To correlate carotid dose and risk of carotid blowout syndrome (CBOS) after stereotactic body radiation therapy (SBRT), hypothesizing that carotid dose does not correlate with CBOS.

We retrospectively reviewed 186 patients with recurrent, previously irradiated head and neck cancer treated between January 2008 and March 2013. Patients treated early in our experience with incomplete dosimetry were excluded from analysis (n = 111). A total of 75 patients were identified, providing 150 carotid arteries for analysis. Median follow-up was 8 months (range, 1-91 months) for all patients, and 37 months for surviving patients (range, 31-91 months). Patients were treated with linear accelerator-based SBRT to a median dose up to 44 Gy (range, 40-50 Gy) in 5 fractions delivered on a twice-weekly basis. Concurrent cetuximab was used in 63 patients (84%). The bilateral common, internal, and external carotid arteries were delineated 2 cm above and below the planning target volume. The maximum dose to 0.1 cm (D), 1 cm (D), and 2 cm (D) of the carotid and the mean carotid dose from SBRT were recorded and analyzed for association with carotid bleeding events, using binary logistic regression.

Median reirradiation interval was 20 months (range, 3-423 months), and median prior radiation dose was 70 Gy (range, 52.5-140 Gy). Sixteen patients (21.3%) received more than 1 course of SBRT, and the cumulative carotid doses from fused summary plans were recorded. The overall median D D D, and mean carotid doses were 40.8 Gy (interquartile range [IQR], 21.6-47.6 Gy), 26.8 Gy (IQR, 14.1-42.1 Gy), 15.4 Gy (IQR, 8.4-32.7 Gy), and 15.0 Gy (IQR, 8.9-23.3 Gy), respectively. There were a total of 4 bleeding events (5.3%): 2 patients (2.7%) had mucosal bleeds that resolved after embolization of carotid branches, and 2 patients (2.7%) died from complications of CBOS. In the 2 patients with CBOS the D was 48.4 Gy and 47.6 Gy, respectively. There was no significant association between bleeding events and D (P = .280), D (P = .571), or mean dose (P = .568). There was a trend toward increased risk of bleeding and D (P = .080).

These results demonstrate a low risk of bleeding after reirradiation with SBRT when 5 fractions are delivered on nonconsecutive days, even when tumor is completely encasing the carotid artery. Although limited by the low number of events, no significant association was found between dose-volume parameters and the risk of carotid bleeding. No CBOS was noted when D was <47.6 Gy.