Permanent prostate brachytherapy (seed implants) 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.
Doctors used brachytherapy to treat prostate cancer as long ago as the early 1900s. In fact, in 1906, Alexander Graham Bell argued in support of this very point. 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. The development of computer systems, has allowed even more precise brachytherapy. As a result, prostate brachytherapy has become very popular as a treatment option for patients diagnosed with early stage prostate cancer.
What Is Involved?
Ultrasound images (volume study) allow a physician to determine the exact shape and size of the prostate gland. This is not unlike having a suit made; the tailor must first measure the chest, arm length, and inseam so that he can make the material to custom-fit the customer's body. 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
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.
As they are located close to or within the cancer, the radioactive seeds are able to 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.
Typically, patients arrive one hour before the procedure. A clear liquid diet and laxative is required the day before and nothing should be eaten by mouth after midnight on the day of the procedure. These recommendations minimize gas and allow better visualization of the prostate gland.
In the operating room, the placement of needles that contain the radioactive seeds is guided by the use of ultrasound and fluoroscopy.
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.
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 Is Enough?
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.
While the physical properties of radioactive isotopes will remain the same, prostate brachytherapy will only improve as technology evolves. Furthermore, as clinical studies mature and the data is analyzed, physicians in the field will be better prepared to identify more precisely the specific criteria that will allow even better patient selection for prostate brachytherapy.