|
|
Brachytherapy
Brachytherapy ("seed implantation") involves placement of radioactive sources ("seeds") directly into tissues harboring cancerous tumors. The word "brachytherapy" means "short therapy," indicating that the radiation is limited to short distances. Unlike external beam radiation therapy, where radiation energy must traverse normal tissues from outside the body to reach the cancerous organ, brachytherpy energy is emitted outward from each "seed," allowing a concentration of radiation energy in the diseased tissue. This strategy of delivering radiation can result in decreased toxicity and/or the ability to achieve higher radiation dosages ("dose escalation") than is possible with external beam radiation. The concept of dose escalation is particularly important, as multiple studies have shown that increased radiation dose results in an improved ability to cure prostate cancer (1-3).
Overview
Prostate brachytherapy is not a new concept; Alexander Graham Bell suggested the idea as far back as 1903. Louis Pasteur advocated inserting radium into the prostate in 1911. Over the years, various approaches were tried with limited success. In the 1960's and 1970's seeds were inserted into the prostate via an open incision on the lower abdomen. Unfortunately, all of these techniques ultimately failed due to both a poor understanding of the amount of radiation needed to control prostate tumors, as well as an inability to adequately visualize the prostate and the seeds during the implant. This inability to easily visualize the prostate, and to direct the seeds properly while the implant was occurring, resulted in a failure to optimally distribute the seeds and consequently inadequate coverage by the radiation.
Modern brachytherapy was developed by investigators in Europe and the United States in the mid-1980's. Modern seed implantation resulted from the emergence of two concepts: first, that the prostate can be well visualized in "real-time" in the operating room using ultrasound imaging via a probe placed in the patient's rectal cavity; second, that seeds could be accurately deposited in the prostate by introducing them using needles passed through a template grid positioned over the man's perineum (the area between the scrotum and the rectum). The use of trans-rectal ultrasound is important not only in accurately defining the shape and position of the prostate and adjacent structures, but also in guiding needle placement within the prostate. These advances, combined with an improved understanding of the proper number and strength of seeds needed, has led to a tremendous resurgence of prostate brachytherapy. It has been estimated that 1/3 to 1/2 of all men diagnosed with clinically localized prostate cancer undergo seed implantation.
Today, two types of seeds are in common use: Palladium-103, and Iodine-125. While these seeds differ in certain physical characteristics (palladium seeds deliver essentially all of their effective energy in two months, while iodine seeds take six months), there is no evidence that either is more effective in eradicating prostate cancer (4, 5). Both seed types deliver highly effective, dose-escalated radiation within a 5 mm. radius around the seed, but beyond this margin there is a rapid fall-off of delivered dose.
This allows seeds to be implanted adjacent to normal tissues such as the bladder, urethra, and rectum with an acceptable risk of side effects. Once the seeds have expended their energy they become essentially inert, and they never actually need to be removed from the patient. Because of the physical property of rapid dose fall-off, patients with implanted seeds pose no significant radiation danger to the general public. Casual contact with all members of the family may be maintained, although some minimal precautions are advised when very young children or pregnant women are in close proximity.
The Brachytherapy Procedure
All patients treated with prostate brachytherapy undergo a two step process. First, it is necessary to measure the precise size and shape of the prostate so that the proper number and strength of seeds can be determined for each patient. In most centers this "mapping" step is accomplished by a trans-rectal ultrasound procedure. However, due to the discomfort and inconvenience of trans-rectal ultrasound, physicians at The Urology Center have pioneered an alternative approach to "mapping" the prostate which utilizes a non-invasive CT scan instead of the ultrasound (a minority of patients, for technical reasons relating to the particular size or shape of their prostate, may still require a preliminary ultrasound procedure). Once the patient's prostate anatomy has been defined, computer modeling is used to determine the optimal number, strength, and position of seeds specifically needed for that particular patient. This work is done in conjunction with radiation oncology physicians, as well as ancillary staff who are specially trained in medical physics.
The second step is the actual seed implantation session itself. The implant is performed as an outpatient procedure, generally one to two weeks following the initial "mapping" procedure described above. Patients undergo general anesthesia. They are positioned with their legs elevated in stirrups, so that physicians will have access to the perineal area. The ultrasound probe is placed in the rectal cavity and the template is affixed to the ultrasound probe. Needles, each loaded with from one to five or six seeds, are then passed through the template into the perineal skin and prostate under ultrasound guidance, and the seeds deposited. Most centers rely solely upon the preliminary "mapping" procedure to determine the position of the needles and seeds for the implant session. However, it is becoming increasingly recognized that an intra-operative reassessment of the precise shape, position, and size of the patient's prostate-with adjustment and optimization of the planned seed positions-is desirable to insure a more accurate deployment of the seeds (6-10). Urologists and radiation oncologists at The Urology Center have been on the leading edge of developing these techniques of so-called "intra-operative planning."
Prostate implants are performed with both the urologist and radiation oncologist working as a team, and usually involves placement of 15 to 25 needles and anywhere from 60 to 100 or more seeds. At the conclusion of the implant, which takes about sixty to ninety minutes to perform, a catheter is placed in the bladder and the patient is taken to the recovery room. Before discharge from the facility, a confirmatory CT scan is performed and subsequently analyzed to be sure that the seeds were placed as planned. In the very rare instance that the seed distribution is felt to be problematic, additional seeds could be placed at a later date. Many patients are discharged with a urethral catheter in place overnight, with instructions to remove the catheter on their own the next morning. This allows time for a reduction of prostate swelling that may occur as a result of the procedure. Patients routinely find this short-term catheter and its removal easy to manage.
Prostate brachytherapy is a highly effective treatment for localized prostate cancer. Several series have now reported overall cancer-free survival rates of 70-87% with 9 to 15 years of follow-up (11-16). Cancer-free survival rates following other prostate cancer treatments such as surgical removal (17, 18) and conformal external beam radiation (19) are essentially indistinguishable from those of brachytherapy at this time. Regardless of the method of cancer treatment, disease-free survival is assessed by measuring post-treatment PSA levels. Since the PSA entered clinical use in the late 1980's, about the same time that modern brachytherapy began to be practiced, there is essentially the same duration of follow-up available for seed implantation as the other treatment methods.
Unfortunately, all patients do not enjoy the same chance of cure, whether treated with brachytherapy, surgery, or external radiation. The ability to cure patients with prostate cancer is highly dependent on the size and aggressiveness of the cancer at the time of diagnosis. Patients with larger, more aggressive tumors are at risk for occult involvement of the soft tissues adjacent to the prostate ("extra-capsular disease"). Since such disease extension is microscopic, it is difficult or impossible to detect its presence at the time of diagnosis. However, a patient's probability of extra-capsular involvement may be estimated by taking several factors into consideration, including the clinical stage as determined by the digital rectal exam, PSA level, Gleason score (a measure of cancer aggressiveness), the amount of tissue involved with cancer in the original prostate biopsies, and other factors. Whether patients have surgery or radiation for prostate cancer, patients who are at low risk for extra-prostatic disease have cure rates in the 80-90% range, whereas less fortunate patients at high risk have cure rates that drop to the 40-60% range.
When patients are judged to be at significant risk for extra-capsular disease, combinations of treatment modalities may be recommended. Approximately 20% of patients will be advised to undergo external beam radiation combined with seed implantation, as this treatment strategy can cover a wider area with dose-escalated radiation. Other patients may be advised to receive hormone treatment along with external radiation or seed implantation, since hormone therapy may result in increased effectiveness of radiation in some circumstances. Similarly, patients treated via surgical removal of the prostate may require the addition of external radiation if the cancer extends beyond the excision margin. These treatment judgments are complex and require highly individualized decision-making, which should occur as a result of careful consultation between each patient and their physician.
Risks and Complications
Side effects of all methods of treatment for localized prostate cancer may involve three areas of body function intimately associated with the prostate anatomically: urinary function, since the bladder is adjacent to and the urethra traverses the prostate; sexual function, since the nerves that control erections run along the surface of the prostate; and rectal function, since the prostate is so closely approximated to the rectal surface.
The primary short term side effect of prostate brachytherapy is urinary difficulty due to prostate swelling. Approximately 10% of patients require a urinary catheter for a period beyond the overnight time-frame, due to a poor ability to urinate (20). Although this degree of voiding difficulty occurs in only a relatively low percentage of cases, most patients will experience some lesser degree of temporary urinary alteration, such as frequency of urination, decrease in the urinary stream, or urinary discomfort. These symptoms typically resolve within several weeks to months of treatment. Long term voiding difficulty is relatively uncommon, affecting only about 6% of men treated (21). Patients with large prostates and/or significant urinary symptoms at baseline (prior to treatment) are at increased risk for urinary side effects, and consequently may not be appropriate candidates for prostate brachytherapy. Urinary incontinence (leakage) is considered rare after brachytherapy, and generally is not a concern unless the patient has a history of prior prostate surgery. This is in contrast to surgical removal of the prostate, which is associated with about a 10% risk of some degree of long-term urinary leakage (22).
Sexual side effects are obviously of concern for many patients and their partners. All forms of prostate cancer treatment can result in decreased or absent erections. Erectile dysfunction develops in 25-40% of well-functioning men within five years of prostate brachytherapy (22-24). Loss of ejaculate fluid occurs in up to 50% of men (25). By way of comparison, surgical removal of the prostate results in immediate loss of erections in about 50% of men, including those who undergo a "nerve sparing" operation (26). Surgical removal always results in complete loss of ejaculatory fluid. Patients probably have a somewhat better chance of responding to simple oral medications for erectile dysfunction after brachytherapy than surgery (27). In cases where external beam radiation or hormone therapy is added to seed implantation due to the extent of the cancer, the chance of ultimately developing erectile dysfunction is probably higher (22,23,28).
Rectal side effects of prostate brachytherapy are of less significance to most patients than the urinary and sexual issues discussed above. Although seed implantation delivers radiation very precisely, the proximity of the prostate to the rectum necessarily results in some radiation exposure to the bowel wall. Some patients will therefore experience more frequent bowel movements, while others may actually become constipated, shortly after implantation. These effects are generally quite transient, lasting only a few weeks (29).
Proctitis, a delayed inflammatory reaction of the rectum due to radiation, is a more troublesome side effect that may occur one to three years after radiation exposure. This usually manifests as mild rectal bleeding; serious bleeding is rare, occurring in only 0.5 to 1% of implant patients (30, 31). The incidence of proctitis is somewhat higher when external beam radiation is combined with seed implantation (31); it is significantly higher (8-16%) in patients who choose to undergo dose-escalated forms of external beam radiation (such as "IMRT") as their sole treatment, since all forms of external radiation result in more rectal exposure than seed implantation (32). Surgery to remove the prostate does not generally lead to rectal side effects, unless it is necessary to add external radiation to the treatment program in those patients with more extensive cancers.
Seriousness of purpose, combined with the latest in prostate brachytherapy techniques, facilities, and equipment, are the hallmarks of The Urology Center's prostate brachytherapy program. We have an extremely active and successful implant program, treating about 225 patients per year. We perform more implants than any other facility in the Cincinnati and Tri-State area. Our physicians are known both regionally and nationally for their expertise in brachytherapy. They have lectured and participated in educational panels across the country describing the latest developments in the field. The Urology Center, as a recognized leader in prostate brachytherapy, also provides a regularly scheduled teaching course in the most current techniques in brachytherapy, attended by urologists and radiation oncologists from across the United States.
References
- Zelefsky, Int. J. Radiation Biology Physics, 1998
- Hanks, Int. J. Radiation Biology Physics, 2002
- Zelefsky, Int. J. Radiation Biology Physics, 2002
- Potters, Brachytherapy, 2003
- Cha, Int. J. Radiation Biology Physics, 1999
- Yamada, Am. J. Clin. Oncol., 2003
- Zelefsky, Int. J. Radiation Biology Physics, 2000
- Beyer, Int. J. Radiation Biology Physics, 2000
- Wilkinson, Int. J. Radiation Biology Physics, 2000
- Kirsh, Brachytherapy (supp.), 2003
- Ragde, Cancer, 2001
- Grimm, Int. J. Radiation Biology Physics, 2001
- Blasco, Int. J. Radiation Biology Physics, 2000
- Datoli, Cancer, 2003
- Sylvester, ASCO, 2004
- Potters, Int. J. Radiation Biology Physics (supp.), 2004
- Kupelian, Int. J. Radiation Biology Physics, 2004
- Vicini, Cancer, 2002
- Zelefsky, Int. J. Radiation Biology Physics (supp.), 2003
- Crook, Int. J. Radiation Biology Physics, 2002
- SEER, JAMA, 2000
- Potters, Int. J. Radiation Biology Physics, 2001
- Merrick, Int. J. Radiation Biology Physics, 2002
- Stock, J. Urology, 2001
- Incrocci, Int. J. Radiation Biology Physics, 2002
- SEER, JAMA, 2000
- Zippe, Urology, 2000
- Kassabian, Int. J. Radiation Biology Physics (supp.), 2004
- Ghaly, Int. J. Radiation Biology Physics, 2003
- Gelbum, Int. J. Radiation Biology Physics, 2000
- Kang, Int. J. Radiation Biology Physics, 2002
- Skwarchuk, Int. J. Radiation Biology Physics, 2000
|
|
|
 |
|
|
| Copyright © 2012 - The Urology Group - All rights reserved |
|
