3631 - Clinical Parameters Associated with Carotid Artery Stenosis and Stroke Following Neck Radiotherapy

S. DSilva¹, M. Lin², D. Pinkham³, J. Doherty⁴, C. Nguyen⁴, K. Wijesooriya⁵, and C. McLaughlin³; ¹University of Virginia, Department of Radiation Oncology, Charlottesville, VA, ²University of Virginia School of Medicine, Charlottesville, VA, ³Department of Radiation Oncology, University of Virginia, Charlottesville, VA, ⁴Department of Physics, University of Virginia, Charlottesville, VA, ⁵University of Virginia, Department of Radiation Oncology, Department of Physics, Charlottesville, VA

Purpose/Objective(s): While vasculopathies are a known complication of radiation therapy, the exact mechanism and dose-dependency of damage are not fully understood. Several published studies have tried to identify a relationship between carotid artery radiation dose and subsequent stenosis, but dosimetric parameters predictive of this outcome remain unclear. The purpose of this study is to generate hypotheses about the relationship between clinical factors and risk of carotid stenosis and carotid events (TIA and CVA) in patients who received radiotherapy to the neck. Materials/

Methods: A retrospective case-control study was performed, by identifying patients who had received head and neck RT and subsequently underwent screening carotid ultrasounds. Of these patients, those with carotid stenosis on post-RT ultrasounds were compared to patients without stenosis. Data from the cohort were analyzed to assess the association between clinical and carotid dosimetric variables and carotid stenosis severity as well as the occurrence of carotid events. Logistic regression was employed to explore factors contributing to carotid events, while linear regression was used to evaluate severity scores. Univariate and multivariate analyses were conducted to identify significant predictors.
Results: Among the patients who had carotid stenosis post RT, only a small proportion experienced carotid events (7/43). No dosimetric variables (max carotid dose, mean carotid dose, dose to relative and absolute volumes of carotid) were correlated with carotid events or carotid stenosis severity. Logistic regression revealed age as the sole statistically significant variable associated with carotid events (p = 0.02). For severity scores, univariate analyses identified several significant predictors: patient age was significantly correlated with left- and right-sided carotid stenosis severity after RT (p = 0.001 and 0.02 respectively), but pre-existing carotid artery calcifications on either side of the neck were significantly correlated with only the severity of left-sided stenosis after RT, via linear regression (r = 0.44 for calcifications on the left side (p = 0.05) vs r = 0.57 for the right (p = 0.01)).
Conclusion: These findings suggest that patient age prior to neck RT may increase the risk of carotid events, whereas pre-existing calcifications are associated with the severity of carotid stenosis on the left side. Previous studies have shown that left carotids have a higher prevalence of intraplaque hemorrhage than the right; further research is needed to clarify possible mechanisms of the asymmetrical impact of prior calcifications on post-RT carotid stenosis. While we did not identify any dosimetric variables associated with post-RT carotid stenosis or carotid events, clinical factors such as age and pre-existing calcifications may help identify patients at risk, and could be used to tailor surveillance.