Radiation therapy for prostate cancer
Radiation therapy uses high-energy rays or particles to kill cancer cells. Radiation may be used:
Two main types of radiation therapy can be 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. (Another type of radiation therapy, in which a medicine containing radiation is injected into the body, is described in the section "Preventing and treating prostate cancer spread to the bone.")
External beam radiation therapy (EBRT)
In EBRT, beams of radiation are focused on the prostate gland from a machine outside the body. This type of radiation can be used to try to cure earlier stage cancers, or to help relieve symptoms such as bone pain if the cancer has spread to a specific area of bone.
To reduce the risk of side effects, doctors carefully figure out the exact dose of radiation needed and aim the beams as accurately as they can to hit the carefully outlined target. Before treatments start, imaging tests 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 a week in an outpatient center for 7 to 9 weeks. Each treatment is much like getting an x-ray. The radiation is stronger than that used for an x-ray, but the procedure is painless. Each treatment lasts only a few minutes, although the setup time — getting you into place for treatment — takes longer.
EBRT for prostate cancer is most often given using techniques that let doctors give higher doses of radiation to the prostate gland while reducing the radiation exposure to nearby healthy tissues.
Three-dimensional conformal radiation therapy (3D-CRT)
3D-CRT uses special computers to precisely map the location of your prostate. Radiation beams are then shaped and aimed at the prostate from several directions, which makes it less likely to damage normal tissues. You will most likely be fitted with a plastic mold resembling a body cast to keep you in the same position each day so that the radiation can be aimed more accurately. This method seems to be at least as effective as standard radiation therapy with lower side effects.
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 lets doctors deliver an even higher dose to the cancer areas. Many major hospitals and cancer centers now routinely use IMRT.
Some newer radiation machines have imaging scanners built into them. This advance, known as image guided radiation therapy (IGRT), lets the doctor take pictures of the prostate and make minor adjustments in aiming just before giving the radiation. This may help deliver the radiation even more precisely, which may result in fewer side effects, although more research is needed to prove this.
A variation of IMRT is called volumetric modulated arc therapy. It uses a machine that delivers the radiation quickly as it rotates once around the body. This allows each treatment to be given over just a few minutes. Although this can be more convenient for the patient, it hasn’t yet been shown to be more effective than regular IMRT.
Another approach is to place tiny implants into the prostate that send out radio waves to tell the radiation therapy machines where to aim. This lets the machine compensate for movement (like during breathing) and may allow less radiation to go to normal tissues. In theory, this could lower side effects. So far, though, no study has shown side effects to be lower with this approach than with other forms of IMRT.
Proton beam radiation therapy
Proton beam therapy focuses beams of protons instead of x-rays 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 release their energy only after traveling a certain distance. This means that proton beam radiation can, in theory, deliver more radiation to the prostate while doing less damage to nearby normal tissues. Proton beam radiation can be aimed with similar techniques to 3D-CRT and IMRT.
Although early results are promising, so far studies have not shown that 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 very expensive, and they aren’t available in many centers in the United States. Proton beam radiation might not be covered by all insurance companies at this time.
Possible side effects of EBRT
Any numbers below used to describe the possible side effects 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: Radiation can irritate the large intestine and rectum and lead to a condition called radiation proctitis. This can lead to diarrhea, sometimes with blood in the stool, and rectal leakage. 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 EBRT, but the newer conformal radiation techniques may be less likely to cause these problems.
Bladder problems: Radiation can irritate the bladder and lead to a condition called radiation cystitis. You might need to urinate more often, have a burning sensation while you urinate, and/or find blood in your urine. Bladder problems usually improve over time, but in some men they never go away. About 1 man out of 3 continues to need to urinate more often.
Urinary incontinence: Overall, this side effect is less common than after surgery. The risk is low at first, but it goes up each year for several years after treatment.
Erection problems, including impotence: After a few years, the impotence rate after radiation is about the same as that after 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 EBRT, but some of these men had erection problems before treatment. About half of men who had normal erections before treatment 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 have problems with erections. Impotence may be helped by treatments such as those listed in the surgery section, including erectile dysfunction medicines.
For more about coping with erection problems and other sexuality issues, see our document Sexuality for the Man With Cancer.
Feeling tired: Radiation therapy may cause fatigue that may not go away until a few months after treatment stops.
Lymphedema: Fluid buildup in the legs or genitals (described in the surgery section) is possible if the lymph nodes receive radiation.
Urethral stricture: The tube that carries urine from the bladder out of the body may, rarely, be scarred and narrowed by radiation. This can cause problems with urination, and may require further treatment 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 be higher. Brachytherapy may not be as effective in men with large prostate glands because it might 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 are used to 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 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 lowers 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, the seeds cause 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 an overnight stay 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 higher Gleason score).
Temporary (high dose rate, or HDR) brachytherapy
This is a newer technique. Hollow needles are placed through the skin between the scrotum and anus and 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 after treatment, 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 bowel problems, urinary problems, and problems with erections.
Bowel problems: Significant long-term bowel problems (including rectal pain, burning, 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 men who have brachytherapy. This may be 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.
Erection problems: Some studies have found rates of erection problems to be lower after brachytherapy, but other studies have found that the 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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