Using Nuclear Medicine to Diagnose and Treat Cancer in Cats and Dogs

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Selting K.

Conference Proceedings, (2016). American College of Veterinary Internal Medicine, Denver:

 

INTRODUCTION

The use of radioactive iodine to treat hyperthyroid cats has become common over the past 20 years. Administration is minimally invasive, the therapy spares the parathyroid glands, and licensing to handle and administer such small doses is readily obtained. Many private specialty practices provide this service. The concept of using radiation (energy) to treat abnormal tissue has many other applications, and identification of appropriate patients for referral can increase options for diagnosis and treatment.

A rapidly expanding armamentarium of isotopes will change veterinary cancer care. Radioisotopes such as 18F- fluorodeoxy glucose (18F-FDG) can exploit the metabolism of the cancer cell, allowing improved and minimally invasive staging, as well as the ability to locate an elusive pathologic process. Additionally, by using inherent and manufactured targeting characteristics, and by selecting the desired energy for a biologic effect, radioisotopes can be used to target the cancer cell while sparing normal tissue. In veterinary medicine, facilities that work with radioactive diagnostic and therapeutic isotopes are sparse, and the goal of this talk is to inform the listener of the appropriate applications for nuclear medicine for veterinary patients. This discussion will help identify cases for which referral to a facility with nuclear medicine will be beneficial.

External beam radiation therapy has been the mainstay of radiation therapy for many years. This entails fractionated treatments over the course of approximately 3–6 weeks. The use of cross sectional imaging (CT scans) for computer- guided planning allows relative sparing of normal tissue and targeting of tumor tissue. Brachytherapy involves implanting a radioactive source into the tumor, and the energy that is emitted is highly concentrated around the point sources, resulting in sometimes complete sparing of the surrounding normal tissue. However, proper orientation of sources can be challenging. Brachytherapy can also be accomplished using targeted pharmaceuticals such as radioiodine and samarium. The University of Missouri houses the largest research reactor on a university campus in North America, and the active radiopharmaceutical program offers unique opportunities for research and clinical treatment of animals with cancer.