Permanent prostate brachytherapy (seed implant) is a prostate cancer treatment that uses ionizing radiation to destroy cancer cells. The radioactive material is placed either directly into a malignant tumor or very close to it, thus the term brachytherapy, which means short therapy in Greek. Radiation kills the tumor by destroying the DNA within the cancer cell. When the cancer cell attempts to divide and reproduce itself, it is unable to do so because the DNA is no longer intact and as a result, the prostate cancer dies.
In 1916, the first prostate brachytherapy procedure was performed. Over the past twenty years, technology has resulted in dramatic advancements of prostate brachytherapy. Improved ultrasound equipment used to visualize the prostate and precisely guide the placement of radioactive seeds allows for the delivery of a very high dose of radiation to the prostate, while minimizing the dose to the surrounding normal body organs such as the bladder and rectum. As a result, prostate brachytherapy has become very popular as a treatment option for patients diagnosed with early-stage prostate cancer.
What is involved with prostate cancer treatment?
Ultrasound images (volume study) allow a physician to determine the exact shape and size of the prostate gland. Outlining the area of the prostate gland where the cancer was identified on biopsy also assists physicians in treatment planning.
These pictures are then reconstructed on a three-dimensional treatment planning computer and allow the physician to determine exactly how many seeds are needed and where they should be placed within the prostate gland and in relation to the urethra, bladder, and rectum.
The treatment plan for prostate cancer
Each seed implant is individually planned to determine the optimal distribution of radiation. The radiation oncologist and a team of medical physicists are specially trained to understand the best dose of radiation to give to the prostate while also protecting the rectum and bladder from radiation. A permanent prostate seed implant is performed using cesium (cs131), iodine (i125) or palladium (pd103) in the form of small radioactive seeds.
Since they are located close to or within the cancer, the radioactive seeds can deliver a significant amount of radiation in an area no larger than a centimeter, while the adjacent area receives minimal, if any, radiation. A physician can therefore implant high doses of radiation into the prostate while avoiding normal critical structures such as the bladder and rectum.
When is brachytherapy appropriate?
Typically, the best candidate for brachytherapy is someone with a prostate tumor confined to the prostate gland that has a very low risk of spreading to other parts of the body. This is referred to as monotherapy (or one treatment).
Brachytherapy is also the preferred treatment for those with intermediate or high-risk prostate cancer. The seed implant is often performed in combination with external beam radiation therapy, plus or minus hormone therapy. This is referred to as combination therapy. Your physician will help guide you towards the most appropriate treatment plan.
Brachytherapy is not appropriate in patients whose cancer has already spread beyond the prostate and into other areas of the body. Patients who have had a transurethral resection of the prostate (turp) may have brachytherapy, however, they will need to meet certain criteria.
How much radiation will I receive?
The total amount of radiation the prostate gland will receive depends upon the amount of radiation in each seed and the total number of seeds deposited. A typical implant usually requires approximately 60 to 100 seeds, depending on the size and shape of a patient’s prostate gland. The extent of treatment that a patient requires is dependent upon the risk that his cancer is confined to the prostate. As a rule, low-risk patients require one treatment, such as permanent seed implant. Hormone therapy in this group of patients may be used to reduce the overall size of a large prostate gland.
It is often recommended that men at intermediate risk for cancer that has spread undergo more aggressive treatment. At a minimum, this means a combination of hormone therapy plus a seed implant. In some cases, even more aggressive measures, such as adding five weeks of external beam radiation therapy (EBRT) to a seed implant, may be indicated. The purpose of the additional EBRT is to kill any cancer cells that may have escaped the prostate and are in the tissue around the prostate. High-risk patients can also benefit from brachytherapy, but this is usually done in combination with EBRT and hormone therapy.