This new method of radiation therapy has the potential to extend the survival time of dogs and eventually people.
Dr. Monique Mayer, a veterinary radiation oncologist at the Western College of Veterinary Medicine's Veterinary Medical Centre, is working with veterinarians across Western Canada to find canine patients that have been diagnosed with a malignant brain tumour.
If their owners are willing, the dogs may eventually receive MBRT through the research project.
"Dogs are ideal for this study," explains the project's principal investigator, Dr. Vijayananda Kundapur of the University of Saskatchewan's College of Medicine. "They actually have a fairly high incidence of brain tumour development, and one of the common types of brain tumour that happens in dogs is similar in histology to those found in human beings."
While brain tumours in dogs are treated almost exclusively with radiation therapy, the current treatment regimen for humans involves a combination of surgery, chemotherapy and radiation treatments.
Although higher doses of radiation achieve better results in terms of destroying or stopping cancer cells from multiplying, they can also damage the brain's normal structures and cause devastating short-term and long-term side effects.
The concept of creating tiny mini beams using synchrotron-generated X-rays is relatively new. An earlier study indicated that normal brain cells were unaffected when these mini beams delivered huge doses of radiation that damaged the blood vessels of the tumour cells and led to their eventual death.
"It took many years to understand the real effect of radiation treatment on the brain," Kundapur explains. "Over the years there can be continuous changes taking place that can directly or indirectly affect function, and we need to follow up so we can learn more about the long-term effects."
In a 2008 study involving mice, Kundapur used MBRT to deliver large doses of radiation that stopped the growth of brain tumours without causing damage to the brain. However, the mouse's relatively small brain size and short life span left many questions unanswered.
"It was a natural progression into a study involving the dog, a larger animal with a brain that nearly matches the human," says Kundapur. "I approached Dr. Mayer, and she was very positive about working on it with me."
With funding from the Saskatchewan Cancer Agency, Kundapur and Mayer began working with Drs. Gavin Cranmer-Sargison and Narinder Sidhu, medical physicists from the Saskatchewan Cancer Agency and the British Columbia Cancer Agency. Their research team also includes Dr. Susan Kraft, a veterinary radiologist at Colorado University who specializes in magnetic resonance imaging (MRI) of the brain.
The researchers' first step was building a collimator, a device that shapes the beams of a linear accelerator into the mini beams used for MBRT.
"The radiation is delivered in parallel slices," explains Mayer. "Instead of being a solid open field, it's split into tiny parallel beams."
Now that the collimator is working, the team is ready to begin the trial of this promising new radiation therapy. Clients who choose to include their dogs in the study will pay only a fraction of the regular treatment cost and will have their animals randomly selected to receive stereotactic radiation therapy or the mini beam radiation treatments.
Using CT and MRI images, Mayer and Kundapur will create a treatment plan that's tailored to each patient.
"Our patients include everything from little flat-nosed breeds to dogs with big heads, and that variation affects how the dose is computed," Mayer explains. "So once we create a plan that involves the best beam arrangement for each patient, that information is sent over to our linear accelerator and the patient undergoes treatment."
Each dog will receive an MRI before the course of three treatments, and the VMC pet radiation therapy team will encourage the owners to bring their dogs back for follow-up MRIs every six months. Researchers will also ask owners for permission to examine their dogs' brains once the animals have died.
Kundapur is enthusiastic about being involved in a collaboration that promises to benefit both animals and humans.
"If these animals live for years, then we know the tumour and the damage to normal cells was well controlled. Then by using MRI imaging and asking about behaviour changes, we can see if there's any later damage to their brain function," explains Kundapur.
"Finally the pathology will indicate other changes. We'll get the answers we need to take it to the next level – a human study."
Mayer is hopeful that the study will result in a treatment option that improves tumour control and ensures longer, healthy lives for dogs diagnosed with malignant brain tumours.
"We already have a good survival rate for dogs that have undergone radiation therapy for many types of brain tumours, but we're hoping we can increase that rate without an increased risk of long-term side effects."
To learn more about this canine research study, please contact Dr. Monique Mayer (email@example.com).