Room: ePoster Forums
Purpose: The aim of this study was to determine the correlation of two normal tissue complication probability (NTCP) models and various dosimetric indices of the parotid glands with the patient reported severity of xerostomia 1 month after whole brain radiotherapy (WBRT).
Methods: 55 patients with complete treatment and follow-up data were eligible for analysis. Patients had adequate mental status and received WBRT (25-37.5 Gy in 10-15 fractions). Patient-reported outcome scores were collected based on the Michigan Xerostomia Questionnaire and a dry mouth Bother score. Patients completed questionnaires at baseline and 1 month post-WBRT. The clinical data were fitted by the Lyman-Kutcher-Burman (LKB) and Relative Seriality (RS) NTCP models.
Results: In this analysis, the two parotids were considered as a single structure. Median parotid mean dose was 17Gy (11-28Gy) and median parotid V20Gy was 48% (24-84%). The dose-volume indices in the rage V5Gy-V20Gy were found to correlate best with the follow-up data with their AUC values ranging between 0.68 and 0.71 for the two scoring systems. The values for the D50, m and n parameters of the LKB model were 22.3Gy, 0.84 and 1.0, respectively for the Michigan and 28.4Gy, 0.55 and 1.0 for the Bother scoring systems. Similarly, the values for the D50, Î³ and s parameters of the RS model were 23.5Gy, 0.28 and 0.0001 for the Michigan and 32.0Gy, 0.45 and 0.0001 for the Bother scores, respectively. Patients with parotid V20Gy â‰¥48% had 8.6 and 9.1 times higher xerostomia rate vs. <48% for the two scores, respectively.
Conclusion: Patient-reported xerostomia was found to be related with the dose metrics V5Gy-V20Gy. A threshold of V20Gy â‰¤ 49% was found to significantly reduce the risk for xerostomia. The dose-response curve of xerostomia could be determined by fitting the clinical data with the LKB and RS NTCP models.