Cancer Veterinary Centers not only uses external beam radiation to treat our cancer patients but we can also use a very localized form of radiation called Plesiotherapy (the prefix plesio– is Greek for close or near). A strontium 90 applicator is a sealed source emitter that entails placement of a sealed radiation source in contact with the skin surface. The highest dose of radiation is deposited at the skin surface and the dose drops off rapidly with increased tissue depth (approximately 5% of the dose reaching deeper than 4 mm into the tissue). A single large bolus dose of radiation may be administered by direct application of the strontium 90 applicators to a superficially located tumor with minimal risk to underlying healthy tissues. One application field is used for small tumors, and several overlapping fields are used for lesions that exceed the width of the radiation source. The dose of radiation delivered depends on the interval of time during which the applicator is in contact with the skin. Strontium 90 irradiation has been used successfully to treat small superficial lesions (such as squamous cell carcinoma, mast cell tumors, melanoma) in dogs and cats. By having multiple forms of radiation therapy, we can offer multimodality treatment plans for our canine and feline patients.