Radiation for Equine Cancer Offered by Washington State

During the past few years, the oncology team at Washington State University (WSU) has successfully treated several horses with cancer using radiation therapy. Previously, this type of treatment was considered an unrealistic option for horses with cancer.

But WSU's advantage is its linear accelerator. One of the most advanced machines in the world dedicated to animal cancer treatment, the linear accelerator in WSU's Veterinary Teaching Hospital uses either electron beams or high-energy X ray radiation to treat tumors with minimal impact to the surrounding healthy tissue. This tool delivers focused radiation therapy exactly like that used with human cancer patients, while being large enough to accommodate a horse.

WSU oncologist Janean Fidel, DVM, MS, Dipl. ACVR, ACVIM, believes radiation therapy is a highly viable option for treating numerous equine tumors, including common skin tumors such as melanomas, sarcoids, and squamous cell carcinomas.

"Even though cancer is not as common in horses as dogs or cats, it does still occur and, just like in small animals, radiation therapy is a valuable tool in the treatment of our equine oncology patients," said Fidel, who works with WSU's equine team to treat horses that come to the Veterinary Teaching Hospital in Pullman.

Recently, Fidel presented her findings at the American College of Veterinary Internal Medicine (ACVIM) Forum, entitled, "Radiation Therapy in Horses: Something to Consider." (Read coverage of this presentation.)  


Ghostbuster undergoing radiation treatment for cancer

Ghostbuster receiving radiation treatment in WSU�s linear accelerator under the care of the WSU equine surgical team.

According to Fidel, tumors located on extremities or the head are easier to position, but any body part that fits under the beam can be treated. After reviewing the biology of radiation therapy in dogs and cats, Fidel said the goal remains the same: Deliver the highest possible dose of radiation to the tumor while sparing the normal surrounding tissue. Under this model, she believes that only tumors that have not or do not have a tendency to metastasize should be considered.

Treating horses presents several challenges because of their size and the number of treatments required. But the WSU equine team and Patrick Gavin, DVM, PhD, Dipl. ACVR, a WSU radiation oncologist, developed a method of anesthetizing horses, and moving them to and from the linear accelerator in a safe and rapid manner. Gavin has since retired and Fidel now develops the protocols to be used for individual horses.


In one sterling example, WSU veterinarians were successful in treating a Clydesdale/Thoroughbred cross named Ghostbuster in 2005. At 1,400 pounds, Ghostbuster was the largest animal to be treated in WSU's linear accelerator.

"We used a protocol where we anesthetized (and treated) Ghostbuster twice a day for five days," said Kelly Farnsworth,MS, DVM, Dipl. ACVS, a WSU a professor and equine surgeon at WSU who was involved in the case. "This protocol had not been used in horses before. Typically the procedure from the time he was anesthetized to the time he was back in the recovery stall was around 12 to 13 minutes. The treatment in the linear accelerator lasted only about 25 to 30 seconds, and the rest of the time was transporting him to and from the linear accelerator. He came through the treatments without any problems at all."

Better yet, Ghostbuster's tumor completely regressed. Years later, the horse remains free of cancer.

"The results of this therapy in other species and certainly in this horse have been very encouraging," Farnsworth said.--Darin Watkins and Emmy Widman


Reprinted from the WSU College of Veterinary Medicine Equine News Fall 2008 issue.

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