Seed Implantation for Prostate Cancer

	X-ray view showing position of radioactive seeds within the prostate region.

21st Century Oncology is actively involved in radioactive seed implantation for prostate cancer, and is currently screening candidates. This procedure is performed in selected patients by a team of physicians and staff with nearly a decade of experience in prostate brachytherapy. The technique was first developed as a freehand procedure in the 1970s but was abandoned because of problems with erratic seed placement. Starting in 1983, with the improved accuracy of seed placement based on use of the transrectal ultrasound probe, a resurgence in prostate implantation occurred. This landmark change paved the way for the immense popularity that this technique enjoys today.

There are several key advantages to prostate brachytherapy:

• It is a convenient outpatient procedure. The patient generally can resume normal daily activities quickly.
• Radioactive seeds are inserted directly into the prostate, minimizing radiation exposure to surrounding tissues while permitting an escalation of the dose concentrated in the area of the prostate cancer.
• It can be done alone or in conjunction with Three-Dimensional Conformal External Beam Radiotherapy.
• 10-year results show that the vast majority of patients remain disease-free, making it an attractive alternative to both radical surgery and full-course external beam radiotherapy.
• Incontinence of urine occurs in only a tiny subset of patients, and impotence rates are less than with the other curative therapies.

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.

Logistics of the procedure

Once brachytherapy has been chosen, several things must occur. The prostate is measured for size using a transrectal ultrasound probe. This enables the radiation oncologist to order the appropriate number of seeds of whichever isotope has been selected. Depending upon the initial size of the prostate gland, prostate size reduction may be initiated with hormonal therapy before the final prostate measurement can be made prior to implantation. Prostates greater than 60 cubic centimeters in volume are often targeted for size reduction to make the implant feasible. This is accomplished by administering Lupron or Zolodex injections along with Casodex or Eulexin pills. The prostate is scanned again to confirm that it has fallen into the size category that can be implanted.

Once the prostate size has been accurately measured using the ultrasound probe, each patient undergoes a set of preoperative tests which includes blood work analysis, chest x-ray, EKG, and a physical examination. A bowel cleansing schedule is given to the patient to be followed at home the night before the procedure so that the rectum is free of stool, which can interfere with the ultrasound probe.

The prostate brachytherapy procedure

The implant is done on an outpatient basis, meaning that there is no overnight hospital stay. It is commonly fully covered by insurance. The work is done in a specially equipped operating room over 60-90 minutes. The radiation oncologist and urologist are both present for the case, and work as a team. Our technique offers the advantage of a computer-generated seed distribution that is created as the case occurs. This eliminates the potential for mismatching the prostate with a seed distribution plan that has been drawn up days or weeks ahead of time, as is commonly practiced at other centers.

The implantation of radioactive seeds into the prostate is generally done while the patient is asleep under general anesthesia. There are exceptions, depending upon individual medical circumstances. During the case, seed placement is guided by live images from the ultrasound probe, which is located in the rectum. Fifty to 150 seeds are inserted using 20-40 needles. This varies with the size and shape of the prostate, and whether the patient has had any previous Three-Dimensional Conformal External Beam Radiotherapy. The whole prostate is targeted since it impossible to pick out which parts are contaminated by cancer based on just a few biopsies. No imaging studies exist yet which can “see” the cancer in the prostate.

Once the seeds have been inserted, the urethra and bladder are carefully checked by the urologist. A drainage catheter is then inserted into the bladder and kept in overnight to ensure good urine flow even if there is swelling within the prostate. This catheter is removed the next day. Each patient is discharged with a set of instructions and prescriptions, as needed.

Postimplant procedure

One week following the implant procedure, the patient is asked to return for x-ray confirmation of the seed placement. One month after the procedure, a CT scan is performed. This is used by our physics staff for generating radiation measurements in the prostate based on seed location. A PSA blood test and rectal examination are checked when the patient returns for a check-up every six months.

Radiation safety

Although the seeds used to implant the prostate are radioactive, their energy is very low. Only negligible amounts are emitted from the patient’s body. This is usually not enough to be considered a health risk to others. Nevertheless, we adhere to the recommendation that the patient avoid close contact with children and pregnant women for two months. Iodine-125 seeds decay, or lose their energy, at a rate of 50% every 60 days. After 10 months, their radioactivity is nearly exhausted. Palladium-103 seeds decay much quicker, losing half their energy every 17 days. They are nearly inert after only 3 months. There is no need to remove the spent seeds, as they do not pose a hazard for the patient. They remain in place forever.

Side effects

Initially, there can be a tinge of blood or blood clots in the urine. This clears up quickly. A brief period of constipation may be related to the effects of the anesthesia. The puncture points from the needles used to insert the seeds can make the crotch and scrotum appear bruised due to minor leakage and shifting of blood in the tissues. Frequent urination and the sensation of urinary urgency are common following removal of the catheter. These dissipate over days to weeks. Sometimes there is weakening of the urinary stream, and there may be burning on urination. The rates of impotence, or loss of the ability to achieve an erection sufficient for sexual intercourse, are the lowest of any of the curative treatment options. This tends to vary with a patient’s age, health status, and sexual performance history.

Cure rates

The data extending out to 10-12 years show a cure rate that is as good or better than radical prostatectomy or external beam radiotherapy. The PSA level following an implant should eventually fall into a range less than 0.5-1.0 to be considered cured. Patients must be educated on each treatment option in order to make an informed decision.

How to contact us

The patient may be referred directly by the urologist, or call for an appointment at one of our locations.

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