PROSTATE SEED IMPLANTS
As a result of the widespread use of PSA testing, most patients with cancer are now diagnosed when prostate cancer is in an early stage. The three most common potentially curative treatment options offered to patients are radical prostatectomy, external beam radiotherapy (either conventional or high dose 3D conformal radiotherapy), and prostate seed implant therapy. As a result of the very high success rates and very low rates of undesirable side effects (e.g. erectile dysfunction, urinary incontinence, etc.), prostate brachytherapy, also known as prostate seed implantation, has become one of the most popular treatment options in the United States for early stage prostate cancer.
The modern era of prostate seed implantation began in the late 1980's in the United States. With the earlier techniques, the radioactive seeds were placed into the prostate using a freehand technique in which the seeds were "blindly placed" into the prostate. In contrast, the modern technique utilized a newly developed imaging technique in which an ultrasound probe was inserted into the rectum, making it possible to visualize the prostate in real time on a TV monitor. Ultrasound imaging and/or fluoroscopic imaging then observe the seed deposition into the prostate. Furthermore, no real surgery is involved and no incisions are made. The needles are first placed into an external grid which accurately guides the placement of the needles into the perineum and then into the prostate into the exact location utilizing real time ultrasound imaging. As this technique has evolved and technically improved, it has revolutionized the treatment of prostate cancer.
Prostate seed implants in the modern era were initially viewed with a high degree of skepticism because of the disappointing results of the earlier techniques in the 1960s and 1970s. However, in the 1980s and 1990s, many thousands of patients were successfully treated for prostate cancer with transperineal, transrectal, ultrasound-guided prostate seed implants. The move from skepticism to acceptance of the procedure by the medical community has been a result of the excellent intermediate and long-term results that have been reported in numerous highly respected medical journals in the late 1990s.
As this procedure has gained more widespread acceptance by the medical community, one of the major benefits has been the increase in cooperation and teamwork by the Urologist, Radiation Oncologists, and other members of the seed implant team. As a result, patients are inherently receiving both the surgical perspective by the Urologist and the radiotherapy perspective by the Radiation Oncologist. Thus, patients are becoming more educated about what treatment options they really have, resulting in the ability to make more educated and informed decisions about their chosen form of therapy.
FREQUENTLY ASKED QUESTIONS
Q. Who should be tested for prostate cancer and when?
A. The latest recommendation is that all men should be offered PSA testing on a yearly basis beginning at age 50. Individuals with a family history of prostate cancer and African Americans are considered to be at a high risk of developing prostate cancer and should be offered yearly PSA tests at age 40.
Q. Where is the prostate gland located?
A. The prostate gland is an organ that is approximately the size of a walnut, although the size is quite variable, that is located just below the urinary bladder and just in front of the rectum. The urethra, the structure that drains urine from the urinary bladder, is anatomically situated first within the prostate and then the penis. The opening at the penis is called the urethral meatus.
Q. What is the function of the prostate?
A. The prostate functions to produce a fluid that acts as the carrier of the sperm in the ejaculate. Approximately 95% of the volume of the ejaculate is produced by the prostate gland. This prostatic fluid serves a variety of useful functions during the process of conception.
Q. What is prostate cancer?
A. Cancer is an abnormal growth of cells that were derived from normal cells in the body. Unlike their normal cell counterpart, they do not experience the same checks and balances in the cell population of that organ or tissue type. This results in abnormal tumors or growths within the normal organs or tissues. When cells of the lining of the prostate gland become cancerous they are called adenocarcinoma of the prostate gland, which is commonly referred to as prostate cancer.
Q. Are all areas of the prostate gland at equal risk of becoming cancerous?
A. No, the prostate gland is a complex structure made up of approximately five unique areas. The area called the peripheral zone which is closest to the rectum is the area of the prostate in which most prostate cancer originates. This is because this area of the prostate has the greatest number of glands, and adenocarcinoma which is the most common form of prostate cancer is the type of cancer that originates in the cells lining the glands of the prostate. The second most commonly affected area is called the transitional zone, and this is the area of the prostate that surrounds the upper half of the urethra. It also has a significant number of glands within it (although much less than the peripheral zone) and adenocarcinoma is once again the most common type of cancer in this area of the prostate. Cancers of the transitional zone can sometimes result in symptoms of decreased caliber of the urinary stream, a weak urinary stream, and other symptoms of obstruction of the outflow of urine from the bladder. Your physician will use this information to plan your prostate seed implant.
Q. How long ago did doctors start performing prostate seed implants as treatment for prostate cancer?
A. In the early 1980's D. Holm (in Denmark) developed the first transrectal ultrasound guided transperineal prostate seed implants (TPPI). Physicians from the USA then learned this technique and began performing TPPI in the USA in the late 1980's. The procedure has really undergone major technical innovations in the last five years.
Q. How does the implant treat the cancer?
A. If you think about the way that the waves extend out concentrically from a pebble tossed in a pond, then you can imagine how the gamma rays extend out from each implant seed.
The concept behind a prostate implant is to strategically place the implant seeds such that the wave of each seed interacts with the wave of every other seed in a manner that gives the optimal dose of radiation to the prostate cancer while minimizing the radiation dose to the normal body tissues and organs.
Q. How does the radiation kill the cancer cells?
A. The radiation kills the cancer cells by causing damage to the genetic material (DNA) of the cancer cell. The cell is still physiologically viable and if biopsied would appear alive when viewed with a microscope. However, when this injured cell attempts to reproduce by the process called mitosis, it self-destructs, dies, and is eliminated by the normal body mechanism that eliminated dead cells. The idea is to give a high enough radiation dose to kill every last cancer cell.
Q. Are the normal tissue and organ cells also killed?
A. Yes, the normal cells of the tissues and organs that receive the radiation dose from the prostate seed implant are also injured. Some of the normal cells can repair the damage while others will die in a manner similar to that described above. However, one fortunately has many more normal cells than cancer cells in the area treated, and it is by this mechanism that every last cancer cell can be killed while sparing enough normal cells for the normal body tissues and organs to recover. It is the damage to the normal body tissues and organs that causes the side effects of the treatment.
Q. How is it that prostate seed implants cause less damage to the normal body tissues such as the rectum and bladder than external beam radiation therapy?
A. Iodine-125 implant seeds emit a very low energy gamma ray, which only travels for a very short distance. Thus, if the implant seeds are strategically placed, it is possible to minimize the damage to the normal body tissues such as the rectum, bladder, urethra, and erectile mechanism.
Q. When will the commonly observed side effects of prostate seed implant therapy occur?
A. Some of the side effects from radiation therapy (either external beam radiotherapy or prostate seed implant therapy) occur within days or weeks of the treatment and are called the acute side effects. Other side effects don't begin for six or more months after the treatment and are called the late side effects?
Q. Will there be a lot of pain after seed implant therapy?
A. No, most people are comfortable after the procedure and usually an over-the-counter preparation such as acetaminophen or ibuprofen will be all you'll need to take to be comfortable.
Q. What sort of urinary side effects can occur after seed implant therapy?
A. Most of the urinary side effects after the prostate seed implant occur and are a minor problem for the first few months after the seed implant. Other potential problems don't usually occur until six months or longer after the prostate seed implant. Some of the acute side effects of seed implant therapy are due to the swelling and bleeding within the prostate as a result of the trauma of the needle and seed placement that occurs during the operation. Other acute side effects are due to the radiation injury to the normal body tissues. This swelling narrows the urinary tract and often results in the urinary stream being weak, urinary dribbling, stopping and starting of the urinary stream, having to push or strain to begin urination. The acute side effects of the radiation are manifested primarily as increased urinary urgency and a burning or stinging sensation with urination, kind of like that with a bladder infection. Your physician will likely prescribe a variety of medications to help minimize the discomfort from the above noted symptoms. Sometimes the bladder becomes severely obstructed by the swelling and a Foley catheter must be placed back in the bladder for a few days, or on occasion a few weeks. If it appears that this will be a problem for a few months the patient will either be taught to catheterize himself or a suprapubic catheter will be placed. The main possible long-term side effects are chronic bladder outlet obstruction, urethral ulceration, and urethral necrosis with resultant pelvic pain; very rarely, urinary incontinence; and, extremely rarely, formation of a track between the rectum and urethra (called a fistula) with leakage of urine from the rectum.
Q. What sort of rectal side effects can occur after seed implant therapy?
A. In general, there are very few rectal side effects that occur after prostate seed implants. However, sometimes side effects do occur. Once again, some side effects occur shortly after the implant while others may not occur until many months later. The most common side effects during the first few months after the implant are an increased urgency of bowel movements; slight burning sensation of the rectum during bowel movements (kind of like hemorrhoid type of discomfort); and, rarely, some leakage of brown mucous type material with the passage of rectal gas (flatus). The main long-term problem is formation of a painful rectal ulcer if an implant seed is placed too close to the rectal wall or even into the muscle of the rectal wall. Some patients will have rectal bleeding similar to that which occurs after external beam radiotherapy. Extremely rarely, there can be a formation of a track between the rectum and urethra (called a fistula) with leakage of urine from the rectum.
Q. What is the risk of the seed implant therapy affecting your ability to have adequate enough erections for satisfactory sexual intercourse?
A. If you already have erectile dysfunction and are either not able to have erections or have partial erections that are not sufficient for intercourse you will more likely than not have erectile dysfunction after the prostate seed implant. If your erections are barely rigid enough for intercourse, or if they don't sustain adequately, you will have a very high risk of erectile dysfunction after the prostate seed implant therapy. There are possible treatment options for erectile dysfunction that you may whish to pursue. If you have reasonably good erectile function prior to the prostate seed implant, you will have about a 60% to 80% likelihood of having adequate erections after the prostate seed implant. Nearly all the treatment options will work well for those whose erections were good prior to prostate seed implant but are impaired afterwards.
Q. Is it safe to be around other individuals or sleep with your partner after the prostate seed implant?
A. Since the radiation from the iodine-125 is so weak, very little radiation leaves your body and you are not a radiation risk to those around you. From a radiation safely perspective, you may sleep in the same bed with your partner. Sexual intercourse may be resumed within the first few weeks after the seed implant. There is a remote risk of ejaculating a seed and you should wear a condom for the first couple of times you have intercourse. It is common practice to avoid close contact with children and pregnant women for two to four months after an iodine-125 prostate seed implant.
QUESTIONS AND ANSWERS ABOUT IODINE-125 SEEDS
Q. What are Prostate Implant Seeds?
A. The medical device commonly referred to as seeds are really individual small radioactive sources. They are 4.5 mm (3/16 in.) in length and 0.8 mm (1/32 in.) in diameter. Each one consists of an outer titanium shell. The radioactive iodine-125 is then inserted into the seed, along with radiopaque markers (so that the individual seeds can be seen on x-ray films and with fluoroscopy), and microscopically laser-welded shut to completely retain the radioactive material within the device.
Q. Where does the Iodine-125 come from?
A. While iodine-125 is a naturally occurring radioactive element, the iodine-125 used in the implant seeds is made in a nuclear reactor.
Q. What kind of radiation do the implant seeds give off?
A. Iodine-125 is a radioisotope that emits both photons called gamma rays (which are like x-rays) and low energy beta particles (which are like electrons). However, the titanium shell of the seed filters out nearly all the emitted radiation except that which is desirable for the treatment of cancer. What the seed ultimately emits is predominantly a 28-kiloelectron volt gamma ray, which is a very weak type of x-ray like photon. In fact, it is significantly weaker than the x-rays used to produce a chest x-ray, for instance.
Q. What is the advantage of Iodine-125 seeds?
A. To date, there is no clear answer as to whether any one type of radioactive seed is better than another. The two most commonly used radioactive seeds are iodine-125 and palladium-103 seeds. While many physicians have their opinion as to which type of seed is best, it is important to recognize that this is, in reality, an unanswered medical question. However, there is basic science information that suggests that as a result of the physics properties of iodine-125, it may be easier for physicians to perform an implant achieving the desired radiation dose.
Q. What is the potential benefit of using Iodine-125 seeds?
A. Since iodine-125 seeds emit a very weak gamma ray, it is possible to strategically place them in and around the prostate in a manner that minimizes the radiation dose to normal tissues and organs such as the urinary bladder, urethra, nerves and blood vessels that allow for erectile function, and rectum while optimizing the dose to the prostate cancer. As a result, the side effects of the treatment are minimized and cure rate of the cancer maximized.
QUESTIONS AND ANSWERS ABOUT THE SEED IMPLANT PROCEDURE
Q. What is the difference between "preplanned prostate implants" and "Real-Time planning prostate implants”?
A. The majority of physicians performing prostate seed implants in the United States do so using a preplanned procedure. Patients having a preplanned prostate seed implant procedure have a special ultrasound scan performed days to weeks before the actual seed implant is performed. Your Radiation Oncologist and Urologist then determine the areas of the prostate and surrounding structures that need to be treated, as well as those that need to be protected. The Radiation Physicist or Dosimetrist then enters this information into a very powerful treatment planning computer and a plan is formulated that optimizes the seed placement for your prostate. An order is then placed for the exact number of seeds needed for your prostate implant, as well as the precise radioactive strength of the seeds. The urologist and Radiation Oncologist then follow the preplan while in the operating room and perform the procedure as it was designed in the 3D computer. Of course the simulation is often slightly different during the operation than at the time of the preplanning ultrasound study, and your physicians will make the necessary intraoperative modifications.
The other commonly used prostate implant technique is called a real-time prostate implant. Based on the volume of your prostate, a given number of seeds of a given radioactive strength are ordered based on a nomogram (a reference table of sorts) or preplan. In the operating room the Urologist and Radiation Oncologist then measure the prostate gland to determine where the seeds will be placed when the implant is performed. The Radiation Oncologists and the Urologist can actually visualized the seeds as they are implanted and modify the treatment plan as needed. This “Real-Time prostate planning” technique allows physicians to perform the highest quality implant which should yield the best possible result.
Q. What is the post-implant dosimetric evaluation?
A. Regardless of which technique your physicians use to perform your implant, you will very likely have an evaluation of your prostate seed implant performed the same day as your implant or within the month prior to your prostate seed implant. This often involves having certain radiological studies performed. Most commonly, pelvic x-rays from the front and side view are taken first. This provides a rather permanent record of your implant and assists in accurately accounting for all the seeds placed during the prostate seed implant procedure. However, one can only see the seed pattern in the pelvic area, and not the prostate itself. Very often a CT scan through the region of the prostate seed implant is obtained. This allows your physician to see the implant seeds, the prostate, and other surrounding organs and structures, as well as the actual location of the seeds within and around the prostate. This information can then be entered into the 3D treatment planning computer and your implant can be carefully evaluated to assure that the desired result was actually achieved.