Radiation Oncology
Introduction
Many dogs and cats have tumors that cannot be removed completely using surgery. Radiation therapy is a valuable tool to use to treat the tumor in such patients. Highly trained veterinarians, called radiation oncologists, and technologists administer radiation therapy.
Radiation therapy has been available at the College of Veterinary Medicine since 1984. Between 150 and 200 patients receive radiation annually. Our recent move into a new hospital allowed an upgrade in technology to a linear accelerator with a multi-leaf collimator and IMRT (Intensity Modulated Radiation Therapy) capabilities.
Our Linear Accelerator
A linear accelerator is a very sophisticated x-ray machine. The accelerator can rotate around the patient, allowing it to be positioned optimally to deliver the radiation to just the right location. Here you can see the new accelerator during installation and testing. Our new machine with a multi-leaf collimator allows very conformal radiation therapy (CRT) delivery for improved tumor control while sparring more surrounding normal tissue.
Irradiation with Photons
A photon is another name for an x-ray. The photons produced by a linear accelerator are very energetic, much more energetic than the photons used to make dental or chest radiographs (x-rays) for example.
Patients are under general anesthesia when they receive their radiation treatment. The treatment is not painful, but they must lie very still so that the photons can be directed onto the tumor in the most optimal fashion. The photo below shows an anesthetized cat receiving treatment with photons.
Radiation is planned using computed tomography (CT) to locate the tumor and to simulate the radiation dose in tissue. The following is an example of how radiation therapy is planned. This is a CT image of a cat with a tumor on the back (the bulge at the top). The green box represents the edge of the irradiated area and the colored lines represent various radiation doses. This planning technique optimizes the accuracy of treatment.
Irradiation with Electrons
One advantage of a linear accelerator is the option of using electrons for treatment rather than photons. Electrons are small particles that do not penetrate the body very far. Thus, superficial tumors, possibly located over sensitive organs like the kidney, can be more effectively treated.
For electron treatment, a cone must be used to confine the distribution of the electrons to the desired area. The photo shows a dog receiving radiation therapy using electrons. The treated area is over the abdomen. Photons could not be used for this type of treatment as they result in excessive dose to important organs.
Summary
Residents of North Carolina, and surrounding states, are fortunate to have access to such highly sophisticated treatment for their pets with cancer. Hundreds of pets are helped each year through administration of radiation therapy at our College of Veterinary Medicine.