Exhibit Hall | Forum 7
Purpose: To determine the values of two normal tissue complication probability (NTCP) models for the contralateral parotid and combination of contralateral parotid and submandibular glands regarding the endpoint of xerostomia based on the PRO-CTCAE scoring system, 12 months after radiotherapy for oropharynx cancer.
Methods: 204 patients with favorable risk, HPV-associated oropharyngeal squamous cell carcinoma were treated with radiotherapy. A dose of 60Gy delivered with IMRT was prescribed to the patients. Xerostomia was defined as a ≥2 point increase from baseline at 12 months post-RT. The dose volume histograms of the contralateral glands and contralateral parotid of each patient were exported. The clinical data was fitted by the Lyman-Kutcher-Burman (LKB) and Relative Seriality (RS) NTCP models.
Results: Xerostomia was observed in 39.2% and 13.8% of the patients in the PRO-QoL and CTCAE scoring systems. The values of the D50, m and n parameters of the LKB model for the PRO-QoL score were 51.6Gy, 1.04 and 0.18 for the contralateral glands and 38.4Gy, 1.31 and 0.38 for the contralateral parotid, respectively. The corresponding values of the D50, γ and s parameters of the RS model were 34.7Gy, 0.3 and 1.0 for the contralateral glands and 27.6Gy, 0.3 and 1.0 for the contralateral parotid, respectively. A statistically significant Odds Ratio (OR) of 2.7 was found for the contralateral glands for a gEUD threshold of 33Gy for the LKB model and 2.4 for gEUD = 22Gy for the contralateral parotid.
Conclusion: The LKB and RS NTCP models could fit the clinical data and determine the dose-response curve of contralateral glands and contralateral parotid regarding xerostomia based on the PRO-CTCAE score at 12 months post-RT. gEUD<33Gy and 22Gy to the contralateral glands and contralateral parotid was found to significantly reduce by 2.4-2.7 times the risk for radiation induced xerostomia.
NTCP, Radiation Effects, Modeling
TH- Response Assessment: Modeling: other than machine learning