Brachytherapy is a form of radiation treatment in which radioactive seeds are placed directly into the prostate with the purpose of destroying the cancer. The seeds are placed into the prostate using needles guided by an ultrasound probe. Each seed is approximately the size of a poppy seed and between 80 and 120 seeds are permanently implanted into the prostate gland.
The seeds release radiation gradually over a 6 to 12 month period before losing their entire radioactivity.
The goal of seed implantation is to eliminate the cancer before it can spread to other parts of the body. The best candidates for seed implantation are men with small, organ confined slow growing cancers who have a normal sized prostate gland, normal urinary and bowel function and no previous prostate surgery.
The Seed Implant Procedure
Seed implantation involves several phases:
- Planning the procedure
- Implanting the seeds
- Evaluating the ‘quality of the implant’
The success of an implant depends upon accurate seed placement throughout the prostate gland. This requires an accurate 'map' of the prostate which is obtained by performing an MRI scan of the prostate .Once this study has been performed the information obtained is used by a radiation physicist and radiation oncologist to create a 'dosimetry plan'. This plan specifies the number and position of the seeds that will provide the proper dose of radiation to the prostate gland.
This is performed by the urologist and radiation oncologist in an operating theatre while the patient is under a general anaesthetic. The dosimentry plan is followed and the seeds are implanted into the prostate by guiding long needles containing the seeds through the perineum and into the prostate gland. This usually takes between 45 minutes to perform. Following implantation the patient returns to the ward and is discharged home the following day.
After the implant a CT scan is performed to assess seed location and to calculate the actual radiation dose delivered to the prostate gland.
Side Effects and Complications of Seed Implants
For the first few days following the implant patients experience side effects due to the fact that a catheter that has been inserted and the prostate has had needles inserted into it. These symptoms usually consist of a burning sensation when urinating, some blood or small clots in the urine and some bruising between the legs.
Beyond the immediate recovery period urinary symptoms such as frequency, urgent urination and slow urination peak at around 3 to 8 weeks after the implant. These symptoms are due to the effect of the radiation on the prostate and they usually take 6-10 months to resolve. Approximately one in thirty men will require a temporary catheter (A catheter is a small rubber tube inserted through the penis into the bladder to drain urine, usually into a small plastic bag strapped to the leg under the pants.) due to prostate swelling causing an inability to urinate. A minority of patients are left with bothersome urinary symptoms in the long term. Temporary painless urethral bleeding may occur 1-2 years post implant. This is due to radiation damage to blood vessels in the prostate. It usually resolves without requiring specific treatment. Urethral stricture is a rare but serious complication of prostate brachytherapy. Dense scar tissue can obstruct the urethra - this can be very difficult to treat and may require major surgery or long term catheterisation.
Sexual function following seed implantation depends upon the patients level of function pre-operatively. Impotence occurs in 50% of men and is due to radiation damage to the nerves controlling erection which pass close by the prostate gland. This damage tends to accrue slowly over several years.
Rectal complications are uncommon. Temporary painless rectal bleeding occurs in about 5% of cases; this can occur from 6-18 months following treatment and can last from a few weeks to a few months. Severe rectal injury is very uncommon however a severe radiation injury may lead to formation of a fistula (communication between the rectum and urethra) which may require major surgery, usually the formation of a permanent colostomy and/or urostomy.
Most of the radiation from an implant is confined to the prostate itself. A small amount of radiation will be found at the skin surface over the lower abdomen. Because of this men are cautioned against prolonged close contact with children less than two years of age and with pregnant women for the first two months following the implant.
PSA levels are taken every six months following the implant. The PSA level should slowly fall over many months indicating that the cancer has responded to the radiation.