Pet Columns, Office of Public Engagement, College of Veterinary Medicine at the University of Illinois at Urbana-Champaign

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Radiation Therapy Cures Some Pets and Comforts Others

Pet Column for the week of January 15, 2001

Office of Public Engagement
2001 S. Lincoln Ave.
Urbana, Illinois 61802
Phone: 217/333-2907
By Carrie Gustavson
Information Specialist

Most people are aware of the use of radiation therapy to treat cancer in people, but they don't realize that radiation therapy is also commonly used to treat certain cancers in animals. "Many tumors thought untreatable in the past are responsive to radiation therapy. With this approach, we can control and even cure more cancers in animals," says Dr. Joseph Impellizeri, resident in oncology at University of Illinois Veterinary Cancer Care Clinic.

Cancer occurs when a cell loses the ability to control its own growth. These abnormal cells quickly multiply, forming tumors. Radiation therapy is the use of high-energy radiation, similar to x-rays, but in doses many times higher than those delivered by x-rays. Radiation therapy works by damaging the cancer cell's DNA. The more cells multiply, the more sensitive they are to radiation, so cancer cells are affected by radiation more than normal cells are. Once the DNA is damaged, cancer cells are no longer able to divide and grow, so the tumor shrinks.

There are basically two approaches used with radiation therapy -- curative and palliative. If the desire is to cure the cancer, a much more intensive protocol, which usually requires outpatient visits for 16 to 20 days, is used. Palliative radiation therapy is a less intense protocol, and can be described as "comfort care." It is treatment intended to maintain a good quality of life for patients in which long-term cancer control is not possible. Palliative radiation therapy can be used to control pain, bleeding, and loss of function. The goal is to provide relief from the symptoms of cancer, not to cure the cancer or increase survival time.

Dr. Impellizeri takes into account the entire animal when making recommendations for radiation therapy. "Treatment is based on the responsiveness of a particular cancer to radiation, other underlying disease, and the economic concerns of the owner," he says. "Most animals do extremely well with radiation therapy if an appropriate workup is done beforehand to confirm that no other disease is present."

Radiation therapy is an effective treatment for many types of cancers in almost any part of the body and can be utilized alone or in combination with chemotherapy and surgery. "We commonly use radiation therapy as an adjunct to treating many types of inoperable cancers, such as lymphosarcoma, mast cell tumors, carcinomas (skin cancer), and sarcomas (cancer of bone, muscle, or connective tissue). Some of these cancers will respond to radiation therapy and provide the animal a good quality of life," says Dr. Impellizeri. Radiation therapy can also be used before surgery to shrink very large tumors or after surgery to kill cancer cells that may have been left behind.

Radiation therapy treatments are performed while the animal is under general anesthesia, using a machine that directs a beam of high-energy rays at the tumor. The treatments take only a few minutes and are normally done on an outpatient basis.

The side effects of radiation therapy are usually outweighed by the benefits of killing the cancer cells. Side effects depend on the area being irradiated but may include a sunburn-type skin reaction, hair loss, inflamed mucus membranes, and diarrhea. "Not all animals develop side effects, but if they do it is usually a self-limiting problem that goes away within three weeks after completing the radiation therapy protocol," says Dr. Impellizeri.

As with humans, early detection of cancer in animals increases the chance for a long, healthy life, so take advantage of the good care your local veterinarian can provide for your pet. He or she can provide you with a referral to the University of Illinois Veterinary Cancer Clinic if cancer is suspected or confirmed in your dog or cat.