2893 - Head and Neck Reirradiation with Stereotactic Ablative Radiotherapy: Predictors of Carotid Blow Out Syndrome

Purpose/Objective(s): This study aimed to identify factors that predict carotid blow out syndrome (CBOS) in recurrent head and neck (H&N) cancer patients treated with stereotactic ablative radiotherapy (SABR).

Materials/Methods: We retrospectively evaluated treatment charts and follow-up data from 191 patients treated at our clinic between 2007 and 2022. The study included patients who had previously received curative or adjuvant radiotherapy and underwent a second course of SABR with curative intent for local or regional recurrence. Acute and chronic toxicities were assessed using the CTCAE version 5. Predictors of CBOS were analyzed using univariate and multivariate logistic regression. Variables included age, gender (female vs. male), diagnosis (nasopharynx vs. other primaries), interval between RT courses, carotid artery encasement (<180° vs. =180°), pre-reirradiation salvage surgery (yes vs. no), reirradiation dose (EQD2), fractionation schedule (every other day vs. daily), treatment response (present vs. absent), gross tumor volume (GTV), maximum dose to the plan, and maximum dose to the carotid artery. Statistical significance was defined as p<0.05. All statistical analyses were performed using statistical software.

Results: CBOS occurred in 26 patients (13.6%), resulting in death for 19 patients (9%). The overall CBOS-related mortality rate was 9%, while mortality among patients who experienced CBOS was 73%. The median age was 47 years (range: 19-65), with 8 females (30.8%) and 18 males (69.2%). The primary tumor locations were the nasopharynx (16, 61.5%), larynx (3, 11.5%), hypopharynx (3, 11.5%), oral cavity (3, 11.5%), and an unknown primary (1, 3.8%). Most patients (18, 69.2%) received treatment every other day, while 8 (30.8%) received daily treatment. Tumor encasement of the carotid artery =180 degrees was observed in 22 patients (84%). The median tumor volume was 53.1 cc (range: 15-173 cc), and the median maximum dose to the carotid artery (Dmax) was 35.4 Gy (range: 0-43.1 Gy). The median time to CBOS after reirradiation was 7.9 months (range: 1.5-44.9 months), with 14 of 19 CBOS-related deaths occurring within the first year. Multivariate analysis identified age as a significant predictor of CBOS (p=0.02) and carotid artery encasement was borderline significant (p=0.08).

Conclusion: CBOS remains one of the most catastrophic side effects following the second course of irradiation, with a mortality rate of 73% in our cohort. However, its incidence in our nasopharyngeal cancer-dominant cohort is less than 15%. The risk of CBOS is particularly elevated in younger patients and in cases where the tumor encircles the carotid artery by more than 180 degrees. In such cases, implementing predictive measures and ensuring close follow-up—especially during the first year, when CBOS is most commonly observed—may help reduce mortality rates.