Non-Irradiation-Related Complications in Cats Undergoing Radiation Therapy: A Single-Institution Retrospective Study...

The incidence of non-irradiation-related complications in cats receiving radiotherapy has not been previously reported. Medical records of 167 cats treated with radiotherapy under general anesthesia at a single institution (2002-2025) were reviewed. Head/neck tumors were most common (n = 119). Ninety-two cats (55%) received short-course radiotherapy (1-8 fractions, median 4), and 75 cats (45%) received longer course radiotherapy (10-19 fractions, median 16). Median treatment duration spanned 16 calendar days (range, 1-35). Complications resolving without intervention or requiring outpatient treatment were categorized as mild, and those requiring hospitalization for supportive care or discontinuation of radiation therapy (RT) were considered severe. Mild anesthesia-related complications occurred in 72 cats (43%), whereas mild non-anesthesia-related complications occurred in 30 cats (18%). Three cats (2%) experienced treatment delays due to mild complications. Preexisting hypertensive chronic kidney disease (p = 0.0201) and vasopressor use (p = 0.0001) were associated with mild anesthesia-related complications on multivariate analysis. Severe complications requiring hospitalization occurred in 19 cats (11%), including gastrointestinal, fever, anemia, neurologic, renal, cardiac, endocrine, and ocular events; treatment was delayed in 7 (4%) and discontinued in 12 (7%) of these cats. Weight loss from the start to end of treatment (p = 0.016) was associated with severe complications on multivariate analysis, with 40% of cats losing >5% of body weight during treatment. As the hematocrit decreased by >5% in 27% of cats, recheck after RT is recommended. Six cats (4%) were euthanized during radiotherapy due to tumor progression (n = 3) or severe complications (n = 3). Overall, 11% of cats experienced severe non-irradiation-related complications that rarely led to death.