Radiation therapy uses high-energy rays or particles to kill cancer cells. Radiation is sometimes used as the initial treatment for low-grade cancer that is still confined within the prostate gland or that has only spread to nearby tissue. Cure rates for men with these types of cancers are much like those for men getting radical prostatectomy. Radiation is also sometimes used if the cancer is not completely removed or comes back (recurs) in the area of the prostate after surgery. If the disease is more advanced, radiation may be used to reduce the size of the tumor and to provide relief from present and possible future symptoms.
Two main types of radiation therapy are used: external beam radiation and brachytherapy (internal radiation). Both appear to be good methods of treating prostate cancer, although there is more long-term information about the results of treatment with external beam radiation.
External beam radiation therapy (EBRT)
In EBRT the radiation is focused on the prostate gland from a source outside your body. It is much like getting an x-ray but for a longer time. Before treatments start, imaging studies such as MRIs, CT scans, or plain x-rays of the pelvis are done to find the exact location of your prostate gland. The radiation team may then make some ink marks on your skin that they will use later as a guide to focus the radiation in the right area. You will usually be treated 5 days per week in an outpatient center over a period of 7 to 9 weeks. Each treatment lasts only a few minutes and is painless.
Aside from being used as a treatment for early stage cancer, external beam radiation can also be used to help relieve bone pain when the cancer has spread to a specific area of bone.
Standard (conventional) EBRT is used much less often than in the past. Newer techniques allow doctors to give higher doses of radiation to the prostate gland while reducing the radiation exposure to nearby healthy tissues. These techniques have fewer side effects than standard EBRT. They may also have a better chance of curing the cancer, but this has not yet been proven in studies.
Three-dimensional conformal radiation therapy (3D-CRT): 3D-CRT uses special computers to precisely map the location of your prostate. You will likely be fitted with a plastic mold resembling a body cast to keep you in the same position so that the radiation can be aimed more accurately. Radiation beams are then shaped and aimed at the prostate from several directions, which makes it less likely to damage normal tissues.
This method seems to be at least as effective as standard radiation therapy with lower side effects. Many doctors now recommend using it when it is available. In theory, by aiming the radiation more accurately, doctors can reduce radiation damage to tissues near the prostate and cure more cancers by increasing the radiation dose to the prostate. Long-term study results are still needed to confirm this.
Intensity modulated radiation therapy (IMRT): IMRT is an advanced form of 3D therapy. It uses a computer-driven machine that actually moves around the patient as it delivers radiation. In addition to shaping the beams and aiming them at the prostate from several angles, the intensity (strength) of the beams can be adjusted to minimize the dose reaching the most sensitive normal tissues. This allows doctors to deliver an even higher dose to the cancer areas. Many major hospitals and cancer centers are now able to provide IMRT. The RapidArc™ is a form of IMRT that allows each treatment to be given over just a few minutes. It is more convenient for the patient, but is similar to regular IMRT in terms of effectiveness
Conformal proton beam radiation therapy: Proton beam therapy is related to 3D-CRT and uses a similar approach. But instead of using x-rays, this technique focuses proton beams on the cancer. Protons are positive parts of atoms. Unlike x-rays, which release energy both before and after they hit their target, protons cause little damage to tissues they pass through and then release their energy after traveling a certain distance. This means that proton beam radiation may be able to deliver more radiation to the prostate and do less damage to nearby normal tissues. Although early results are promising, studies are needed to see if proton beam therapy is better in the long-run than other types of external beam radiation. Right now, proton beam therapy is not widely available. The machines needed to make protons are expensive, and there are only a handful of them in use in the United States. Proton beam radiation may not be covered by all insurance companies at this time.
Stereotactic radiosurgery: This method is a form of IMRT that is most commonly used to treat cancer that spreads to the brain. It involves holding the head in a metal frame or cage to prevent any movement, while the machine delivers radiation precisely to the tumor. When only a single treatment is given, it is called stereotactic radiosurgery, but when many treatments are given it is called stereotactic radiotherapy. This treatment often goes by the names of the machines used to give it, such as Gamma Knife™, Novalis Tx™, and CyberKnife™.
Possible side effects of external beam radiation therapy: The numbers used to describe the possible side effects below relate to standard external radiation therapy, which is now used much less often than in the past. The risks of the newer treatment methods described above are likely to be lower.
Bowel problems: During and after treatment with external beam radiation therapy, you may have diarrhea, sometimes with blood in the stool, rectal leakage, and an irritated large intestine. Most of these problems go away over time, but in rare cases normal bowel function does not return after treatment ends. In the past, about 10% to 20% of men reported bowel problems after external beam radiation therapy, but the newer conformal radiation techniques may be less likely to cause these problems.
Bladder problems: You might find yourself needing to urinate more often, having a burning sensation while you urinate, and finding blood in your urine. Bladder problems usually improve over time, but in some patients they never go away. About 1 patient out of 3 continues to have problems with needing to urinate more often.
Urinary incontinence: This side effect is less common than after surgery overall, but the chance of incontinence goes up each year for several years after treatment.
Impotence: After a few years, the impotence rate after radiation is about the same as that of surgery. It usually does not occur right after radiation therapy but slowly develops over a year or more. This is different from surgery, where impotence occurs immediately and may improve over time. In older studies, about 3 out of 4 men were impotent within 5 years of having external beam radiation therapy (some of these men had erection problems before treatment). In men who had normal erections before treatment, about half became impotent at 5 years. It's not clear if these numbers will apply to newer forms of radiation as well. As with surgery, the older you are, the more likely it is you will become impotent. Impotence may be helped by treatments such as those listed in the section above, including erectile dysfunction medicines.
Feeling tired: Radiation therapy may also cause fatigue that may not disappear until a few months after treatment stops.
Lymphedema: Fluid buildup in the legs or genitals (described in the surgery section of this document) is possible if the lymph nodes receive radiation.
Urethral Stricture: The tube that transmits urine from the bladder out of the body may, rarely, be scarred and narrowed by radiation, and require further treatments to open it up again.
Brachytherapy (internal radiation therapy)
Brachytherapy (also called seed implantation or interstitial radiation therapy) uses small radioactive pellets, or "seeds," each about the size of a grain of rice. These pellets are placed directly into your prostate. Brachytherapy is generally used only in men with early stage prostate cancer that is relatively slow growing (such as low-grade tumors).
Its use may also be limited by other factors. For men who have had a transurethral resection of the prostate (TURP) or for those who already have urinary problems, the risk of urinary side effects may higher. Brachytherapy may not be as effective in men with large prostate glands because it may not be possible to place the seeds into all of the correct locations. Doctors are now looking at ways to get around this, such as giving men a short course of hormone therapy beforehand to shrink the prostate.
Imaging tests such as transrectal ultrasound, CT scans, or MRI help guide the placement of the radioactive pellets. Special computer programs calculate the exact dose of radiation needed. Without these, the cancer might get too little radiation or the normal tissues around it could get too much.
There are 2 types of prostate brachytherapy. Both are done in an operating room and require some type of anesthesia.
Permanent (low dose rate, or LDR) brachytherapy: In this approach, pellets (seeds) of radioactive material (such as iodine-125 or palladium-103) are placed inside thin needles, which are inserted through the skin in the area between the scrotum and anus (perineum) and into the prostate. The pellets are left in place as the needles are removed and give off low doses of radiation for weeks or months. Radiation from the seeds travels a very short distance, so the seeds can put out a very large amount of radiation to a very small area. This decreases the amount of damage done to the healthy tissues that are close to the prostate.
Usually, anywhere from 40 to 100 seeds are placed. Because they are so small, their presence causes little discomfort, and they are simply left in place after their radioactive material is used up. This type of radiation therapy requires spinal anesthesia (where the lower half of your body is numbed) or general anesthesia (where you are asleep) and may require 1 day in the hospital.
You may also receive external beam radiation along with brachytherapy, especially if there is a risk that your cancer has spread outside of the prostate (for example, if you have a high Gleason score).
Temporary (high dose rate, or HDR) brachytherapy: This is a newer technique. Hollow needles are placed through the perineum into the prostate. Soft nylon tubes (catheters) are placed in these needles. The needles are then removed but the catheters stay in place. Radioactive iridium-192 or cesium-137 is then placed in the catheters, usually for 5 to 15 minutes. Generally, about 3 brief treatments are given, and the radioactive substance is removed each time. The treatments are usually given over 2 days. After the last treatment the catheters are removed. For about a week following placement of the catheters, you may have some pain or swelling in the area between your scrotum and rectum, and your urine may be reddish-brown.
These treatments are usually combined with external beam radiation given at a lower dose than if used by itself. The total dose of radiation is computed so that it is high enough to kill all the cancer cells. The advantage of this approach is that most of the radiation is concentrated in the prostate gland itself, sparing the urethra and the tissues around the prostate such as the nerves, bladder, and rectum.
Possible risks and side effects of brachytherapy: If you receive permanent brachytherapy seeds, they will give off small amounts of radiation for several weeks. Even though the radiation doesn't travel far, your doctor may advise you to stay away from pregnant women and small children during this time. You may be asked to take other precautions as well, such as wearing a condom during sex.
There is also a small risk that some of the seeds may move (migrate). You may be asked to strain your urine for the first week or so to catch any seeds that might come out. Be sure to carefully follow any instructions your doctor gives you. There have also been reports of the seeds moving through the bloodstream to other parts of the body, such as the lungs. As far as doctors can tell, this doesn't seem to cause any ill effects and happens very rarely.
Like external beam radiation, brachytherapy can also cause impotence, urinary problems, and bowel problems.
Bowel problems: Significant long-term bowel problems (including burning and rectal pain and/or diarrhea) occur in less than 5% of patients.
Urinary problems: Severe urinary incontinence is not a common side effect. But frequent urination may persist in about 1 out of 3 patients who have brachytherapy. This is perhaps caused by irritation of the urethra, the tube that drains urine from the bladder. Rarely, this tube may actually close off (known as urethral stricture) and need to be opened with surgery.
Impotence: Problems with erections may be less likely to develop after brachytherapy than after other common forms of treatment, but this is unclear. Some studies have found rates of sexual dysfunction to be lower after brachytherapy, but other studies have found that the impotence rates were no lower than with external beam radiation or surgery. Again, the younger you are and the better your sexual function before treatment, the more likely you will be to regain function after treatment.
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