Room: Exhibit Hall | Forum 7
Purpose: To determine the dose-response relation of pharyngeal constrictors regarding the endpoint of patient reported severity of dysphagia 12 months after radiotherapy for oropharynx cancer. Additionally, to correlated various dosimetric indices of the pharyngeal constrictors with this symptom and identify risk thresholds.
Methods: 120 patients with HPV-associated oropharyngeal squamous cell carcinoma were treated with 60Gy IMRT with concurrent weekly chemotherapy. Dysphagia was assessed based on the PRO-CTCAE score and more specifically it was defined at 12 months post-RT as a â‰¥ 2 point increase from baseline. Individual patient dosimetric data from the superior (SPC) and combined pharyngeal constrictors were correlated with dysphagia. The clinical data was fitted by two normal tissue complication probability (NTCP) models, namely the Lyman-Kutcher-Burman (LKB) and Relative Seriality (RS) models.
Results: Dysphagia was observed in 13 patients (11%). For SPC the dose-volume index V50Gy and mean dose were found to correlate with the symptom (AUC value for both was 0.76). The corresponding AUC value for the combined constrictors was 0.69 for V60Gy and mean dose. For SPC, the values of the D50, m and n parameters of the LKB model were 65.3Gy, 0.10 and 1.0, whereas the values of the D50, Î³ and s parameters of the RS model were 65.4Gy, 3.14 and 0.0001. A statistically significant Odds Ratio of 10.3 (95%CI: 1.8-57.9) and 9.5 (95%CI: 1.2-73.9) was found for the SPC and combined constrictors at gEUD â‰¤ 61Gy and gEUD â‰¤ 58Gy, respectively.
Conclusion: The LKB and RS NTCP models could fit the clinical data and determine the dose-response curve of SPC and combined constrictors regarding dysphagia. gEUD â‰¤ 61Gy to SPC and gEUD â‰¤ 58Gy to the combined constrictors were found to significantly reduce the risk for patient reported dysphagia. Also, V50Gy to SPC and V60Gy to the combined constrictors were correlated with dysphagia.