Prostate Cancer Seed Implants (Brachytherapy)

HOW BRACHYTHERAPY WORKS

Radioactive Sources

There are two types of radioactive materials (radioisotopes) that can be implanted into the prostate: Iodine (I-125) and palladium (Pd-103). They are carried within identical 5 millimeter x 1 millimeter titanium canisters that are called “seeds”. The selection of one type of seed over the other for a particular patient is typically based on hypothetical biological advantages offered by either seed for a given set of circumstances. Iodine is frequently chosen for those cancers that are less aggressive, and palladium is reserved for the more aggressive tumors. Both types of seeds offer continuous low dose rate, low energy irradiation of the cancer.

Mechanism Of Cancer Cell Kill

The radiotherapy derived from the seeds kills cancer cells by way of DNA damage such that the tumor cells die as they try to grow. When enough damage accumulates in the cancer cell, it is no longer viable and will break apart as it attempts to split into two new cancer cells. Normal tissues commonly recover from DNA damage and are spared the killing effect.

Preimplant Procedure/Screening

Prostate cancers that are eligible for seed implantation must fall within a set of guidelines established by the treating radiation oncologist and the urologist. These guidelines are basic rules that help sort out candidates for the procedure versus those patients who may be best suited for an alternative therapy. A final recommendation is made after considering a patient’s age, daily activity level, cancer status, urinary history, medical history, and quality of life concerns. Some of the issues which are considered are the size of the prostate, tumor grade, tumor stage, PSA level, and any history of prior prostate surgeries. Those patients who are ineligible for brachytherapy may be offered high dose Three-Dimensional Conformal Radiotherapy.