Radiation Therapy

Radiation therapy is a type of cancer treatment that uses beams of intense energy to kill cancer cells. The Washington State University Veterinary Teaching Hospital uses a linear accelerator, or LINAC, to accurately and safely direct radiation at tumors while protecting and limiting damage to surrounding healthy tissue. The teaching hospital is just one of a handful of veterinary hospitals in the Northwest with the technology.

Radiation therapy is frequently used to treat:

  • Mast cell tumors
  • Soft tissue sarcomas
  • Oral tumors – acanthomaous epulis, squamous cell carcinoma, fibrosarcoma, melanoma
  • Nasal tumors
  • Brain tumors

Chemotherapy is a form of cancer treatment in which a patient is given drugs designed to kill cancer cells. It treats the entire body and is often used for tumors that metastasize or spread throughout the body. Radiation therapy, however, is target to a specific area of the body where the cancer exists.

Radiation therapy works by the deposition of energy on or near DNA. Because the radiation damages DNA, cells die when they try to divide. Normal and cancerous cells are killed in the process.

Most animals being treated with radiation will undergo multiple rounds of radiation therapy with the goal of killing the maximum number of tumor cells while allowing time for repair and repopulation to occur in the normal cells. Animals are anesthetized prior to treatments.

Cancer cells are not all that different from normal cells. Their cell cycle and means of growth and division are the same as normal cells, but they have just lost their controls. The more aggressive the cancer, the more “out of control” the cells behave.

When a tumor is very small and essentially undetectable, it is a very metabolically active population of cells. Once the tumor becomes visible, it is already starting to slow down in its growth, and once it becomes a very large mass, it is actually a very slow growing, metabolically inactive population. Radiation acts primarily on rapidly dividing cell populations, so tumors should be treated when they are as small as possible.

Despite the best attempts at sparing normal tissues, there are side effects to radiation therapy. These can generally be divided into early and late effects.

Early effects happen within 3 months post-therapy, are expected, and will get better. They include hair loss, irritation of the skin caused, mucositis, and conjunctivits. Symptomatic therapy (and patience) is generally the best treatment and care must be taken not to damage the tissues further (animal scratching or human scrubbing). Acute edema will occur on rare occasions after radiation of nervous tissue and must be treated with high doses of corticosteroids until the symptoms resolve.

Late effects occur months to years after radiation and will not get better. Acceptable side effects include alopecia (hair loss) and hyperpigmentation of the skin and cataracts. Less acceptable effects would be nervous tissue atrophy or necrosis, bone necrosis, and skin fibrosis. These are serious side effects that may mean the treatment itself was done improperly.

Cancer of any kind is a diagnosis no pet owner wants to hear, but our board-certified veterinary oncologists can help you get an accurate diagnosis and develop a treatment plan. Call 509-335-0711 to schedule an appointment or visit our oncology webpage for more information.

This information is not meant to be a substitute for veterinary care. Always follow the instructions provided by your veterinarian. Washington State University assumes no liability for injury to you or your pet incurred by following these descriptions or procedures.