Stereotactic radiation is an exciting, new type of radiation therapy that is changing how veterinary oncologists (cancer specialists) treat animal cancers.
“We’ve made a remarkable leap in treatment options,” said Dr. Rod Page, Director of the Flint Animal Cancer Center, Professor of Medical Oncology at Colorado State University’s College of Veterinary Medicine and Biomedical Sciences, and principal investigator of Morris Animal Foundation’s Golden Retriever Lifetime Study. “We are doing more stereotactic radiation therapy, and fewer surgeries, in our patients for a variety of cancers.”
Back to Basics – how radiation kills tumors
When applied to any cell, radiation disrupts the activity of key cell molecules – primarily DNA – crippling the cell and eventually leading to cell death.
Dividing cells are more sensitive to radiation therapy, but cells are not always actively multiplying. Cells cycle through a number of different stages as they grow and divide, including resting phases and growing phases. Early researchers recognized this phenomenon, and recommended that radiation treatments be divided into multiple small treatments called fractions. Dividing treatment over several days increases the likelihood of finding dividing cells and permanently damaging them.
Radiation exposure is a known risk factor for developing cancer, so how can it treat cancer, too? Radiation causes cancer by the same mechanism it kills tumor cells – through alteration of a cell’s genetic material. The differences between radiation therapy and cancer-causing radiation include the duration of exposure and the tissues exposed.
For example, lots of skin exposure to low-dose UV radiation over time (such as tanning) can lead to skin cancer. X-rays and gamma rays are other types of radiation that cause cancer, as seen in the use of atomic bombs in Japan and the Chernobyl nuclear accident. Many survivors of these incidents have been diagnosed with post-exposure cancers, with some cancers taking years to develop.
Because radiation can be friend or foe, oncologists have searched for better and safer ways to deliver radiation to cancer patients. Stereotactic radiation arose from this quest to harness the power of radiation to benefit cancer patients while decreasing collateral damage to other tissues.
Stereotactic radiation therapy uses high-dose, targeted radiation that is precisely focused on a tumor. The technique requires sophisticated imaging and newer radiation delivery vehicles, but the results are a significant improvement over standard radiation therapy, with very little damage to the surrounding normal tissues. Another benefit of stereotactic radiation is that because of its precision, higher doses can be delivered at one time, reducing the number of treatments. This in turn decreases damage to healthy tissue, and reduces the number of times a patient must be anesthetized.
More and more treatment centers are acquiring the ability to perform this type of therapy, but it still requires the expertise of oncology and radiation specialists for diagnosis, planning and administration.
Types of cancer treated with stereotactic radiation
Not all cancers respond to radiation therapy, or their location makes it impossible to safely deliver adequate therapy without damaging an unacceptable amount of normal tissue. The good news is that many types of tumors respond well to stereotactic radiation. These include some brain, nasal, bone, thyroid, lung, chest and pelvic tumors. Stereotactic radiation also can be used as a palliative therapy to shrink tumors and make patients more comfortable.
Risks of stereotactic radiation therapy
Stereotactic radiation requires general anesthesia for each treatment. Treatment time is often only 10 or 15 minutes, and major advances in anesthesia have made it much safer for our pets to have sequential anesthetic episodes, but it remains a small risk.
Finally, radiation therapy can cause cancer in patients, although rarely. While there are reports in both humans and animals of new cancers arising in areas of previous radiation treatment, overall the life-saving benefits of radiation therapy outweigh the risks.
Radiation therapy has come a long way in the last century, becoming safer and more effective. Veterinary oncologists have a powerful tool to fight cancer and improve the quality of life of pets and their families. Deciding whether radiation therapy is right for your dog is a team effort between you, your family veterinarian and a veterinary oncology specialist.