"I think the advances in the field are going to be limited, in that there are very few of us who can do radiation therapy
with linear accelerators," says Green. "If people wanted to, they could purposely build a radiation therapy vault in their
practices to accommodate horses. But radiation therapy is not going to be a lucrative venture, so unless someone wanted to
subsidize that, it probably wouldn't be the best idea to deliberately build a vault for horses, unless you could also use
it to treat small animals. Ninety-five percent of what I do is small animals. This is due simply to the fact that horses don't
get a lot of tumors."
However, there are advances in human radiotherapy, including intensity-modulated radiation therapy (IMRT), radiosurgery and
IMRT is a procedure that uses multiple radiation beams from multiple angles. The beam shape changes during treatment to allow
more precise delivery of radiation dose to the tumor with better avoidance of normal tissues. Like conventional radiation
protocols, it requires multiple anesthetized treatment sessions. IMRT can be done with a conventional linear accelerator equipped
with a multileaf collimator. It also requires cross-sectional imaging of the body part and a 3-D computerized treatment planning
system to determine radiation dose delivery.
IMRT is being investigated in small-animal patients, but it has not been reported in horses. Auburn University's College of
Veterinary Medicine has onsite computed tomography (CT), magnetic resonance imaging (MRI) and a linear accelerator with a
multileaf collimator accessible for horses and can accommodate IMRT for horses, but it has not yet used the procedure, according
to William Brawner, DVM, PhD, Dipl. ACVR (radiology and radiation oncology), a professor at Auburn's College of Veterinary
Medicine. The challenge of doing IMRT in horses is that their body sizes limit the precise and repeatable positioning required
and also make it difficult to allow the linear accelerator gantry to rotate around the patient to deliver the multiple beam
angles. Linear accelerators are designed for people; none are designed for animals, and especially not for large animals.
The tumor's location and size, the ability to obtain cross-sectional images and the ability to position the patient for gantry
rotation will be important considerations in case selection. It's likely that only tumors of the head and extremities of horses
will be accessible for IMRT.
A new equine radiation oncology unit is being built at Texas A&M College of Veterinary Medicine and Biomedical Sciences (TAMU
CVM). The Diagnostic Imaging and Cancer Treatment Center (DICTC) is a state-of-the-art research and clinical facility that
will contain about 9,000 square feet dedicated to advanced diagnostics, radiotherapeutics and translational research. The
DICTC includes a 40-slice configuration SOMATOM Sensation Open CT scanner (Siemens), a wide-bore MAGNETOM Verio 3T MRI scanner
(Siemens) and a TomoTherapy Hi·Art treatment system (TomoTherapy).
Michael Deveau, DVM, Dipl. ACVR (radiation oncology), a clinical assistant professor at TAMU CVM, says, "The facility signals
a major new material and intellectual commitment on the part of TAMU CVM toward advancing research and improving veterinary
patient health care."
TAMU CVM purchased a helical TomoTherapy system and has exclusively dedicated it for veterinary patient image-guided radiotherapy.
The ring-based TomoTherapy platform combines integrated CT imaging with conformal IMRT to deliver sophisticated and unmatched
radiation treatments with speed and precision while reducing radiation exposure to surrounding healthy tissue. "It's a flagship
product in veterinary radiation oncology," says Deveau. Access to a TomoTherapy system for veterinary patients is limited
to only two institutions worldwide: TAMU CVM and the University of Wisconsin-Madison Veterinary Medical Teaching Hospital.
Only Texas A&M intends to treat large animals, says Deveau.
"Ring-style gantry systems like the Hi·Art treatment system aren't specifically designed for large animal use," says Deveau.
"Of course, the same can be said for any of the linear accelerators. The systems are designed for attributes encompassing
the human silhouette. It's fortunate we're able to translate the use to such a wide range of species and clinical presentations
in veterinary medicine."
The DICTC is scheduled to start treating small-animal patients in September. Integration of large animals will be limited
initially to the weight limit of the system's couch (425 to 450 lbs.). Active research and development is under way to integrate
an independent couch system for large animals weighing more than 450 lb, but it's currently not ready for clinical implementation.
Ed Kane, PhD, is a researcher and consultant in animal nutrition. He is an author and editor on nutrition, physiology and
veterinary medicine with a background in horses, pets and livestock. Kane is based in Seattle.