If you have been following me on Facebook at Dr. Sue Cancer Vet, you know that last week I was lecturing with what I call “ASC Team CyberKnife.” This team includes radiation oncologist Dr. Sarah Charney, neurologists Drs. Rick Joseph and Jason Berg, and me, the medical oncologist. We manage all the CyberKnife patients that come to the Animal Specialty Center (ASC) in Yonkers NY.
So after work on two nights, we all traveled to Red Bank, NJ and then to Norwalk, CT to talk to veterinarians about CyberKnife RadioSurgery, what tumors it’s good for, and our experience over the last 4 years.
There is a lot of great information on radiation therapy in the Dog Cancer Survival Guide, but in case you haven’t read it yet, you should know that typically, radiation therapy is used for local disease control — to damage and ultimately kill the primary cancer, usually as a follow up treatment to surgery. For example, if a dog has an incomplete resection — which means that there are cancer cells detected in their surgical scar on the biopsy report (dirty margins) — we would follow the surgery with radiation treatments to “clean up” those microscopic cancer cells. This is pretty common when it comes to a mast cell tumor or a soft tissue sarcoma. These conventional radiation therapy treatments usually require fifteen to twenty treatments, which are also called fractions (see below). Each session requires a short anesthesia, and pets are usually treated daily Monday to Friday with the weekends off. That’s a lot of anesthesia.
Why SO many treatments? It’s all about the normal tissue in the radiation field. To minimize damage to the normal cells, the dose is divided up into many small treatments. These “fractions” are helpful because normal cells can repair themselves more efficiently after smaller, multiple doses. For example, if your dog has a tumor in the nose, conventional radiation therapy will probably expose other nearby body parts to the harmful radiation: the mouth, eyes, and brain may get radiation because it is in the treatment field.
It’s this damage to otherwise healthy tissue that has motivated oncologists to look for a way to deliver radiation with more precision, fewer side effects, and fewer treatment sessions. The new technique called radiosurgery aims at getting the radiation energy directly to the tumor – even inoperable tumors – while avoiding healthy body parts that might be damaged by the beam or by its scatter.
By the way, I personally think the radiosurgery name is silly because there is no surgery in radiosurgery. There is no actual cutting – the name is meant to imply that radiation is accomplishing what surgery would do if it could actually get to the tumor.
Radiosurgery is not good for every type of tumor (for example, mast cell tumors and soft tissue sarcomas are not good candidates). But it does offer hope to some patients whose tumors were once considered inoperable. Here’s why:
The new, modified linear accelerators (radiation therapy machines) can generate very controlled, narrow beams that deliver radiation very precisely. The machine has five “arms” and rotates around several axes. It can approach a tumor from almost any angle the radiation oncologist wants it to, and while a traditional linear accelerator has two to four ports (holes where the radiation exits), the CyberKnife has hundreds.
Planning the radiation is critical when you’re dealing with radiosurgery. First, a CT (computed tomography) scan is done to get a very detailed three-dimensional image of the tumor. (For brain tumors we need both a CT and MRI for planning.) Then, Dr. Charney, our radiation oncologist, uses a complex computer program to plan precise coordinates for the radiation beam.
The precision involved in radiosurgery is amazing, and it also makes radiation therapy more appealing to dog lovers. For example, a nasal tumor that requires fifteen to twenty conventional sessions and exposes the mouth, eyes, and brain to radiation can be treated in only three consecutive CyberKnife sessions. That’s five times less anesthesia, five times fewer trips to the hospital, and fewer side effects. And the results are comparable to traditional radiation therapy. Some brain tumors are treated in just one treatment. It is pretty amazing!
My practice was the first to offer CyberKnife Radiosurgery to animals, and we have been treating dogs and cats since March 2008. Currently, radiosurgery is only practiced at the University of Florida, Colorado State University, southern California, and my practice the Animal Specialty Center in New York.
In my next blog I will tell you what tumors we treat and our experience so far. Stay tuned – this is pretty exciting stuff!