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Treatment for Prostate Cancer: External-Beam Radiation Therapy

If you have localized prostate cancer that needs curative treatment, you have two good options:  Radiation and surgery.  (You can read more about surgery here.)  More than 60,000 American men opt for radiation every year, and the cure rates are excellent.  It doesn’t require anesthesia, and this makes it an especially good option for older men, or for men with heart problems or other health issues that might rule out surgery.  Also, because it is done in an outpatient setting, most men are able to continue working right through the treatment.

Radiation doesn’t kill cancer cells immediately – but it causes their DNA to take a big hit, and sabotages their ability to reproduce. The damaged cancer cells die off, and the body gets rid of them.  Meanwhile, although normal cells are affected by the radiation therapy, too, they are able to repair themselves.  

“The goal,” says radiation oncologist Phuoc Tran, M.D., Ph.D., “is to deliver a powerful dose of radiation that will kill the cancer, but to do it as precisely as possible so that we cause minimal damage to the healthy tissue around it – the urethra, rectum, and bladder.”  

Although each actual treatment doesn’t take very long – most treatments take less than 20 minutes, tops, including the time to get you properly situated on the table – there’s a lot of work that happens before you ever get that first dose; measurements, calculations and imaging, with the help of sophisticated computer software, all to create a personalized treatment plan and detailed map of your particular pelvic terrain, so doctors know which areas to target, and which to avoid.  

External-beam therapy, as its name suggests, means high-energy beams of radiation delivered from the outside.  A different kind of radiation therapy, called brachytherapy (implantation of radiation seeds), is actually delivered from inside the body and is discussed here.

External-beam therapy is used as a curative treatment in men with localized prostate cancer (stages T1 or T2), or with locally advanced disease.  Sometimes it is given in conjunction with brachytherapy.  For men who have a high risk of prostate cancer recurrence, external-beam therapy is combined with two to three years of hormonal therapy, and has been shown to make a significant improvement in survival compared to radiation alone.  (Why two to three years of hormonal therapy?  That’s a good question; it may be that a shorter course of hormonal therapy will prove just as effective, but no one has definitely proven this just yet.  However, findings from one recent trial suggest that 18 months may be long enough to achieve the same results.)  

External-beam radiation therapy can also be very helpful to men with advanced prostate cancer.  It can ease pain in the bones and reduce the likelihood of having a fracture.

Who is the best candidate for radiation?  “Anyone with prostate cancer,” Tran states, “no matter what his diagnosis.  He should expect to live at least five more years, and be willing and able to come for treatment for six to nine weeks.  Most of the men we treat here at Johns Hopkins are in their 60s, although at other centers, radiation oncology patients tend to be in their 70s.”  

Traditionally, younger men with prostate-confined cancer who could benefit from definitive therapy and otherwise are in good health have been steered toward surgery, and older men have been steered toward radiation.  This is because, Tran explains, “there was a sense in the prostate world that if a man has many more years to live, there is an intrinsic value in removing a cancerous organ so it can never regenerate more cells.”  Also, it is easier from a medical standpoint for a man to have radiation after surgery, if cancer comes back, than to have surgery after radiation.  “However, more recent studies have shown that men younger than 60 with prostate cancer who are treated with radiation do equally well as men older than 60.”

There are health concerns that affect both forms of treatment; for men with heart problems or certain other conditions, radiation may be safer for their overall health.  Similarly, men with diabetes are at higher risk of developing side effects from radiation therapy.  “Since he already has disease in the small vessels, radiation will put him at a slightly elevated risk of rectal bleeding, and the diabetes can also affect his ability to heal after radiation treatment.”

It also depends on you.  Are you a surgery or a radiation guy?  “If you can’t bear the thought of having cancer in your body and you want it out, then you’re a surgery person,” says Tran.  “If you have a fear of radiation, then surgery may also be for you.  But if you don’t like the idea of general anesthesia and of being cut open, then maybe you are a radiation person.”

Another point to consider:  “Surgery has a clear end point.  When you take out the prostate and the cancer is gone, your PSA will become undetectable.”  With radiation, the PSA may never become undetectable – because the prostate is still there.  Instead, the PSA slowly sinks to reach a low point, called a PSA nadir.  “It can take one and a half years for the PSA to reach its lowest point, and even after that, you may experience minor fluctuations.”

Adam Dicker, M.D., Ph.D., Chairman of Radiation Oncology at the Sidney Kimmel Cancer Center at Thomas Jefferson University, says that “with radiation, because you’re not eliminating the gland, it takes a while for PSA to drop. Just as it takes a long time for prostate cancer to develop, it takes a long time to die off.  It can take six months to a year and a half for PSA to get to its lowest level.”  Sometimes men can experience a “bump” in their PSA, where it bounces up, then goes back down. Biochemical relapse – when cancer is thought to have come back – is defined as whatever that PSA nadir is, plus 2 ng/ml.  

The goal, Tran adds, is for the PSA to go under 0.1 ng/ml – the definition of undetectable – “and stay there forever.”  However, “PSA values under 1ng/ml are also completely acceptable.”  You will have PSA tests every three to six months for the first several years after treatment.  If the PSA reaches its low point and stays put for several consecutive measurements, then you can start to get PSA tests less frequently – every six months to a year.  And after that, if it remains stable, you may go to yearly PSA tests.

If you don’t want to live with the uncertainty of watching your PSA slowly drop, and if you might worry if it fluctuates, then radiation may not be for you.  

“If this uncertainty would bother you so much that it would affect your quality of life, surgery may be a better option for you.”  Phuoc Tran, M.D., Ph.D

However, if you’re okay with waiting for the PSA nadir, and if you don’t mind getting treatment over the course of a few weeks instead of in one operation, then “radiation may be ideal for you.”  

What are my options?

Conventional external-beam radiation therapy is given in little doses, a few minutes a day, five days a week, for seven or eight weeks.  These small doses minimize the injury risk for the healthy tissue near the tumor.  Scientists measure radiation in units called Gy (pronounced “gray,” after an English physicist named Louis Harold Gray).  Most men get a minimum total dose of 75.6  Gy, but could get as much as 81 Gy; this works out to 2 Gy or less per day.  

The treatment itself is painless – just like getting an x-ray at the dentist’s office.  But one big challenge with getting repeated treatments is making sure you’re always in the exact same position, so the radiation can hit the target the way it’s supposed to.  Thus, you will be custom-fitted with your own “pelvic immobilization device,” which will not only keep you from fidgeting, but will make sure you’re not slightly higher and to the right on the table one day, and slightly lower and to the left the next.  

When you get fitted for your device, you will have a CT scan, so doctors can get a 3D look at your prostate.  Then, when you get the radiation, you won’t just get it from one side, but from multiple directions, and each beam of radiation will be individually shaped to target the cancer and a 5- to 10-millimeter margin of healthy tissue around the prostate.

Here are some of the specific forms of external-beam therapy (note:  they all end with the letters, “RT,” for radiation therapy, so it can be a bit confusing at first trying to tell them apart)

3DCRT (Three-Dimensional Conformal Radiation Therapy):  3DCRT uses CT scanning to plot your exact anatomy (everybody’s different in size and exact shape of, and distance between, structures in the pelvis), and to come up with the optimal radiation dosages.  “3DCRT can accurately use a patient’s unique anatomy to deliver radiation exactly where he needs it, while avoiding the bladder and bowel,” says Tran.  This ultra-precision allows doctors to maximize the radiation dose to the tumor, but also conforms, or “sculpts” the dose, to you individually.

IMRT (Intensity-Modulated Radiation Therapy):  IMRT, like 3DCRT, uses high-tech computer software and relies on more than 100 digital CT scans to build a 3-dimensional picture of the prostate tumor, but it is “even more conformal than 3DCRT,” says Tran.  “What’s so innovative with IMRT is that we can modulate the intensity of each beam during treatment with a multileaf collimator.”  Think of shutters on a window; the leaves are like slats that allow the collimator to filter the radioactive rays.  “The longer a leaf stays open, the stronger the dose of radiation,” says Tran.  “This allows us to sculpt the dose even more precisely to treat specific parts of the prostate with higher or lower dosages, in an infinite number of patterns, to within a millimeter of a cancer site.  We can maximize the dose of radiation to the bulk of the tumor, and minimize the dose that affects the healthy tissue nearby.”  This means less “collateral damage” to noncancerous tissue that’s just minding its own business right next to the tumor in the bladder and rectum – and fewer side effects.

IGRT (Image-Guided Radiation Therapy):  This approach has a lot of flexibility, because the radiation oncologist uses CT scans images to pinpoint the exact location of the prostate each day.  Now, you may be thinking, “My prostate is right where it always was,” and this is true – however, it can move around in there by as much as a centimeter, depending on how full your bladder and rectum are.  “Another good thing about IGRT is that we can adapt the treatment if a man loses weight,” says Tran.  Using the daily CT scans, doctors compare today’s images with yesterday’s and fine-tune the treatment accordingly.

Side effects of radiation treatment:  The good news here is that with ever-more- precise treatment, side effects are lower than ever.  Caveat:  To make sure that you have the lowest risk of side effects and complications, it is extremely important that you do your homework up front and find the best radiation oncologist and treatment center. If you don’t, you may regret it forever.

Short-term complications:  You may experience some temporary urinary symptoms, such as waking up in the night and needing to urinate, needing to urinate more often during the day, or urgency – needing to urinate right now, and not being able to hold it in for a long time.  Tell your doctor; there are medications that can help reduce acute symptoms.  You may also experience some rectal problems, including the need to have a bowel movement more often than usual, or loose stools.  Diarrhea is rare, but if needed, there are medications that can help. Your doctor may also suggest that you try a low-fiber diet for a while.

Long-term complications:  The risk of long-term problems after radiation therapy is very low, less than 5 percent.  These may include proctitis (rectal inflammation), cystitis (bladder inflammation), urinary or rectal bleeding, narrowing of the rectum or urethra, chronic diarrhea or urinary frequency or urgency, or development of an ulcer in the rectum.  All of these can be treated.  

“Also, exposure to radiation itself is a known carcinogen,” Tran notes.  “However, the most balanced data suggest that the risk of a man developing a second cancer from radiation treatment for prostate cancer is similar to the risk of death from general anesthesia during surgery.”  (That risk is less than 1 percent, in case you wondered.)  “The risk of that second cancer causing your death is likely even less.”

Erectile Dysfunction:  If your doctor tells you that getting radiation will spare you from having problems with sexual function, you might want to look for another doctor.  That’s not true.  The difference is, it may take several years for ED to manifest itself.  “It could be the result of damage from radiation to the small blood vessels or nerves that control erection,” says Tran, “or it could be damage to the penile bulb, which sits just below the lower part of the prostate.”  The Prostate Cancer Outcomes study showed that 63 percent of men who underwent radiation therapy had ED five years after the procedure.  “Just as with surgery, younger men and men who did not have any problems with ED before the procedure are the most likely not to have problems with potency afterward.”  The good news is that at least half of men who have ED after radiation therapy can be helped by drugs like Viagra, Cialis, and Levitra.  ED treatment is discussed in greater depth here.


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Janet Worthington
Janet Farrar Worthington is an award-winning science writer and has written and edited numerous health publications and contributed to several other medical books. In addition to writing on medicine, Janet also writes about her family, her former life on a farm in Virginia, her desire to own more chickens, and whichever dog is eyeing the dinner dish.