Relationship between radiation dose and cerebral microbleed formation in dogs with intracranial tumors.

Abstract

BACKGROUND: Cerebral microbleeds (CMBs) are a possible sequela in human brain tumor patients treated with radiation therapy (RT). No such association is reported in dogs. OBJECTIVES: To investigate whether CMBs occur in dogs after radiotherapy, and if there is an association between number and dose, and an increase over time. ANIMALS: Thirty-four client-owned dogs irradiated for primary intracranial neoplasia. &#x2265;2 magnetic resonance imaging (MRI) scans including susceptibility-weighted imaging (SWI) were required. METHODS: Retrospective, observational, single-center study. Cerebral microbleeds identified on 3&#x2009;T SWI were counted within the entire brain, and within low- (<20&#x2009;Gy), intermediate- (20-30&#x2009;Gy), and high- (>30&#x2009;Gy) dose regions. A generalized linear mixed-effects model was used to analyze the relationship between the CMBs count and the predictor variables (irradiation dose, time after treatment). RESULTS: Median follow-up time was 12.6&#x2009;months (range, 1.8-37.6&#x2009;months). Eighty-three MR scans were performed. In 4/15 dogs (27%, 95% CI, 10%-52%) CMBs were present at baseline. &#x2265;1 CMBs after RT were identified in 21/34 dogs (62%, 95% CI, 45%-77%). With each month, the number of CMBs increased by 14% (95% CI, 11%-16%; P&#x2009;<&#x2009;.001). The odds of developing CMBs in the high-dose region are 4.7 times (95% CI, 3.9-5.6; P&#x2009;<&#x2009;.001) greater compared with the low-dose region. CONCLUSION AND CLINICAL IMPORTANCE: RT is 1 possible cause of CMBs formation in dogs. Cerebral microbleeds are most likely to occur in the peritumoral high-dose volume, to be chronic, and to increase in number over time. Their clinical relevance remains unknown.