks patients to strain urine for the first week and return any seed in the packet provided. United Lincolnshire Hospitals sieves urine only during the hospital stay; at home, a seed should be picked up with spoons or long tweezers (never with fingers) and flushed away. Alberta also says to flush it and call the brachytherapy office.
- Semen. Condom advice ranges from 1–2 weeks (UW Medicine) and 2–4 weeks after an initial 2-week pause (Alberta) to "the first 2 months" (Macmillan) or "the first five ejaculations" after a 2-week pause (United Lincolnshire). Dark brown or black semen for a few weeks is described as normal bleeding from the procedure.
- Body waste and objects. Urine and stools are not radioactive, and things you touch do not become radioactive, according to both the UW and United Lincolnshire leaflets.
Passing a seed does not usually mean the treatment has failed: United Lincolnshire tells patients that enough radiation remains in the prostate to treat the cancer. Always tell your team if you think you have passed one.
How four hospitals word the same advice
Hospital pages online usually give one or two lines. Below, we put the written instructions of four real centres side by side for iodine-125 prostate seeds. The point is not to pick a "right" answer: it is to show why you should follow the leaflet your own centre gives you, since details vary with isotope, implant activity and local rules.
| Topic | Alberta Health Services (Canada) | United Lincolnshire Hospitals NHS (UK) | UW Medicine (US) | Leeds Teaching Hospitals NHS (UK) |
|---|---|---|---|---|
| Pregnant people & children | Arm's length, 2 months | Not closer than 0.5 m, 2 months | At least 6 feet in the same room, 4 months | Follow leaflet advice for the first 2 months |
| Child on lap | Avoid (kids and pets), 2 months | Avoid for any length of time; brief cuddles standing are fine | Not for 4 months | — |
| Sharing a bed | Safe; pillow between you for 2 months | Safe if partner is not pregnant | No restrictions with sexual partner | — |
| Sex / condoms | No sex 2 weeks; condom 2–4 weeks | No sex 2 weeks; condom for first 5 ejaculations | Condom 1–2 weeks | Follow leaflet advice |
| Seed passed | Flush it; call the office | Spoon/tweezers, flush; tell the team | Strain urine 1 week; return the seed | Spoon/tweezers, flush |
| Implant card carried for | 20 months | 2 years | Letter on request for travel | 3 years |
| Travel | Avoid plane/bus trips for 1 month if possible | No restrictions with most adults | Travel as usual | Card explains detector alarms |
While you are in hospital with a temporary implant
Some low-dose-rate or pulsed-dose-rate treatments keep a source inside you for hours or days, usually in hospital. During that time — and only then — visitors may be limited. The NCI lists measures such as a private room, visitors checking with staff before entering, standing by the doorway, visits of "about 30 minutes or less each day", and no visits from pregnant women or children younger than a year old. Macmillan notes you may be looked after in a single treatment room and may need to be alone at times.
These limits end when the source is removed. If you have HDR as an outpatient, there are usually no visitor restrictions at all, because the source is never in your body while you are with other people.
Airport and security alarms — wallet cards
Radiation detectors at airports, ports and some public buildings are sensitive enough to pick up permanent seeds, even though the levels are very low. The ACS says low levels "can sometimes be picked up by detection systems at airports" and suggests carrying a doctor's note. The Leeds Teaching Hospitals card leaflet adds that such detectors may set off an alarm "even though the radiation levels are very low".
Centres solve this with an implant card or letter. It typically records the isotope, implant date and a contact number, and you show it to security staff if an alarm sounds. The same card matters if you need surgery or emergency care, and your next of kin should know about it. Leeds and United Lincolnshire both note that cremation within the card period needs special arrangements, so the card should be kept with your important papers.
After HDR or a removed temporary implant, there is nothing to detect, and no card is needed for radiation purposes.
The regulations behind release from hospital
These instructions are not just local habit; they come from radiation-protection law.
United States: NRC 10 CFR 35.75
Under the US Nuclear Regulatory Commission rule 10 CFR 35.75, a licensee may release a patient with an implant if the total effective dose to any other person "is not likely to exceed 5 mSv (0.5 rem)". If the dose to another person is likely to exceed 1 mSv (0.1 rem), the patient must receive instructions, "including written instructions", on how to keep doses to others as low as reasonably achievable. The rule also requires breast-feeding guidance where a nursing infant or child could exceed 1 mSv, and records of the basis for release.
United Kingdom: IR(ME)R 2017
In the UK, regulation 12 of the Ionising Radiation (Medical Exposure) Regulations 2017 requires that, where appropriate, patients treated with radioactive substances receive written instructions. These must explain how doses to people in contact with the patient can be restricted, set out the risks of ionising radiation, and be given before the patient leaves the place where treatment was carried out.
That is why your leaflet exists, and why it is specific to your implant: it is how your centre meets these duties for your particular isotope and activity.
Table: precautions by implant type
A one-page summary you can print and share with family. Print with your browser (Ctrl/Cmd + P).
| Implant type | Radioactive after you go home? | Precautions for others | Implant card? |
|---|---|---|---|
| HDR brachytherapy (any site: prostate, cervix, vaginal cuff, breast, skin…) | No | None after each session | No |
| Temporary LDR or PDR implant (hospital stay) | No, once removed | Visitor limits only while the source is in place | No |
| Permanent seeds (mainly prostate; iodine-125, palladium-103) | Yes, low and fading over months | Limit prolonged close contact with pregnant people and young children for the period on your leaflet; seed and condom advice | Usually yes, for the period your centre states |
| Radioisotope therapy (unsealed medicines — not brachytherapy) | Body fluids may be, for a time | Separate rules: toilet hygiene, close contact | Depends on treatment |
Always follow your own centre's written instructions
The table of four hospitals shows the same isotope producing 2-month and 4-month precaution periods, and condom advice from 1 week to 2 months. None of these is "wrong": each centre sets its advice from its own implant activities, measurements and regulator. That is also why no website — including this one — can tell you exactly when your precautions end.
Practical steps that help:
- Ask for the written instructions before the day of the implant, so family members can read them too.
- Write down the end date of each precaution on your calendar.
- Tell your team about anyone close to you who is pregnant, planning a pregnancy, or a young child you care for regularly.
- Keep the implant card in your wallet and tell your next of kin where it is.
Worried about discomfort rather than radiation? See is brachytherapy painful. If something in this guide is unclear, you can ask us a question — we answer with sources, not personal medical advice.
Frequently asked questions
Am I radioactive after HDR brachytherapy?
No. In HDR brachytherapy the source is removed at the end of each session. The National Cancer Institute states there is no radiation in your body after the catheter or applicator is removed, and that it is safe for people to be near you, including young children and pregnant women.
Can I be near a pregnant woman after prostate seed brachytherapy?
Yes, with limits for a period. Macmillan says it is safe to be in the same room but to keep a set distance and avoid prolonged close contact. The leaflets we reviewed set this period at 2 months or 4 months for iodine-125 seeds. Follow your own centre's written instructions.
Can I hold my grandchild after seed implants?
Brief contact is generally allowed, but long close contact such as a child sitting on your lap is usually avoided for the first months. One NHS trust allows cuddling a child at chest level while standing for a few minutes each day. Your own centre will tell you how long this applies.
Are pets at risk from brachytherapy seeds?
Official sources rarely mention pets. One Canadian hospital leaflet (Alberta Health Services) advises avoiding pets or children sitting on your lap for 60 days after an iodine-125 implant. After HDR or a removed temporary implant, there is no source in your body, so no pet precautions are needed.
Will brachytherapy seeds set off airport alarms?
They can. The American Cancer Society says low levels of radiation can sometimes be picked up by airport detection systems. Centres give an implant card or letter to show security staff. After HDR or a removed temporary implant there is nothing to detect.
Is my urine radioactive after seed implants?
No. Hospital leaflets from UW Medicine and United Lincolnshire Hospitals state that urine and stools are not radioactive. The only concern is a seed occasionally passing out, usually in the first days. Centres differ on whether you should strain urine; follow your own instructions.
Sources
- National Cancer Institute — Brachytherapy to Treat Cancer (accessed 9 October 2026)
- Macmillan Cancer Support — Internal radiotherapy (accessed 9 October 2026)
- Macmillan Cancer Support — Brachytherapy for prostate cancer (accessed 9 October 2026)
- American Cancer Society — Radiation Therapy for Prostate Cancer (accessed 9 October 2026)
- US Code of Federal Regulations (eCFR) — 10 CFR 35.75 Release of individuals containing unsealed byproduct material or implants containing byproduct material (accessed 9 October 2026)
- legislation.gov.uk — The Ionising Radiation (Medical Exposure) Regulations 2017, regulation 12 (accessed 9 October 2026)
- Kehwar TS. Use of Cesium-131 radioactive seeds in prostate permanent implants. J Med Phys. 2009;34(4):191-193 (half-life values) (accessed 9 October 2026)
- Alberta Health Services (Cancer Care Alberta) — LDR brachytherapy for prostate cancer: permanent iodine-125 seed implant (patient leaflet, PDF) (accessed 9 October 2026)
- United Lincolnshire Hospitals NHS Trust — Prostate Seed Brachytherapy (patient leaflet 2236 v2, PDF) (accessed 9 October 2026)
- UW Medicine Urology and Prostate Clinic — Radioactive Seed Implant: after your treatment for prostate cancer (PDF) (accessed 9 October 2026)
- Leeds Teaching Hospitals NHS Trust — Your Prostate Implant Card (LN003722, PDF) (accessed 9 October 2026)
Educational content. It does not replace advice from qualified healthcare professionals. Your own treatment team is the right source for decisions about your care. Written by the brachytherapist.com editorial team from the sources listed above. Hospital leaflets are quoted as examples of real-world instructions, not as recommendations for your care.