Seattle Prostate Institute

About Seed Implantation -

THE SEED IMPLANT PROCEDURE

Seed implantation involves three distinct phases: planning the procedure, performing it, and evaluating it afterwards.

Procedure Planning: Since the success of an implant depends on the accurate placement of seeds throughout the prostate gland, the first step in the treatment process is the determination of the size and shape of the prostate. This is accomplished with an ultrasound "volume study", a relatively simple procedure that can be performed in a doctor’s office or the outpatient department of a hospital.

To carry out the volume study, an ultrasound probe is inserted into the rectum and moved along the length of the prostate, taking cross-sectional images every few millimeters. The special software built into the ultrasound equipment allows clinical staff to outline the prostate on each image. Using these electronic images, the software automatically calculates the volume of the prostate in cubic centimeters. A volume of 60 cc’s is generally considered the maximum size for a satisfactory implant to be performed.

The next step in planning an implant is identifying the "target volume", the area that must be covered, or targeted, by radiation. To do this, a radiation oncologist will take each of the volume study images and circle the area that should receive radiation. (Figure 9) In general, the target volume can extend beyond the prostate itself to include 2-5 millimeters of tissue surrounding the entire gland. Physicians include this "prostate margin" in the target volume in order to treat any microscopic cancer cells that may have spread to the tissue immediately outside the gland. Research has shown that this "capsular penetration" can occur in patients with very early stage disease. It is for this same reason that surgeons try to remove extra tissue from around the prostate when performing radical prostatectomies.