The Medical Radiation Engineering - Radiation therapy for prostate cancer
The Medical Radiation Engineering
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دوشنبه 8 تیر 1394 :: نویسنده : Amir

Radiation therapy for prostate cancer

Radiation therapy uses high-energy rays or particles to kill cancer cells. Radiation may be used:

  • As the first treatment for low-grade cancer that is still just in the prostate gland. Cure rates for men with these types of cancers are about the same as those for men getting radical prostatectomy.
  • As part of the first treatment (along with hormone therapy) for cancers that have grown outside of the prostate gland and into nearby tissues.
  • If the cancer is not removed completely or comes back (recurs) in the area of the prostate after surgery.
  • If the cancer is advanced, to reduce the size of the tumor and to provide relief from present and possible future symptoms.

The 2 main types of radiation therapy are 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 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.

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 about 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.

Newer EBRT techniques focus the radiation more precisely on the tumor. This let doctors give higher doses of radiation 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, an advanced form of 3D therapy, is the most common method of EBRT for prostate cancer. It uses a computer-driven machine that actually moves around the patient as it delivers radiation. Along with shaping the beams and aiming them at the prostate from several angles, the intensity (strength) of the beams can be adjusted to limit the dose reaching the most sensitive normal tissues. This lets doctors deliver an even higher dose to the cancer.

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 might result in fewer side effects, although more research is needed to prove this.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 adjust 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. The machines that use this are known as Calypso®.

A variation of IMRT is called volumetric modulated arc therapy. It uses a machine that delivers 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.

Stereotactic body radiation therapy (SBRT)

This technique uses advanced image guided techniques to deliver large doses of radiation to a certain precise area, such as the prostate. Because there are large doses of radiation in each dose, the entire course of treatment is given over just a few days.

SBRT is often known by the names of the machines that deliver the radiation, such as Gamma Knife®, X-Knife®, CyberKnife®, and Clinac®.

The main advantage of SBRT over IMRT is that the treatment takes less time (days instead of weeks). The side effects, though, are not better. In fact, some research has shown that some side effects might actually be worse with SBRT as compared with IMRT.

Proton beam radiation therapy

Proton beam therapy focuses beams of protons instead of x-rays on the cancer. 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 safer or more effective than other types of EBRT for treating prostate cancer. 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

Some of the side effects from EBRT are the same as those from surgery, while others are different. The numbers below used to describe the possible side effects relate to standard EBRT, 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 cause 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. In the past, about 10% to 20% of men reported bowel problems after EBRT, but newer 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 out of 3 men continues to need to urinate more often.

Urinary incontinence: Some men develop urinary incontinence after treatment, which means they can’t control their urine or have leakage or dribbling. As described in the surgery section, there are different levels and types of 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. Problems with erections usually do not occur right after radiation therapy but slowly develop 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 can often 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: The lymph nodes normally provide a way for fluid to return to the heart from all areas of the body. If the lymph nodes around the prostate are damaged by radiation, fluid may collect in the legs or genital region over time, causing swelling and pain. Lymphedema can usually be treated with physical therapy, although it may not go away completely. To learn more, see our document Understanding Lymphedema: For Cancers Other Than Breast Cancer.

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 might 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 is also 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 might not work as well 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.

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 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 get 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 technique uses higher doses of radiation that are left in place for a short time. 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 over 2 days in the hospital, and the radioactive substance is removed each time. 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 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 get 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 might 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 cause bowel problems, urinary problems, and problems with erections.

Bowel problems: Bowel problems such as rectal pain, burning, and/or diarrhea can occur, but serious long-term problems occur in less than 5% of patients.

Urinary problems: Severe urinary incontinence is not a common side effect. But about 1 out of 3 men may have long-term problems with frequent urination. 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 a 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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دوشنبه 16 بهمن 1396 17:32
قابل توجه! پاراگراف در واقع بسیار جذاب است، من خیلی زیاد
ایده روشن در مورد این پست.
دوشنبه 8 تیر 1394 19:40
دوستان کسب درامد واقعی برای شمامنم اول فکر میکردم سرکاریه ولی رفتم میدونید چیه این یک سایته که هر روز تبلیغات گوگل میگره و شما با کلیک بر روی تبلیغاتش پول میگرید خیلی ساده است امتحان کن ضرر نمیبینی روز در نیاری 2000 تا 3000 هزار تومان
لینک اموزش سایت درامد زا
دوشنبه 8 تیر 1394 16:48
من یه سیستم تبادل لینک راه اندازی کردم که دارای بازدید خیلی بالاییه و علاوه بر اون یه لیست مفصل از وبلاگ های به روز و جذاب داره.سر بزن و اگه دوست داشتی تبادل انجام بده:-)

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