Radiation Therapy

Portrait young beauty dogProtecting the Normal Tissues, Written by Elias Gumpel

DVM, Chief Radiation Oncology Resident, www.gcvs.com
EXPERIENCE AND TECHNOLOGYRadiation therapy (RT) has become an integral component in veterinary cancer treatments over the past 20 years. In that relatively short period of time, the technology used for external beam radiation therapy (XRT) has progressed rapidly to the point where we are now able to localize tumors within a patient using a 3-dimensional imaging and planning system, perform treatment setups with minimal variations in the positioning of the patient, and protect the normal surrounding tissues in ways that were never before possible. By protecting the normal tissues better, there is less potential for side effects, which means a happier patient! Board certified veterinary radiation oncologists possess the necessary training and experience to utilize these technological advancements in order to achieve the best possible treatment outcome.

Most of us know someone that has undergone radiation treatments and we have seen the potential side effects of irradiation. Veterinary radiation oncologists minimize radiation side effects by adjusting the total radiation dose, varying the dose per treatment, and by customizing the treatment protocol to each patient. The hardware technology that is now available to deliver radiation treatments allows us to physically shape the beam of radiation to conform to the shape of the tumor, while the software planning technology gives us the ability to place limits, or restrictions, on how much dose is absorbed by critical organs that need to be spared from the primary radiation beam.

RADIATION SIDE EFFECTS

Radiation side effects in normal tissues occur to some degree with Protocol, but it is the severity of the reaction that varies. Radiation preferentially kills rapidly dividing cells because they spend more time in the radiation-sensitive phases of the cell cycle. Tumor cells are, by definition, rapidly dividing cells but there are also normal cells in the body that divide rapidly, such as bone marrow cells, skin cells and the cells that line the oral cavity and digestive tract. This is why patients that undergo irradiation will develop what are known as early side effects in these tissues if they are within the radiation field and receive sufficient dose. Fortunately, because these tissues have rapidly dividing cells, they are also able to heal relatively quickly, usually in a matter of 7-10 days. Late side effects occur in tissues whose cells do not divide rapidly, such as nervous system tissue, blood vessels, muscles, ligaments, tendons and bones. These side effects can be the most harmful and do not typically occur until months to years following irradiation. In veterinary medicine, current dosing techniques and equipment allow us to keep the risk of late side effects to less than 3%.

PROTECTING NORMAL TISSUES

Radiation therapy is the primary form of treatment for many tumors arising from the oral cavity, nasal cavity, brain, lungs, and in the pelvic region, but there are various normal structures in those areas that are at risk for both early and late radiation side effects. The use of a Multi-Leaf Collimator (MLC) with the linear accelerator (linac) allows us to shape the radiation beam to fit the shape of the tumor and spare those normal surrounding tissues of excessive and unnecessary exposure to radiation. Combining the MLC with Intensity Modulated Radiation Therapy (IMRT) 3D planning software allows us to place restrictions on the amount of radiation being delivered to the normal tissues while still delivering therapeutic doses to the tumor volume using state-of-the-art algorithms that generate multiple sub-segments per beam, each with a differently shaped opening through the MLC. This technology has drastically improved our ability to spare normal tissues and decrease both the incidence and severity of radiation side effects.

Learning that your pet has cancer is never easy, but your veterinary oncologist can play a vital role in providing valuable information regarding prognosis and treatment options to help to guide you through the process of determining the best way to manage and care for your pet. The oncologists at Gulf Coast Veterinary Specialists will work closely with your veterinarian to provide the best cancer care for your loved one.

Originally Published in the December 2010 Issue of Houston PetTalk Magazine.