Incidence of arterial and venous vascular complications after radiotherapy for head and neck cancer: A systematic review and meta-analysis.

e18104 Background: Advances in radiotherapy (RT) have improved locoregional control and survival in head and neck cancer (HNC). Long-term vascular toxicity is a clinically important yet underrecognized late effect. This is the first meta-analysis to systematically quantify the incidence of radiation-associated vascular toxicity using only primary studies, stratified by mode of detection and duration of follow-up. Methods: We searched MEDLINE, Embase, and Cochrane (inception-Jan 2025) databases. A meta-analysis of proportions using random-effects models was performed, stratified by detection method (screening vs. clinical) and follow-up (≤5 years, >5 years). Only primary observational studies were included in the quantitative synthesis. Results: A meta-analysis of 12 observational studies (n=2,682) was performed using a random-effects model. The pooled incidence of screening-detected carotid stenosis (≥50%) was 28.3% (95% CI: 21.5–35.7), significantly higher than the 9.4% (95% CI: 6.2–13.3) incidence of clinically-detected stroke/TIA—a 3.0-fold difference. Subgroup analysis revealed a strong time-dependent relationship: incidence was 7.5% within 5 years post-RT but escalated to 32.1% beyond 5 years. Venous complications (jugular thrombosis/stenosis) were sparsely reported (2-5% incidence in 2 studies). Statistical heterogeneity was high across all analyses (I² > 80%). Meta-analysis revealed a 28.3% incidence of screening-detected carotid stenosis (≥50%) versus 9.4% for clinical stroke/TIA—a 3.0-fold disparity. Incidence rose progressively from 7.5% (<5 years) to 32.1% (>5 years) post-RT. Conclusions: Based on primary data, vascular complications represent a substantial under-recognized survivorship burden. Screening-detected disease is three times more prevalent than clinically apparent disease. The marked escalation in risk beyond 5 years post-RT justifies consideration of targeted surveillance for high-risk, long-term survivors.