ProstRcision involves a two-step treatment process that specifically targets cancer cells within the prostate while minimizing potential side-effects. These two treatment steps overlap, which produces the dose intensification required to kill the cancer.
Actual size of an I-125 seed (right), used to radiate the cancer, and the gold seed (left) used as a target.
Our therapist preparing our linear accelerator for a patient’s daily treatment.
The ProstRcision procedure begins when a physician implants tiny radioactive seeds into the prostate. Since the seeds are only 1/5 of an inch in length, and as thin as a pencil lead, physicians can position them directly in the tumor and away from important muscles and nerves. These seeds emit most of their radiation over the course of a few months, but will continue to release radiation for up to one year. When we say ProstRcision can attack the cancer with pinpoint accuracy, it’s because the area surrounding the seeds is hit with a tremendous amount of radiation, but a few millimeters away, the radiation level drops off rapidly.
Since the prostate does not show up on an X-ray, the precisely placed radioactive seeds not only release radiation to kill the cancer, but they serve to map out the prostate so it can be seen on X-ray as well. In addition to these small silver seeds, physicians inject several slightly larger and thicker gold seeds into the prostate. These gold seeds also help to outline the prostate on X-rays, so the doctor can plan the second step of the ProstRcision process – the delivery of targeted irradiation.
Seed implants are an excellent way to destroy the cancer within a prostate, but they do have limitations. They don’t effectively kill any cancer that may have leaked outside the prostate (called microscopic capsule penetration). Further, because of the amount of close range radiation these seeds give off, they cannot be placed right next to the urethra without damaging it. Importantly, studies show that over 41% of men with prostate cancer have cancer on or near the urethra. This is why we follow the seed implant with another type of radiation called linear accelerator irradiation. The additional radiation delivered by an accelerator ensures that all the cells are killed within the prostate, because leaving even one cell, healthy or cancerous, could allow the cancer to come back over time.
One or two methods are used to deliver linear accelerator irradiation – either conformal beam (where the beam of radiation is shaped into an exact outline of each patient’s prostate) or the Intensity Modulated Radiotherapy Technique (IMRT). IMRT allows for better control over the dose of radiation and can potentially keep the nearby organs from being over-exposed, while focusing the radiation on the prostate.