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What are external-beam and conformal external-beam radiation therapies? What are the side effects of EBRT?

External-beam radiation therapy (EBRT) is the use of radiation therapy to kill or inactivate cancer cells. The total radiation dose is given in separate individual treatments, known as fractionation. Cancer cells are most sensitive to radiation at different phases in their growth.

By giving the radiation on a daily basis, the radiation oncologist hopes to catch the cancer cells in the sensitive phases of growth and also to prevent the cells from having time to recover from the radiation damage. Con-formal EBRT uses CT images to help better visualize the radiation targets and the normal tissues. With three dimensional images, the radiation oncologist can identify critical structures, such as the bladder, the rectum, and the hip bones. This allows the radiation oncologist to deliver more radiation (72-82 Gy as opposed to 66-72 Gy with standard EBRT) to the prostate tissue but decrease the amount of normal tissue that is irradiated. The advantage of conformal EBRT over EBRT is that conformal EBRT causes less rectal and urinary irritation. The construction of an immobilization device (cradle) and the placement of small, permanent tattoos ensure that you are properly positioned for the radiation treatment each day. Through the assistance of computers, the radiation oncologist can define an acceptable dose distribution to the prostate and surrounding tissues, and the computer determines the appropriate beam configuration to create this desired distribution.

By giving the radiation on a daily basis, the radiation oncologist hopes to catch the cancer cells in the sensitive phases of growth and also to prevent the cells from having time to recover from the radiation damage.

Who is a candidate for conformal EBRT?

Men who are candidates for conventional EBRT are also candidates for conformal EBRT. Similar to other curative treatments, the ideal patient has a life expectancy of 7 to 10 years. In higher-risk patients, the increased radiation dose used with conformal EBRT causes a significantly better decrease in PSA progression than the dose used in conventional EBRT. There does not appear to be a PSA progression-free survival benefit with con-formal EBRT when compared with conventional EBRT in patients who have low-risk prostate cancer. Men who have a PSA level > 10 ng/mL or with a tumor that is clinical stage T3 are the most likely to benefit from the higher radiation doses that can be achieved with conformal EBRT. They may benefit from combination therapy, such as hormone therapy for 6 months plus EBRT. For patients with locally advanced or high-grade disease (Gleason score > 7) studies have demonstrated that 2 to 3 years of postradiation adjuvant therapy helps improve survival. The amount of radiation and the field of radiation differ for each individual and depend on the clinical stage and the Gleason grade. Contraindications to EBRT include a history of inflammatory bowel disease, such as Crohn's disease and ulcerative colitis or a history of prior pelvic radiotherapy.

What are the side effects and risks of EBRT and conformal EBRT?

The side effects of EBRT or conformal EBRT can be either acute (occurring within 90 days after EBRT) or late (occurring > 90 days after EBRT). The severity of the side effects varies with the total and the daily radiation dose, the type of treatment, the site of treatment, and the individual's tolerance. The most commonly noted side effects include changes in bowel habits, bowel bleeding, skin irritation, edema, fatigue, and urinary symptoms, including dysuria, frequency, hesitancy, and nocturia. Less commonly, swelling of the legs, scrotum, or penis may occur. Late side effects include persistence of bowel dysfunction, persistence of urinary symptoms, urinary bleeding, urethral stricture, and erectile dysfunction.

Bowel Changes

A change in bowel habits is one of the more common side effects of EBRT. Patients may develop diarrhea, abdominal cramping, the feeling of needing to have a bowel movement, rectal pain, and bleeding. Usually, if these side effects are going to occur, they do so in the second or third week of treatment.

Rectal pain can be treated with warm sitz baths, hydro-cortisone-containing creams (ProctoFoam HC, Cortifoam), or anti-inflammatory suppositories (Anusol, Rowasa).

Late bowel effects include persistent changes in bowel function, rectal fistula[1], or perforation (a hole in the rectum), and bleeding. Rectal fistula and perforation are rare and often require surgical treatment.

Skin Irritation

How skin tolerates radiation depends on the dose of radiation used and the location of the skin affected. The perineum and the fold under the buttocks are very sensitive and may become red, flake, or drain fluid. To prevent further irritation, avoid applying soaps, deodorants, perfumes, powders, cosmetics, or lotions to the irritated skin. After you wash the area, gently blot it dry. Cotton underwear and loose fitting clothes can help prevent further irritation. If the irritated skin is dry, topical therapies, such as petroleum jelly (Vaseline), lanolin, zinc oxide, Desitin, Aquaphor, Procto-Foam, and corn starch, can be applied.

Edema

Edema of the legs, scrotum, and penis may rarely occur, but when it does, it is more common in those who have undergone prior pelvic lymph node dissection. Lower extremity edema can be treated with supportive stockings, TED hose, and elevation of feet when sitting and lying down. Penile and scrotal edema is often difficult to treat.

How skin tolerates radiation depends on the dose of radiation used and the location of the skin affected.

Urinary Symptoms

The genitourinary symptoms of dysuria, frequency, hesitancy, and nocturia are related to changes that occur in the bladder and urethra that result from radiation exposure. The bladder may not hold much urine because of the irritation and scarring, and irritation of the bladder lining may make it more prone to bleeding. Bladder inflammation usually occurs about 3 to 5 weeks into the radiation treatments and gradually subsides about 2 to 8 weeks after the completion of radiation treatments. Urinary anesthetics (phenazopyridine HCL [Pyridium]) and bladder relaxants (antimuscarinic agents) may be helpful in decreasing the urinary frequency.

What is the success rate with EBRT/conformal EBRT?

The success rate varies with the initial PSA level. In one study, 89 to 92% of men treated with conformal EBRT whose pretreatment PSA was < 10 ng/mL showed no increase in PSA level at 5 years. Those with a pretreatment PSA of 10 to 19.9 ng/mL had an 82 to 86% chance of no increase in PSA level at 5 years, compared with a 26 to 63% chance of no increase in PSA at 5 years in men with a pretreatment PSA of > 20 ng/mL.

Men with T1 and T2 tumors have survival rates that are comparable to that with radical prostatectomy. In such individuals, the clinical tumor-free survival is 96% at 5 years and 86% at 10 years.

  • [1] An abnormal passage or communication, usually between two internal organs, or leading from an internal organ to the surface of the body.
 
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