If your oncologist has mentioned brachytherapy, you have probably also heard the letters HDR and LDR. Both are forms of brachytherapy, or internal radiotherapy: a radioactive source is placed inside or right next to the tumour instead of aiming beams from outside the body.
The difference is how fast the radiation dose is delivered. That one difference drives everything you will notice as a patient: how many visits you make, whether you stay overnight, whether anything radioactive stays in your body, and whether you need precautions around other people afterwards.
This guide puts both types side by side across tumour sites, explains the less-discussed options (pulsed-dose-rate and the "boost"), and ends with questions you can take to your team. It is general information, not advice about your own treatment.
The short answer
HDR brachytherapy uses a single, highly active source that a machine sends into thin tubes or an applicator for a few minutes and then pulls back. The US National Cancer Institute (NCI) describes the source being left in place "for just 10 to 20 minutes at a time and then taken out". Treatment is usually split into several sessions.
LDR brachytherapy uses sources with much lower activity. They either stay in for a period of hours to days (a temporary LDR implant, usually with a hospital stay) or stay in the body permanently as tiny "seeds" that slowly lose their radioactivity. Permanent seed implants are best known in prostate cancer.
What "dose rate" means (no maths needed)
Radiation dose is measured in grays (Gy). The dose rate is simply how much of that dose arrives per unit of time — like the difference between filling a bucket with a fire hose for a few minutes or with a dripping tap over many days.
The total dose your team prescribes is planned so that the tumour gets enough radiation while nearby organs (for example the bladder, rectum or urethra) get as little as possible. HDR reaches its planned dose in minutes; LDR spreads its dose over a much longer time.
LDR brachytherapy: permanent seeds and temporary low-dose implants
"LDR" covers two quite different patient experiences, which is a common source of confusion:
- Permanent LDR (seed implant). Tiny sealed seeds are left in the tissue for good. RadiologyInfo (from the American College of Radiology and the Radiological Society of North America) describes them as "about the size of a grain of rice". The American Cancer Society notes that in prostate cancer "usually, around 100 seeds are placed, but this depends on the size of the prostate".
- Temporary LDR. A source sits in an applicator or tubes for a set time and is then removed. The NCI says that with LDR "the radiation source stays in place for 1 to 7 days", usually with a hospital stay. RadiologyInfo describes continuous delivery over one to two days with an overnight stay.
Which sources are used
For permanent prostate seed implants, the joint American Society of Clinical Oncology / Cancer Care Ontario guideline (2017 update) states that iodine-125 and palladium-103 "are each reasonable isotope options", and that no recommendation could be made for or against cesium-131. RadiologyInfo lists iodine, palladium, cesium and iridium as the materials used across brachytherapy, depending on the treatment.
What happens to the seeds over time
This is the answer to the common search "how long does brachytherapy stay in the body". Permanent seeds stay for life, but their radioactivity falls by half every half-life. NCI puts it plainly: "the radiation gets weaker each day" and "almost all the radiation will go away". RadiologyInfo says that after several months the seeds lose their radioactivity.
Using the half-lives published in the Journal of Medical Physics (about 60 days for iodine-125, 17 days for palladium-103 and 9.7 days for cesium-131), simple arithmetic shows how quickly activity falls:
| Seed isotope | Half-life | Left after 1 month | After 3 months | After 6 months | After 1 year |
|---|---|---|---|---|---|
| Iodine-125 | ~60 days | ~71% | ~35% | ~12% | ~1.5% |
| Palladium-103 | ~17 days | ~29% | ~2.5% | <0.1% | ≈0% |
| Cesium-131 | ~9.7 days | ~12% | ~0.2% | ≈0% | ≈0% |
This is why precautions after seed implants are time-limited and why their length can differ by isotope. For what that means in practice at home, read our guide on brachytherapy radiation and family, and for the full prostate pathway see prostate seed brachytherapy: what to expect.
HDR brachytherapy: the afterloader and short sessions
HDR is always temporary. Cleveland Clinic states that "HDR treatments are always temporary, so your provider removes the implant after each session." Hollow needles, catheters or an applicator are positioned first, the team checks their position with imaging and plans the dose, and only then is the source sent in.
What an afterloader is
An afterloader is the computer-controlled machine that stores the source in a shielded safe and moves it, on a thin cable, into each tube for a planned number of seconds at each position. It is called "after"-loading because the applicator goes in first and the radioactive source is loaded afterwards, while staff wait outside the treatment room. RadiologyInfo notes that the machine "stores a powerful source" of iridium-192. When the session ends, the source returns to the safe.
How many sessions?
There is no single number. The sources give ranges rather than rules:
- NCI: treatment "twice a day for 2 to 5 days or once a week for 2 to 5 weeks".
- RadiologyInfo: "up to 10 separate HDR treatments over one or more weeks", usually as an outpatient, though some people are admitted for one to two days so that several treatments can use the same applicator.
- Prostate (American Cancer Society): "about 1 to 4 brief treatments are given over 2 days", with the source in place usually for 5 to 15 minutes.
- Cervix (American Cancer Society): HDR is "an outpatient procedure over several treatments (often at least a week apart)".
Remember that "session" means time with the source inside you. The whole visit — applicator placement, imaging, planning and removal — usually takes much longer than the 10–20 minutes of actual irradiation. For a site-specific walk-through, see HDR brachytherapy for cervical cancer.
PDR (pulsed-dose-rate) in brief
PDR is a hybrid that most patient pages skip. It uses an afterloader like HDR, but instead of a few big sessions it delivers small "pulses" — RadiologyInfo says usually one per hour — around the clock for a period, which imitates the continuous effect of LDR. Because the applicator stays in between pulses, PDR typically means a hospital stay. Macmillan Cancer Support lists HDR, PDR and LDR as the options for gynaecological brachytherapy and notes that "these methods all work equally well" and that "the type you have depends on the system your hospital uses".
Side-by-side table: HDR vs LDR vs PDR
| HDR (high-dose-rate) | Temporary LDR | Permanent LDR (seeds) | PDR (pulsed) | |
|---|---|---|---|---|
| How the dose arrives | Minutes per session, source removed each time | Continuous, low, for hours to days | Continuous, low and falling over weeks to months | Hourly pulses over a period |
| Typical number of sessions | Several (ranges from 1–4 for prostate to up to ~10 overall, per source) | Usually one insertion | One implant procedure | One insertion, many pulses |
| Hospital stay | Often outpatient; sometimes 1–2 days | Usually yes (1–7 days per NCI) | Varies with the anaesthetic used and the centre — ask your team | Usually yes |
| Radioactive source in you after you go home? | No | No (removed before discharge) | Yes, low and decreasing | No |
| Precautions around others at home | None from the source | None once removed | Time-limited written precautions, e.g. around pregnant people and young children | None once removed |
| Visitors during treatment | Not usually relevant: the source is in for minutes and staff watch from outside the room | Restricted while source is in | Close-contact precautions may apply for a time (see above) | Restricted while source is in |
| Common uses mentioned by sources | Prostate (alone or as a boost), cervix and other gynaecological cancers | Some prostate and eye cancers (Cleveland Clinic); gynaecological cancers where the centre uses LDR (Macmillan) | Prostate (best known) | Gynaecological cancers where the centre uses PDR (Macmillan) |
| Source examples | Iridium-192 | Varies | Iodine-125, palladium-103, cesium-131 | Iridium-192 |
Sources for this table: NCI, RadiologyInfo, Cleveland Clinic, Macmillan, American Cancer Society and the ASCO/CCO guideline (full links below). Ranges vary by centre.
What is an "HDR boost"?
A boost is an extra, highly targeted dose of brachytherapy added to a course of external beam radiotherapy. It is common in cervical and prostate cancer. The American Cancer Society says that for cervical cancer "brachytherapy mainly is used in addition to EBRT". For prostate cancer, the ASCO/CCO guideline recommends offering an LDR or HDR brachytherapy boost to eligible patients with intermediate- or high-risk disease who are having external beam radiotherapy. We explain how the two treatments fit together in brachytherapy compared with external beam radiotherapy.
Who decides which type — and why centres differ
The choice is made by your radiation oncologist with the wider team — medical physicists, dosimetrists, radiation therapists and nurses. Several factors come into it:
- The tumour and its risk group. For prostate cancer, the ASCO/CCO guideline suggests LDR alone for some low and low-intermediate risk situations, while it could make no recommendation for or against HDR used alone (monotherapy) on the evidence it reviewed.
- Anatomy and history. The American Cancer Society notes brachytherapy "might not work as well for men with large prostate glands", and urinary side effects may be more likely after a previous TURP or with existing urinary problems.
- Other treatments. Whether brachytherapy is the whole treatment or a boost after external beam radiotherapy.
- The centre itself. An HDR or PDR service needs an afterloader, shielded rooms and in-room imaging; a seed programme needs a seed supply chain and specific planning experience. Many centres concentrate on one technique, which is why Macmillan says the type "depends on the system your hospital uses".
Questions to ask your team about HDR or LDR
- Will my brachytherapy be HDR, LDR (temporary or permanent seeds) or PDR — and why that type for me?
- Is brachytherapy my whole radiotherapy, or a boost after external beam treatment?
- How many sessions or procedures will I have, over how many days or weeks?
- Will I need a general or spinal anaesthetic, sedation, or none?
- Will I stay in hospital? For how long, and can I have visitors?
- Will anything radioactive stay in my body? If so, what written precautions will I get, and for how long?
- How many of these procedures does this centre do each year, and who will be in the room?
- What side effects are most likely with this type for my cancer, and when should I call you?
Print-friendly versions of these and more are in our brachytherapy question checklist.
FAQ
Is HDR or LDR brachytherapy better?
Neither is better in general. They are two ways of delivering internal radiotherapy, and which one is used depends on the cancer, its risk group, the anatomy, other treatments planned and what the centre is equipped and experienced to offer. For cervical cancer, Macmillan Cancer Support states that HDR, PDR and LDR all work equally well and the type depends on the system your hospital uses.
Am I radioactive after HDR brachytherapy?
No. In HDR brachytherapy the source is removed at the end of every session. The US National Cancer Institute states that there is no radiation in your body after the catheter or applicator is removed.
How long do LDR prostate seeds stay radioactive?
The seeds stay in the body for life but their radioactivity fades steadily. RadiologyInfo states that after several months the seeds lose their radioactivity. How fast depends on the isotope: iodine-125 has a half-life of about 60 days, palladium-103 about 17 days and cesium-131 about 9.7 days.
How many sessions of HDR brachytherapy will I need?
It varies by cancer and centre. RadiologyInfo says patients may receive up to 10 separate HDR treatments over one or more weeks, and the National Cancer Institute describes schedules of twice a day for 2 to 5 days or once a week for 2 to 5 weeks. Your team will give you your own schedule.
What is an HDR brachytherapy boost?
A boost is an extra dose of radiation given with brachytherapy on top of a course of external beam radiotherapy. In prostate cancer the ASCO/Cancer Care Ontario guideline recommends offering an LDR or HDR brachytherapy boost to eligible patients with intermediate- or high-risk disease who are having external beam radiotherapy.
Sources
- National Cancer Institute — Brachytherapy to Treat Cancer (accessed 9 October 2026)
- RadiologyInfo.org (ACR/RSNA) — Brachytherapy (accessed 9 October 2026)
- Cleveland Clinic — Brachytherapy (accessed 9 October 2026)
- Macmillan Cancer Support — Internal radiotherapy (accessed 9 October 2026)
- Chin J, et al. Brachytherapy for Patients With Prostate Cancer: ASCO/Cancer Care Ontario Joint Guideline Update. J Clin Oncol. 2017;35(15):1737-1743 (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)
- American Cancer Society — Radiation Therapy for Prostate Cancer (accessed 9 October 2026)
- American Cancer Society — Radiation Therapy for Cervical Cancer (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.