Non‐Irradiation‐Related Complications in Cats Undergoing Radiation Therapy: A Single‐Institution Retrospective Study of 167 Cats (2002–2025)

ABSTRACT

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.