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External Beam Radiation Therapy

External beam radiation therapy uses a linear accelerator, a high-energy x-ray machine, to direct radiation to the prostate tumor. The procedure lasts a few minutes at a time, usually for five days a week, over the course of six to eight weeks.

Methods of Treatment Delivery

With the significant advancements in computer hardware and software, radiation therapy treatment, planning, and delivery have changed dramatically and will continue to progress during the next decade. Recent advances in radiation therapy more accurately target the tumor with higher doses of radiation, while minimizing damage to healthy, adjacent tissues.

Three-dimensional conformal radiation therapy aims radiation to the tumor from multiple directions. Sophisticated computers are used to very precisely map the location of the prostate tumor. During treatment, the patient is immobilized in a StyrofoamTM mold to aim this increased dose of radiation more accurately to the tumor and not onto adjacent tissues. Short-term results look promising, although studies of the long-term effectiveness of this therapy are not yet available.

Proton beam radiation therapy is similar to 3D conformal radiation therapy. However, instead of x-rays, this technique uses protons, parts of atoms that can pass through healthy tissues with little damage, while destroying tumor cells at the end of their path. As a result, proton beam therapy may be able to deliver more radiation to the tumor while sparing adjacent tissues. As with 3D conformal radiation therapy, short-term results of proton beam therapy look promising, although studies of long-term effectiveness are not yet available.

Intensity-modulated radiation therapy (IMRT) is a sophisticated, new technology that can shape and deliver a lethal dose of radiation to a tumor while sparing surrounding healthy tissues. The fundamental difference between conventional radiation therapy and IMRT is beam intensity; in conventional radiation therapy, the beam intensity is uniform, but in IMRT, the beam intensity varies across the treatment field. During IMRT treatment, where the tumor is the thickest, the beam intensity is at its maximum, and where the tumor is the thinnest, the intensity is at its minimum. Instead of the patient being treated with a single, large uniform beam, the patient is treated with several small beams, each with different intensities.

Treatment Planning - Example, Prostate Cancer

Radiation works more effectively on small and moderately sized prostate glands. Men with very large prostate glands often undergo a 3- to 6-month course of hormone therapy to shrink the prostate gland prior to radiation therapy.

Before radiation treatment begins, a planning session or simulation is required to pinpoint the tumor and determine the treatment series. Simulation may take up to an hour. The following steps occur during simulation.

A radiation therapist creates a thermoplastic or Styrofoam mold that supports your back, pelvis, and thighs. This mold, sometimes called a cradle, ensures accurate positioning over the course of your radiation treatments.

The CT scan is used to create a computer-generated 3D image of your pelvic anatomy, including prostate gland, bladder, rectum, and pelvic bones.

Lying in your mold again, you are aligned and x-rayed by a machine called a simulator. The simulator’s x-rays provide a picture of the tumor site and help determine how radiation will be directed to it. The beams of the simulator are positioned to deliver the appropriate dose of radiation to the prostate while sparing surrounding healthy tissues and structures. Beam positioning is then verified with a procedure called fluoroscopy.

Using the x-rays as a guide, the radiation therapist marks the treatment area on your skin. These marks serve as a temporary map of the treatment area and are used as a guide during treatment. At home, scrubbing with soap or using lotion on the marks will remove them. You can rinse your skin with water and pat it dry without removing the marks. After a few treatments, the outline is replaced with tiny permanent dots, called tattoos, which will not be removed with soap or lotion.

Before Receiving Treatment

Do not use moisturizers or medicated powders within two hours before your radiation treatment. It is best to keep the skin clean and dry to limit the possibility of a skin reaction to the radiation.

The Radiation Therapy Session

A radiation therapy session typically takes about 15 minutes. The therapist sets up the treatment according to the map on your skin and the information obtained from the simulation. You lie in the mold on the x-ray table. The linear accelerator moves in a circular fashion around the tumor area. The actual treatment lasts only a few minutes.

External beam radiation therapy poses no risk of radioactivity to the patient or to those with whom he comes in contact. You can continue normal activities with family and friends.

Follow-up Testing
A digital rectal examination (DRE) and prostate-specific antigen (PSA) blood test will be given every three to six months during the two years after treatment. After radiation treatment ends, PSA levels take between 18 and 24 months to reach their lowest point. (In contrast, after a radical prostatectomy, PSA levels drop to their lowest point immediately after surgery.) In the 24-month period after radiation therapy, PSA levels may bounce up and down from reading to reading. This fluctuation is normal and not a cause for concern unless three consecutive readings indicate a consistently rising PSA.

Advantages of External Beam Radiation Therapy

Radiation is an outpatient procedure that does not carry the standard risks or complications that accompany major surgery, such as surgical bleeding, post-operative pain, or risk of stroke, heart attack or blood clot. The procedure itself causes no pain. The risk of incontinence is minimal with radiation therapy.

(Sources) Zinreich ES, Derogatis LR, Herpst J, Auvil G, Piantadosi S, Order DE. Pre and post treatment evaluation of sexual function in patients with adenocarcinoma of the prostate. Int J Radiat Oncol Biol Phys 1990;19(3):729-32.