Darlene Cook wasn’t expecting a cancer diagnosis when her 10-year-old Golden Retriever Liberty (Libby) began limping. But MRIs of Libby’s chest, abdomen and bones revealed a localized bone cancer called an osseous plasmacytoma, and surgery was not an option.

“Because it is such a rare cancer, we didn’t have a lot to go on,” recalls Cook, “but the recommended treatment was radiation therapy. The original plan required 22 treatments, Mondays through Fridays, at the [nearby] University of Minnesota.”

One of the risks of radiation is the anesthesia and intubation necessary to administer the treatment. Some animals develop a cough after intubation that can turn into pneumonia. Libby started coughing on the third day.

Her luck changed when Cook heard of a cutting-edge treatment called CyberKnife® radiation therapy, which can deliver an entire dose of radiation in one to three treatments (versus 20 or more with traditional radiation). She packed up and drove 17 hours from Minnesota to the Veterinary CyberKnife Cancer Center near Philadelphia, PA, to pursue it.

Cyberknife radiation vs. conventional radiation

Libby’s inoperable bone tumor made her a perfect candidate for CyberKnife radiation, according to Dr. Siobhan Haney, VMD, MS, DACVR (RO) at the Veterinary CyberKnife Cancer Center. “If there are any areas of uncertainty — like when 99% of a tumor is removed by a surgeon but some cancerous cells remain — a much larger field of radiation is needed to blanket the area, and that’s when conventional radiation is ideal,” says Dr. Haney. “But when there’s a physical tumor visible to the naked eye or via MRI, we can target that tumor exactly with a large dose of CyberKnife radiation.”

Why the difference? CyberKnife radiation is delivered via an “intelligent” arm so accurate it can target the cancer within a 1-5 millimeter tissue margin. Conventional radiation delivers the treatment over a much broader field of 20-30 millimeters.

This accuracy is significant because CyberKnife targets only the cancerous cells, and spares the healthy organs and tissue surrounding a tumor from damage. Because the risk of harming healthy cells is virtually nonexistent, CyberKnife can administer a much stronger dose of radiation, which means the entire course can be delivered in fewer treatments.

“Bone tumors are tough to treat and there’s generally a poor prognosis associated with them,” says Dr. Haney. “Traditional radiation gives pets an average of maybe two to four months of survival time. With CyberKnife, we’ve seen pets survive six to 12 months. Not only can this make a huge difference to the pet owner, but the dogs are more comfortable because the side effects are so minimal.”

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Is CyberKnife safer for pets?

Typical side effects of conventional radiation therapy for pets include burns to the skin, swelling, ulcers, nosebleeds, and lethargy, among others; CyberKnife virtually eliminates these.

“I think CyberKnife is going to dramatically improve the quality of life for sick pets because it spares critical structures like the eyes, ears, mouth, and back of the throat from damage,” says Dr. Pam Lucas, DVM DACVIM (Oncology) at South Carolina Veterinary Specialists & Emergency Care. “For senior and geriatric pets, you worry about long courses of radiation because of the amount of anesthesia required, but with CyberKnife, you get the same benefit without as much strain on other vital organs like the heart and kidneys.”

Dr. Haney says patients often show signs of improvement after the first or second treatment. For Libby, the CyberKnife radiation improved her symptoms almost immediately.

The rewards of CyberKnife radiation can be great, especially in treating one of the most frightening cancers: brain tumors. “You can have a dog or cat who presents with severe clinical signs like circling, compulsive behaviors or aggression,” says Dr. Lucas, “but with appropriate therapy, the prognosis can be bright. Clients sometimes come in with a debilitated pet but after radiation, it’s like a light switch goes off and suddenly they have their old pet back again.”

If there is one drawback to CyberKnife, it’s that the technology is so new to veterinary medicine that it isn’t yet widely available. The Veterinary CyberKnife Cancer Center is one of just two facilities in the U.S. offering the treatment, and for many pet parents the $5,000 to $9,000 price tag — plus the burden of travel — can be prohibitive.

“I promote pet insurance to my clients,” says Dr. Cook. “When the time comes and there’s a costly decision to be made, pet insurance takes money out of the equation.”

Future uses in veterinary medicine

While it’s still early to determine the full effect veterinary CyberKnife can have on treating cancer in pets, so far we know it’s at least equivalent to conventional radiation in terms of survival times. The reduced number of treatments and fewer doses of anesthesia could mean that in time veterinarians will be able to escalate the radiation dose for a potentially better outcome.

“Right now we are on the cusp of a really exciting time in veterinary oncology,” says Dr. Lucas. “In the next five to 10 years, I think we’ll see more treatments [like CyberKnife] become available.”

Looking at a dog like Libby, whose age and type of cancer could have made her treatment both rough on her physically and risky for her health, CyberKnife seems to hold a lot of promise.

Dec 1, 2016
Pet Health

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