External Beam Radiation

Radiation therapy, like surgery, is a local treatment in that it directs radioactive beams to a particular area to kill cancer cells directly or indirectly, by cutting off their blood supply. External beam radiation has been used in the treatment of prostate cancer for over sixty years, so many medical professionals are skilled in its use.

External beam radiation uses a machine to produce and deliver high-energy radiation to the prostate and perhaps to the pelvic lymph nodes. Radiation therapy can be used alone to treat prostate cancer, or it can be combined with other treatments such as chemotherapy, hormonal therapy, or surgery. Sometimes, radiation therapy is performed after surgery.



Radiation works by interfering with the ability of cells to divide, and normal cells are affected as well as cancerous cells. Consequently, external beam radiation is given in small doses over about 7 to 8 weeks. Usually, men are treated each weekday (Monday through Friday), and no treatment is given on the weekends to allow healthy cells some time to recover. (Healthy cells can repair themselves faster than cancer cells.)

The aim of external beam radiation is to give as even and as high a dose of radiation as possible to the cancerous cells, while giving the lowest possible dose to surrounding, healthy cells. Unfortunately, the prostate is hard to target, and parts of the rectum, the bladder, and the urethra are inside the field of radiation (the area that receives the radioactive beams). Various techniques have been developed to enable the more accurate targeting of the prostate cancer and the protection of healthy tissue during external beam radiation. Some of these techniques are grouped under the name of conformal radiation therapy because they shape or conform the radioactive beams to the dimensions of the target area.

CONFORMAL RADIATION THERAPY
Two main techniques are used to enable precision in external beam radiation therapy: 3-Dimensional Conformal Radiation (3D-CRT) and Intensity Modulated Radiation Therapy (IMRT).

3-Dimensional Conformal Radiation
In this form of external beam radiation, a computer program, using a CT Scan or MRI, measures the prostate in three dimensions and calculates how the radiation should be delivered. Then, using the computer data, the radioactive beams are shaped so they conform to the area targeted to receive radiation. The accuracy of these measurements reduces the risk of damage to surrounding healthy cells and often enables higher doses of radiation to be delivered to the cancerous areas.



Intensity Modulated Radiation Therapy
This form of external beam radiation also uses a CT Scan or an MRI to create a three-dimensional picture of the prostate, and it uses computers to calculate how to irradiate particular areas while sparing others. IMRT differs from 3D-CRT, however, in that this process can deliver radiation at varying intensities or doses throughout the targeted field of radiation. In other words, the radiation’s intensity can be modulated, which enables the delivery of high intensity radiation to problem areas while reducing damage to other areas.


A Computerized IMRT Treatment Plan from the Buffalo Niagara Prostate Cancer Consortium

WHAT TO EXPECT
Before treatment, you will be asked to attend one or more radiotherapy planning sessions. Various tests and devices will help the radiation therapists determine the exact area to be treated. You will probably have a CT Scan, and you may be fitted with a cast or cradle that will be used to help you keep still and in position during radiotherapy. You may also have a urography, which uses a liquid injected into the urethra to give the medical team a better view of this duct. Because the prostate moves within the pelvis in relation to the fullness of the bladder and rectum, your radiation team may ask you to follow a routine to keep the prostate position fairly stable. You may have a second planning appointment at which the radiation team checks its work by performing a simulation. Often, marks are placed on your skin at this stage to enable radiation therapists to align the beams precisely each time.

During treatment sessions, you will lie flat and still on a treatment table. Your therapists will check the machine’s settings and adjust your position. They may use a cast or cradle to help you keep still and in an exact spot. When everything is ready, the therapist will leave the room and turn on the machine, which will send the high-energy beams into your body. These are painless. One session takes between 10 and 30 minutes, approximately, although the exposure to radiation itself lasts one a few minutes. Most of a man’s time is spent taking off and putting on outer clothes and getting into the proper position.

During the weeks of your treatment, you will have regular meetings with your radiation oncologist to monitor any side effects and review your progress.

After treatment sessions are complete, you will have follow-up appointments and tests (digital rectal exams and PSA tests) to check on the treatment’s efficacy.

POTENTIAL BENEFITS, DISADVANTAGES, AND SIDE EFFECTS

Benefits

  • External beam radiation therapy can offer an effective alternative to men whose age or poor general health make surgery or other treatments risky.
  • The treatment has a long history of use, so many professionals and medical centres are expert in its delivery and results and side effects have been documented and can be estimated with reasonable accuracy.
  • No hospitalization is necessary, and the daily treatments are fast, causing minimal disruption in a man's day if the radiation facility is nearby.
Disadvantages
  • The main disadvantage is that this procedure does not remove the prostate, so there is a risk that some prostate cancer will remain or will recur after radiation therapy.
  • A man may have to travel long distances to reach a radiation therapy facility, and, as the treatment program lasts for between 7 and 8 weeks, he may have to make arrangements to stay away from home during the weekdays for an extended period.
    • (Most Canadian radiation facilities have associated lodges where patients are accommodated during treatments, and various support groups and national organizations offer daily transportation services to and from treatment facilities.)


Side Effects
Side effects can be divided into two categories: those experienced during the course of radiation (immediate effects) and those experienced a while after treatment has ended (long-term effects). In both cases, not all men experience these side effects, and, the intensity and duration of any side effect experienced is variable, changing from man to man.

Immediate
As the effects of radiation are cumulative, these immediate side effects usually appear after a few weeks of radiation treatment and disappear some weeks after treatment has ended.

  • Some men experience fatigue, decreased energy, weight loss, or changes in appetite during radiation therapy.
  • A few experience gastrointestinal or rectal problems. The radiation of the rectum can cause rectal bleeding, cramps in the anus, pain during defecation, and the urge to defecate with no stool in the rectum.
  • Urinary problems are also possible because the radiation can inflame or irritate the prostate and the area surrounding it. Estimates are that men have about a 10 to 15 percent chance of developing either rectal difficulties or urinary problems, such as a burning sensation while urinating, an increase in urinary frequency (having to go more often), or an increase in urinary urgency (feeling as if you have to go more often).
Long-Term
When side effects occur during radiation, they commonly disappear once the radiation sessions are stopped and the body has time to recover. However, long-term side effects, which occur about 6 months after radiation or later, are permanent unless treated because they are caused by cellular changes or the build-up of scar tissue rather than by irritation.
  • Radiation can cause permanent infertility. Your chance of becoming infertile depends upon the dose of radiation administered. Sometimes, even if infertility is not permanent, it takes as many as five years for a man to reach normal fertility after external beam radiation
  • Erectile dysfunction is another possible side effect. Estimates are that a man has between a 25 and 50 percent chance of experiencing erectile dysfunction after radiation. ED usually occurs about 1 to 2 years after treatment.
  • Urinary frequency and urgency may increase because scarring has made the bladder less elastic.
  • Rectal problems are another possibility. The rectal lining may become fragile and bleed during defecation. Also, scar tissue in the rectum may increase the frequency of defecation.

Related information:

"Prostate Nomogram," Memorial Sloan-Kettering Cancer Center.

"High precision radiation therapy and a prostatectomy using laproscopy," CPCN

Dr. Victory Mak, "Notes on speech about coping with complications following radiation or a radical prostatectomy," CPCN (Newmarket Group)

Dr. Milosevic, "Notes on talk by this radiation oncologist regarding treatment options," CPCN (Newmarket Group)

Andrei Damyanovich, "Summary of investigation to improve intensity modulated radiation therapy," CPCN (CPCRI Grant Summaries-May 2004)

"PMH Pioneers Cone Beam CT," Forefront: Prostate Centre at Princess Margaret Hospital Update, Summer 2004, 2-3, CPCN

Dr. Patrick Cheung, "Summary of investigation on intensity modulated radiotherapy," CPCN (CPCRI Grant Summaries-Summer 2003)

Dr. Carole Lambert and Dr. Jean-Paul Bahary "Radioactive Cure: Radiotherapy is the treatment of choice in a variety of prostate cancer situations," Our Voice, Special Issue, 10-12

Different expertise, Different treatment: Do urologists and radiation oncologists tend to recommend the treatment that they themselves deliver? CPCN, July 2008.