Radiation Therapy
Radiation Therapy
Radiation therapy attempts to destroy the cancer cells within the prostate without actually removing the gland. The limiting factor in treating cancers with radiation energy is collateral damage. Radiation does not distinguish normal cells from cancer cells. Thus, all cells within the treatment area will be killed. Unfortunately, this factor limits the use of radiation because of the proximity of important normal structures around the prostate gland which will be effected by the energy. Radiation therapy is continually improving in it’s ability to target primarily the prostate gland while limiting the damage to the surrounding structures. The closest surrounding structures effected include the anterior wall of the rectum, the base of the bladder, the urinary sphincter and the nerves running along the sides of the prostate which are essential for the normal maintenance of male erectile functioning.
Radiation therapy to the prostate gland can be accomplished by either external beams or the implantation of radioactive seeds directly into the prostate gland. Today, it is generally recommended that all patients who undergo any form of radiation treatment for prostate cancer undergo hormone ablation therapy prior to radiation and continuing after for up to one year. Studies have suggested improved effectiveness of the radiation therapy after hormone therapy.
It should also be pointed out that any form of radiation therapy to the prostate generally precludes the surgical removal of the prostate at a later date. The complications of surgical removal of the prostate after radiation therapy are significant and frequent. However, external beam radiation therapy can be an effective adjunct after surgical removal of the prostate in patients with locally extensive disease.
External Beam Radiation Therapy
External beam radiation therapy has been used to treat prostate cancer for well over 50 years. Radiation is delivered to the prostate gland in beams from an external source. The patient would lie on a table below the radiation machine (similar to getting a routine chest x-ray). Beams of radiation are targeted at the prostate gland. In order to limit damage to the surrounding structures, multiple approaches are used to aim at the prostate. This technique of only delivering a fraction of the total radiation does in one projection, limits the dosage received by the surrounding structures. External beam radiation is accomplished in multiple small doses usually given 5 days a week for approximately 6-7 weeks. Each treatment visit usually lasts about 15-20 minutes. External beam radiation therapy is advantageous in patients who must remain anticoagulated or have serious other medical contraindications to anesthesia or surgery.
Interstitial Radioactive Seed Implantation (Brachytherapy)
Brachytherapy utilizes tiny radioactive seeds which are directly implanted into the prostate gland thru needles placed into the skin of the perineum (the area between the rectum and scrotum). Radioactive seeds have a unique property in that the radiation energy will only affect the tissue immediately surrounding the seed. This property is helpful in that it limits damage to important non-cancerous tissue. However, it also requires careful placement of seeds throughout the entire prostate if all of the cancerous cells are to be killed. Seed implantation for prostate cancer was first tried in the late sixties and early seventies with poor success because of inadequate radiation dosage to eradicate all of the cancer. Today, seed implantation is much improved because of the ability to place the seeds into the prostate under direct visual guidance using transrectal ultrasound, which has only been available since the mid 1980s. However, by the very nature of the procedure, certain contraindications to seed implantation have evolved with increasing experience. Contraindications to seed implantation include a Gleason score of 7 or above, a PSA greater than 10, palpable tumor on digital rectal exam, patient anticoagulation, a large prostate (volume > 40 cc) or a patient with severe obstructive voiding symptoms prior to implantation.
The potential benefits of seed implantation include: It is a single outpatient procedure and data suggest better sparing of erectile function than external beam therapy.
The potential disadvantages of seed implantation over external beam radiation include: Seed implantation requires at least one and often two general anesthetics. Periods of urinary retention can occur frequently requiring prolonged intervals with a urinary catheter to drain the bladder. Occasional patients will experience various degrees of pain or discomfort in the area of the prostate and rectum following seed implantation. Studies suggest that seed implantation is less effective than external beam radiation therapy in patients with high grade or microscopic locally extensive prostate cancer.