Dose-response analysis of parotid gland function: What is the best measure of xerostomia?

Purpose: To describe the dose-response relationships for the different measures of salivary gland recovery following radical radiotherapy for locally advanced-head and neck squamous cell cancers (LA-HNSCC). Methods and materials: Dosimetric analysis of data from the PARSPORT trial, a Phase III study of conventional RT (RT) and intensity modulated radiotherapy (IMRT) for LA-HNSCC was undertaken to determine the relationship between parotid gland mean dose and toxicity endpoints: high-grade subjective and objective xerostomia and xerostomia-related quality of life scores. LKB-NTCP parameters (TD50, m and n) were generated and tolerance doses (D50) reported using non-linear logistic regression analysis. Results: Data were available on 63 patients from the PARSPORT trial. Parotid saliva flow rate provided the strongest association between mean dose and recovery, D50 = 23.4 Gy (20.6-26.2) and k = 3.2 (1.9-4.5), R-2 = 0.85. Corresponding LKB parameters were TD50 = 26.3 Gy (95% CI: 24.0-30.1), m = 0.25 (0.18-1.0 and n = 1). LENTSOMA subjective xerostomia also demonstrated a strong association D50 = 33.3 Gy (26.7-39.8), k = 2.8 (91.4-4.4), R-2 = 0.77). Conclusion: We recommend using the LENT SOMA subjective xerostomia score to predict recovery of salivation due to its strong association with dosimetry and ease of recording. (C) 2013 Elsevier Ireland Ltd. All rights reserved.