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Linear accelerator and other therapeutic tools vital in cancer treatment of dogs, cats

By Keener A. Tippin II

 

Humans get it. Dogs and cats get it too.

"It" is cancer and this often life-threatening disease is not only common in animals but also similar to cancer in humans. In using radiation therapy to treat pets stricken with cancer, oncologists at Kansas State University's Veterinary Medical Teaching Hospital have one of two treatment methods to apply -- either with a curative intent, hoping to control the disease for months or years or actually cure it, or palliatively, making the patient feel comfortable for as long as possible with the radiation therapy generated by a linear accelerator.

Rather than being a diagnostic tool like the MRI or CT scanner, the linear accelerator serves as a therapeutic tool in oncology treatment, according to Dr. Ruthanne Chun, an assistant professor of clinical sciences. Once cancerous lesions have been pinpointed using either the CT scan or MRI units, oncologists at the Veterinary Medical Teaching Hospital work with a radiation therapist to develop a treatment plan that will allow doctors to accurately treat the tumor exactly where it is. They hope to spare as much normal tissue surrounding the tumor as possible. The linear accelerator is shown in the photo below.

photo of linear acceleratorChun said with humans, radiation protocols tend to be much longer and more expensive than with pets. Like humans, animals are susceptible to side effects, depending on what part of the body is being radiated.

"If we're treating a nasal tumor and the eyes are in the field, sometimes an eye will still absorb some of that radiation energy," Chun said. Most dogs have long, stretched-out noses, so the nasal cavity sometimes extends back behind the eyes which can be sensitive to the effects of radiation. Careful therapists work hard to spare the eyes by doing a very special three-dimensional treatment designed by a radiation therapist.

Chun said the doctors watch for either short term or acute side effects that may occur within two to three weeks of starting radiation. Concern also exists for chronic or delayed side effects that may not arise until six to nine months after the radiation treatment.

"Specific problems you might see with the eye might be a decreased tear production or cataract formation or what we call retinal degeneration where the retina or the back part of the eye stops working the way that it's supposed to," Chun said. "So they may lose vision in the eye that gets a lot of radiation."

If a tumor is located on the leg, or on the paw, Chun said neither the eyes nor any other highly sensitive tissue areas are in the radiation therapy field.

"We still worry about what we call acute side effects," Chun said, "but that's usually just to the skin where they may have some redness and irritation but that resolves within a few weeks and the animals are usually fine afterwards."

Brachytherapy

Although rarely used now, another form of radiation therapy sometimes employed by oncologists is brachytherapy. When surgery can't be performed or isn't enough to remove cancerous tumors, veterinarians at the teaching hospital may use this implantable radiation treatment option for dogs or cats that have certain tumors that aren't likely to spread to other parts of their body.

After as much of the tumor as possible is removed, a hollow, sterile plastic tube called an "after-loading tube" is sutured into the tumor bed. After the wound is closed, Chun said the radioactive beads are essentially strung together on a plastic wire and fed into the after-loading tubes. Once clamped in place, they begin to emit a set amount of radiation into the tumor bed.

Once K-State was among only two or three veterinary colleges able to offer this service. Chun said the procedure is not offered at the teaching hospital as much any more because of health concerns. Chun said although a great advantage to brachytherapy is that it can deliver a very high dose of radiation just to where the tumor is and spare normal tissues a little bit more, a big disadvantage to the treatment option is that health care providers are exposed to a high level of radiation.

"If you're pregnant or young and want to have children, you can't handle it; you shouldn't be around those patients at all," Chun said. "It's the health of our doctors and our students here in the teaching hospital we are concerned about."

Chun said another disadvantage to that treatment option is that there are only certain locations where you can do brachytherapy on the body. Certain locations are very, very dangerous to perform brachytherapy in an animal. For example, if an animal has a tumor in its mouth and the oncologist puts the beads in its mouth and by accident it somehow swallows one, now the radiation is sitting in the animal's intestines, which weren't supposed to be radiated. This can cause a lot of trouble.

Chun stressed that no matter what type a cancer an animal develops, the animal's well being always comes first.

"It is very important for owners to know that any time we treat an animal for cancer, quality of life is as important to us as curing the cancer," she said. "So, even though we may use radiation or chemotherapy, we design our treatments so our patients will have a normal, happy and comfortable quality of life while going through therapy."

Spring 2003