Brachytherapy is a form of radiation therapy that treats prostate cancer from the inside, placing radioactive material directly into or next to the prostate gland. Because the radiation source sits millimeters from the tumor rather than passing through the body from an external machine, it delivers a high dose to the cancer while exposing the bladder, rectum, and urethra to considerably less radiation. There are two main types, and which one you receive depends largely on how aggressive your cancer is.
How LDR and HDR Brachytherapy Work
Low dose rate (LDR) brachytherapy, often called a “seed implant,” involves permanently placing tiny radioactive seeds into the prostate through needles inserted through the skin between the scrotum and rectum. These seeds, typically made with iodine-125, emit radiation slowly over weeks to months at less than 2 Gy per hour. They stay in the body permanently but become inactive once their radioactive material decays.
High dose rate (HDR) brachytherapy takes the opposite approach. Thin catheters are temporarily inserted into the prostate, a high-activity radioactive source (usually iridium-192) travels through those catheters to deliver radiation at rates often exceeding 1 Gy per minute, and then everything is removed. Nothing is left behind. HDR generally produces more consistent dose coverage across the gland and delivers relatively lower doses to the rectum, bladder, and urethra compared to LDR.
Who Qualifies for Brachytherapy
LDR brachytherapy as a standalone treatment works best for low-risk prostate cancer. European and American guidelines define this as a clinical stage between T1c and T2a (cancer confined to the prostate), a Gleason score of 6 or lower, a PSA under 10 ng/mL, and no more than 50% of biopsy cores containing cancer. The American Brachytherapy Society also considers HDR monotherapy an option for low-risk patients.
For intermediate-risk disease (Gleason 7 or PSA between 10 and 20 ng/mL), brachytherapy is typically used as a “boost” combined with external beam radiation, sometimes alongside short-term hormone therapy lasting four to six months. For high-risk patients, the combination of external radiation plus permanent seed implant is considered a standard approach. HDR boost is specifically recommended for intermediate and high-risk patients as a dose escalation technique.
Prostate size matters. A gland volume over 60 cubic centimeters is a relative contraindication because the prostate may be too large for the implantation template or may be blocked by the pubic bone. If your prostate exceeds this threshold, your doctor may prescribe hormone therapy for two to three months to shrink it before proceeding. For glands over 100 cc, brachytherapy is generally discouraged regardless of whether hormone therapy is used.
What the Procedure Looks Like
LDR seed implantation is typically done under general or spinal anesthesia as an outpatient procedure. Using ultrasound guidance, the physician places 40 to 100 or more seeds through a grid template pressed against the perineum. The whole process usually takes one to two hours. Most people return to their normal routine within one to two days, though activities that put pressure on the groin, like cycling or horseback riding, should be avoided for about two months.
HDR treatment involves a similar needle placement, but instead of leaving seeds behind, the catheters are connected to a machine that advances a single radioactive source through each catheter in a precisely timed sequence. A randomized trial comparing HDR monotherapy schedules found that two fractions of 13.5 Gy delivered one week apart provided durable cancer control at eight years and was well tolerated. A single fraction of 19 Gy, by contrast, showed poor cancer control and is no longer recommended.
Cancer Control and Long-Term Outcomes
A 10-year follow-up study comparing treatment approaches for localized prostate cancer found that brachytherapy patients had a 78.1% overall survival rate at ten years, compared to 85.3% for radical prostatectomy. The difference partly reflects patient selection, since surgical candidates tend to be younger and healthier. Brachytherapy showed a lower rate of biochemical recurrence (a rising PSA suggesting the cancer may be returning) than external radiation alone, at 29.1% versus 43.0%, but a higher rate than surgery, at 29.1% versus 23.8%.
When brachytherapy is used as a boost alongside external radiation for higher-risk disease, the results improve substantially. The landmark ASCENDE-RT trial demonstrated that adding an LDR seed boost to external radiation significantly improved cancer control in intermediate and high-risk patients compared to external radiation alone.
Side Effects and Complications
About 55% of brachytherapy patients experience at least one urinary, rectal, or sexual side effect within two years of treatment. That number sounds high, but most of these are temporary irritative symptoms rather than serious complications. The rate of side effects severe enough to require an invasive procedure is much lower: 4.1% needed a procedure for erectile dysfunction, 0.8% needed a rectal procedure, and just 0.2% required treatment for urinary incontinence.
Urinary symptoms are the most common early complaint. Many men experience increased frequency, urgency, or a weak stream in the weeks following seed placement as the prostate swells from the implant. These symptoms typically peak around one to three months and gradually improve. Erectile function is better preserved with brachytherapy than with surgery overall, though some decline is common, particularly when hormone therapy is added to the treatment plan.
Radiation Safety After Seed Implants
After LDR brachytherapy, your body does emit a small amount of radiation. The practical risk to others is minimal. Calculations show that even in a worst-case scenario, a patient could hold a child on his lap for at least 30 minutes every day immediately after an iodine-125 implant without exceeding safety thresholds. Still, most clinicians advise limiting prolonged close contact with pregnant women and young children for the first few months as a precaution. HDR patients do not have this concern at all, since no radioactive material remains in the body after treatment.