Room: Davidson Ballroom A
Purpose: To identify the sections of the pharyngeal constrictors that best correlate with the clinical endpoint of dysphagia. To determine the dosimetric metrics that correlate well with the outcome data. Based on two toxicity scoring systems, to estimate the parameters of two NTCP models that describe the dose-response relation of dysphagia.
Methods: This study involves eighty-three patients with favorable risk, HPV-associated oropharyngeal squamous cell carcinoma, who were treated on a prospective multi-institutional phase II study. All patients received 60Gy IMRT and they reported toxicity using two scoring systems (CTCAE-PRO and QLQ-C30). Dysphagia was defined as a â‰¥ 2 point increase from baseline (pre-RT value) and was assessed at 12 months post-RT. The individual patient dosimetric data of the superior, medium and inferior pharyngeal constrictors (SPC, MPC, IPC) as separate structures as well as combinations were derived. The clinical data were fitted by the Lyman-Kutcher-Burman (LKB) and Relative Seriality (RS) NTCP models.
Results: For the CTCAE-PRO system, the AUC values were highest for the SPC (Dmean and V52: 0.86 and 0.82, respectively) and combined constrictors (Dmean and V59: 0.81 and 0.79, respectively). The values for the QLQ-C30 were Dmean and V55: 0.62 and 0.65, respectively for the SPC, whereas for the combined constrictors they were 0.52 and 0.61 for Dmean and V55, respectively. The calculated parameters of the LKB model were D50 = 63.4Gy, m = 0.10, n = 1.0 for the SPC, whereas for the RS model they were D50 = 61.2Gy, Î³ = 5.37, s = 0.0001.
Conclusion: A correlation was established between the mean dose and given dose volume metrics with dysphagia, which was stronger for the CTCAE-PRO system. The examined NTCP models could fit the clinical data well with similar accuracy. The SPC appear to correlate best with the outcome data from the CTCAE-PRO and QLQ-C30 systems.