Prostate Seed Implantation
Prostate seed implantation is a minimally invasive procedure for treating prostate cancer in which radioactive seeds are placed in the prostate gland to target cancer cells while maximizing the preservation of healthy tissue. This outpatient procedure requires general anesthesia and takes only a few hours. Most patients return to normal activities within two to three days. Our doctors are experts in treating prostate cancer patients using prostate seed implantation, having pioneered its use over a decade ago.
Initial radioactive seed implantation was performed via “free-hand” technique, using direct visualization of the prostate to guide the radiation oncologist with seed placement. However, the results of this preliminary approach was hampered by suspect dose distribution in the prostate.
In 1987, Dr. Blasko from Seattle described a reproducible system to implant radioactive Iodine seeds in the prostate. This Seattle system employs a rectal ultrasound probe to directly visualize the prostate and a plastic template placed on the patient’s perineum (region between the scrotum and the rectum). The template guides the placement of the needles which are loaded with radiactive seeds. This technique allows a reproducible,uniform dose distribution to the prostate.
The physicians of Princeton Radiation Oncology have been performing this procedure since 1997.
Prostate seed implantation is not for everyone. Treatment decisions are based on important prognostic factors:
- Gleason grade
- PSA level
Princeton Radiation Oncology physicians have adopted the Seattle group’s criteria for implant selection. An ideal candidate should have a PSA level <10, Gleason grade 6 or less, with non-palpable disease.
The size of the prostate is also an important factor. As a general rule, patients with prostate glands >60cc are at increased risk for pelvic arch obstruction and poor dose distribution. Androgen deprivation (hormone therapy) can be used to shrink large prostates for several months to allow an optimal seed implant.
Patients who previously have had a vigorous transrectal resection of the prostate (TURP) for benign prostatic hypertrophy may not be ideal candidates for this implant procedure. Higher rates of urinary complications have been reported for these subset of patients.
The first step in the process is an outpatient consultation with a radiation oncologist. The radiation oncologist will advise on the implant option based on the patient’s PSA, Gleason score, tumor stage, and other factors.
The second step is a planning transrectal ultrasound (TRUS). A transducer is placed in the rectum and images of the prostate gland are obtained in 5mm segments. Once the prostate is visualized, the radiation oncologist works with the radiation physicists to determine where the seeds should be placed. Through the use of a treatment planning computer, a series of “dose maps” called isodose curves are generated. The goal is to deliver a dose of 150-160 Gy to the prostate with Iodine (I-125) and approximately 120 Gy with Palladium seeds (Pd-103). The seeds are “peripherally loaded” to minimize the dose to the centrally located urethra. This will minimize the risk of urinary side effects.
The third step is the implant procedure. This is performed in the operating room under either general or spinal anesthesia. Under transrectal ultrasound guidance, the prostate is implanted through the perineum with needles loaded with radioactive seeds. Fluoroscopy confirms the seed placement into prostate. Immediately after the procedure, the patient is monitored for several hours. Typically, the patient is discharged to home on the same day.
The outcome of implantation is highly operator dependent. As such, it is important for the radiation oncologist to be experienced and proficient with this procedure. The physicians of Princeton Radiation Oncology are among the most experienced and have been instrumental in pioneering this treatment option.
The Northwest Tumor Institute have documented excellent 10 year follow up data. Their long-term outcome was comparable to external beam radiation therapy and surgery. Although 20 year data is not yet mature, prostate seed implant appears to be just as effective as surgery or external beam radiatherapy for early stage prostate cancers.
A common misconception among prospective patients is that prostate implantation has fewer side effects than external beam radiation therapy. This indeed is a misconception. Nearly all patients suffer from some urethritis. Urinary retention requiring a temporary catheter occurs in 5% of the patients.