2055 - Dose-Response Modeling of Dysphagia Toxicities for Head and Neck SBRT Re-Irradiation

Purpose/Objective(s): Re-irradiation (re-RT) is a viable treatment strategy for recurrent head and neck cancer (HNC), but the risk of normal tissue toxicity remains significant. This study quantifies the risk of re-RT-induced dysphagia in patients with loco-regionally recurrent HNC who were re-irradiated with curative intent Stereotactic Body Radiotherapy (SBRT).

Materials/Methods: Dose-volume data from 33 HNC patients who underwent a second course of SBRT (18–35 Gy [median: 30 Gy] in 2–5 fractions [median: 4]) were retrospectively reviewed. Toxicity outcomes, assessed using CTCAE criteria, were analyzed for 13 patients who developed late grade = 2 dysphagia, including 3 patients with grade 3 dysphagia. To account for variations in fractionation, the spatial dose distributions were converted to equivalent dose in 2 Gy fractions (EQD2) and summed volumetrically. Probit modeling with maximum log-likelihood optimization was used to evaluate normal tissue complication probability (NTCP) as a function of mean and maximum dose to the larynx and supraglottic larynx.

Results: The most common diagnosis was squamous cell carcinoma (80%), with 52% of patients receiving systemic therapy. The median follow-up was 3–6 months, and the median interval between the first and second irradiation was 32 months (range: 4–84 months). The risk of dysphagia correlated more strongly with dose to the supraglottic larynx than to the larynx. The supraglottic larynx mean dose resulting in a 50% complication probability (D50) was 53 Gy [68% CI: 41–72 Gy], with a normalized dose-response gradient (?50) of 0.96 [68% CI: 0.64–1.71]. The D50 for the supraglottic larynx maximum dose was 84 Gy [68% CI: 75–96 Gy]. For the larynx, the mean and maximum dose D50 values were 39 Gy [68% CI: 30–52 Gy] and 71 Gy [68% CI: 59–100 Gy], respectively, with ?50 values of 0.99 [68% CI: 0.7–1.79] and 0.82 [68% CI: 0.56–1.89].

Conclusion: Our findings suggest that a supraglottic larynx mean EQD2 dose of <53 Gy and a maximum EQD2 dose of <84 Gy in 2–5 fractions during re-irradiation are associated with a <50% risk of grade = 2 dysphagia. These dose constraints should be carefully considered in patients with recurrent HNC undergoing SBRT to minimize toxicity.