External Beam Radiation Therapy

About Radiation Therapy
Radiation therapy is one of several methods used to treat cancer. The radiation comes from beams of high-energy waves or from streams of radioactive particles. Using specialized equipment and materials, radiation from these beams and particles targets cancer cells in order to kill them or stop their growth and spread. Normal cells are also affected by radiation so to protect them the amount of radiation that is given is limited over time. Normal tissue cells are shielded as much as possible during the treatment.  The rectum, which is just behind the prostate, is the structure that limits the total dose of local prostate radiation that can be delivered over one's lifetime.

Radiation therapy is most often used to treat localized cancer, that is, cancer that is still limited to the prostate gland, as well cancer that has spread to nearby tissue. The cancer may be in its early stage or advanced. However, patients in the early stage of the disease usually have a choice between surgery and radiation. Both therapies provide similar cure rates. Depending on how advanced the cancer is radiation can be used in concert with other therapies, such as chemotherapy or hormones.

Two main types of radiation therapy are available to treat prostate cancer: external beam radiation and brachytherapy (internal radiation). Both are affective in treating prostate cancer, although more long-term information is available concerning external beam radiation than brachytherapy. Depending on your medical history and what types of other therapy you may be receiving, your doctor will decide how much radiation you will receive and the number of treatments you will need.

External Beam Radiation Therapy
External beam radiation therapy involves a radiation source located outside the body. It is the type of radiation therapy used most often to treat prostate cancer. During the therapy, the patient lies immobile on a special bed while a linear accelerator delivers beams of radiation to precise areas of the prostate or if needed, to the surrounding area.

External beam radiation therapy is an outpatient treatment. It is given five days a week for roughly seven to nine weeks. Each session takes only a few minutes. Patients cannot feel, see, or smell the radiation; the therapy itself is painless. These short sessions allow the delivery of many small of doses of radiation as opposed to only a few large doses. It has been found that many small doses of radiation can help protect normal cells from damage.

The current standard of external beam radiation, known as intensity modulated radiation therapy (IMRT), may offer even better success rates with fewer side effects than traditional external beam radiation. Intensity modulated radiation therapy precisely maps the location of the prostate, so the prostate can receive more radiation and the surrounding tissue less, thus diminishing damage to normal tissue. Likewise, IMRT uses a linear accelerator that moves around the patient and uses several beams to deliver the radiation. The strength of each beam is set to minimize the amount radiation that reaches normal tissues while maximizing the radiation delivered to the cancerous tissue.

Image-guided Radiation Therapy
The newest versions of external beam radiation uses implanted markers to further precisely target the prostate, and its movement (up to 2 cm), during treatment.  Non-radioactive gold seed markers are used to check to location of the prostate before each daily treatment   Another method, the Calypso, uses tiny GPS beacons as implants, which signal back many times a second to the main aiming beam, giving even more accurate targeting during daily treatment. Emory is one of  only a handful of sites in the US performing this, starting in 2007. Both of these types of implants are placed by the urologist under local anesthesia with ultrasound guidance, similar to the prostate biopsy procedure.

A Radiation Oncologist can review these various treatments with you, and help in selecting the most appropriate option for your particular prostate cancer situation and overall health.

Possible side effects of external beam radiation therapy
Patients may experience some side effects, which include the following:

• Mild fatigue
• Urgency, frequent urination, burning sensation while urinating, blood in the urine, and irritation of the urethra
• More frequent bowel movements, diarrhea, blood in the stool, rectal leakage, and rectum soreness and irritation
• Impotence, which may develop over a few years, especially in older patients
  

Advantages of external beam radiation

• Survival rates are comparable to surgery at 5 to 10 years
• Outpatient treatment is convenient, with no hospital stay
• Image guided technology may improve results without more side effects 

Disadvantages of external beam radiation

• Erectile dysfunction occurs in up to 70 percent of patients
• May make urinary symptoms worse for several months until the prostate starts to shrink
• Incontinence, mainly urgency related, occurs in 1 to 2 percent of patients
• Chronic injury to the bladder or rectum occurs in 1 to 2 percent of patients
• Increased risk of bladder and rectal cancers about 10 years later
• Future treatments are limited by radiation therapy
  • Salvage surgery has high risk of incontinence and disease at the surgical margins
  • Salvage cryotherapy has low risk of incontinence and rectal injury