Radioactive Seed Implant
The Brachytherapy Procedure in Detail
The sterilized needles containing the seeds are delivered to the operating room prior to the beginning of the procedure. If the procedure is done in a hospital, appropriate medical evaluation and clearance by the attending anesthesiologist occurs, the patient is then anesthetized and the procedure begins. If the procedure is done in our office, the nurse will start an IV and administer sedating medication under the supervision of the radiation oncologist, who will perform local anesthesia of the perineum and prostate using injected Xylocaine. This has become our standard anesthesia method, though general anesthesia in a hospital setting still occurs from time to time for a variety of reasons. The radiation oncologist and supporting staff perform the procedure, using ultrasound and CT guidance. At this time, due to logistical issues, CT-guidance is only used for office-based cases.
The seeds are contained within thin sharp hollow needles (FIGURE 12), which are inserted one at a time through the perineum (the patch of skin behind the scrotum), and advanced to prescribed position coordinates within the prostate, using real-time ultrasound-guided visualization of the needle as it advances through the prostate. A central stylette within the needle, spacing material between the seeds, and a plug at the end of the needle secure the seed “train” in proper position within the needle, until the moment of seed discharge.
During the procedure, the prostate and needles are normally easy to see with a trained eye, using ultrasound equipment that shows a “white” needle tip, guided through the “black” prostate tissue, to within 1-2 mm of a computer-prescribed prostate target coordinate. These target coordinates appear as a computer-generated dotted “grid” pattern on a television screen, referenced by letters on the X-axis and numbers on the Y-axis, with the ultrasound prostate image displayed relative to the grid pattern (FIGURE 13a). The depth of the needle insertion relative to the “X-Y” grid reference plane controls the Z-axis, resulting in full three-dimensional control of the final needle placement (FIGURE 13b).
After the needle tip has been guided to its final “X-Y-Z” computer-planned grid coordinate, its central stylette is then manually “frozen” in that position, and the hollow needle slowly withdrawn over the seed-stylette complex, leaving a row of seeds deposited along the resulting needle tract in its prescribed position, after which the needle and stylette are removed (FIGURE 13c). This guided-needle seed delivery procedure is repeated one needle at a time, carrying row after row of computer-designed seed patterns to their prescribed target locations, until a total of 30 or more guided needle punctures have been accomplished, and the entire targeted volume three-dimensionally implanted with the radioactive seeds.
The entire operating room procedure typically takes about 45-90 minutes, and the final effect is the creation of a seed pattern that results in a very high dose three-dimensional radiation volume within and immediately around the prostate, which is individually designed and customized for each patient (FIGURE 13d). The seeds remain permanently, but their internally contained radiation is spent over several months, leaving behind inert tiny titanium capsules within the prostate (FIGURE 14). The amount of radiation delivered to this volume over the entire lifetime of the radiation sources is normally lethal to all of the cancer cells contained within, but is simultaneously carefully designed to limit the radiation dose to the urethra, bladder and rectum, all of which also lie in close proximity to the prostate target volume.
At the end of the procedure a Foley catheter is placed through the penis and into the bladder (FIGURE 15). The Foley catheter is a small rubber tube that allows the bladder to drain properly, at a time when the prostate may be swollen, causing temporary obstruction of the urethra. The catheter tube comes out through the penis and is connected to a urine collection bag that is temporarily strapped to the lower leg and easily drained when it fills (commonly called a “leg bag”). The patient is discharged from the hospital after the effects of the anesthesia have worn off, typically one to two hours after the procedure has been completed. The Foley catheter is removed the following day, right after the CT-guided post-brachytherapy dosimetry study.
