Weight changes and gamma radiation emissions during the three-week isolation period following administration of radioactive iodine (I131) in cats with hyperthyroidism

Abstract

Hyperthyroidism is the most common endocrine disorder seen in cats and is frequently associated with weight loss. Following treatment weight gain should be seen and therefore weight assessment should form part of the monitoring protocol for cats with this condition. Although several treatment options are available for hyperthyroidism in cats, radioactive iodine (I131) is the gold standard treatment for this condition. I131 is offered by several institutions within the United Kingdom (UK); however, this treatment is associated with variable hospitalization periods due to the radiation hazards that these cats pose to their owners following treatment. Hospitalization length and costs associated with this treatment have both been found to have a negative impact on the frequency that I131 is offered and utilized by general practitioners and owners respectively. The aims of the studies presented in this thesis were to assess the weight changes of hyperthyroid cats seen during the three-week isolation period following I131 administration and assess if an electronic personal dosimeter (EPD) could be used to document the levels of gamma (γ) radiation emitted from treated cats during the same time period. For the study assessing the weight changes in treated cats, weight changes were shown to be useful as an indicator of the reversal of biochemical hyperthyroidism; however, factors including the gender and age of the cat were not found to affect the weight changes that occurred. For the γ radiation emission study, it was also assessed whether the current 21-day hospitalization period at the Small Animal Hospital (SAH) could be shortened. It was shown that an EPD can be used to measure the γ radiation emitted from treated cats and that a reduction of the current isolation period to 14 days is possible in cats treated with ≤ 200 megabecquerels (MBq) of I131. Both of these studies have added to our knowledge and understanding of I131 treatment in cats and have demonstrated the merits of using weight changes in the assessment of treatment of hyperthyroidism and the utility of EPDs for measuring γ radiation emissions in treated cats

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