Carotid Dosimetry and the Risk of Carotid Blowout Syndrome Following Re-irradiation with Head and Neck Stereotactic Body Radiation Therapy

Publication date: Available online 5 December 2017
Source:International Journal of Radiation Oncology*Biology*Physics
Author(s): Brian J. Gebhardt, John A. Vargo, Diane Ling, Brianna Jones, Mary Mohney, David A. Clump, James P. Ohr, Robert L. Ferris, Dwight E. Heron
Background/PurposeStereotactic Body Radiation Therapy (SBRT) is an increasingly used technique for re-irradiation of recurrent head-and-neck cancers (rHNC). Rates of carotid blowout syndrome (CBOS), which is defined as rupture and hemorrhage from the carotid artery or its major branches following re-irradiation in the absence of residual or progressive disease, have varied from 0-17% occurring at a median of 4-5 months following SBRT. This has prompted some to aggressively spare the carotids or avoid SBRT in patients with arterial encasement. Our institutional practice has not excluded patients from SBRT based on extent of carotid involvement or carotid dose. Thus, we aimed to correlate carotid dose and risk of CBOS; hypothesizing that carotid dose does not correlate with CBOS.Methods/MaterialsWe 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) for all patients, and 37 months for surviving patients (range: 31-91]. Patients were treated with linear accelerator-based SBRT to a median dose up to 44Gy (range: 40-50 Gy) in 5 fractions delivered on a twice-weekly basis. Concurrent Cetuximab was utilized in 63 patients (84%). The bilateral common, internal, and external carotid arteries were delineated 2cm above and below the planning target volume. The maximum dose to 0.1cc (D0.1cc), 1cc (D1cc), 2cc (D2cc) of the carotid and the mean carotid dose from SBRT were recorded and analyzed for association with carotid bleeding events using binary logistic regression.ResultsMedian re-irradiation interval was 20 months (range: 3-423), median prior radiation dose was 70 Gy (range: 52.5-140). 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 D0.1cc, D1cc, D2cc, and mean carotid doses were 40.8 Gy [interquartile range (IQR): 21.6-47.6], 26.8 Gy [IQR: 14.1-42.1], 15.4 Gy [IQR: 8.4-32.7], and 15.0 Gy [IQR: 8.9-23.3], respectively. There were a total of 4 bleeding events (5.3%): 2 patients (2.7%) had mucosal bleeds that resolved following embolization of carotid branches, and 2 patients (2.7%) died from complications of CBOS. In the 2 patients suffering CBOS, the D0.1cc were 48.4 Gy and 47.6 Gy. There was no significant association between bleeding events and D1cc (p=0.280), D2cc (p=0.571), or mean dose (p=0.568). There was a trend toward increased risk of bleeding and D0.1cc (p=0.080).ConclusionsThese results demonstrate a low risk of bleeding following re-irradiation with SBRT when 5 fractions are delivered on non-consecutive days even when tumor is completely encasing the carotid artery. While limited by low number of events, no significant association was found between dose-volume parameters and the risk of carotid bleeding. No CBOS noted when D0.1cc was <47.6 Gy.

Teaser

Stereotactic body radiation therapy has emerged as a viable treatment option for recurrent head and neck cancers after prior irradiation, though carotid dose constraints are not defined. The maximum dose to 0.1cc, 1cc, 2cc of the carotid and the mean dose were analyzed for association with bleeding. No significant association was found between dose-volume parameters and risk of carotid bleeding, and no CBOS noted when D0.1cc was <47.6 Gy.


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