Geometric Image Biomarker Changes of the Parotid Gland Are Associated With Late Xerostomia.

PURPOSE: To identify a surrogate marker for late xerostomia 12 months after radiation therapy (Xer12m ), according to information obtained shortly after treatment.

METHODS AND MATERIALS: Differences in parotid gland (PG) were quantified in image biomarkers (ΔIBMs) before and 6 weeks after radiation therapy in 107 patients. By performing stepwise forward selection, ΔIBMs that were associated with Xer12m were selected. Subsequently other variables, such as PG dose and acute xerostomia scores, were added to improve the prediction performance. All models were internally validated.

RESULTS: Prediction of Xer12m based on PG surface reduction (ΔPG-surface) was good (area under the receiver operating characteristic curve, 0.82). Parotid gland dose was related to ΔPG-surface (P<.001, R2  = 0.27). The addition of acute xerostomia scores to the ΔPG-surface improved the prediction of Xer12m significantly, and vice versa. The final model including ΔPG-surface and acute xerostomia had outstanding performance in predicting Xer12m early after radiation therapy (area under the receiver operating characteristic curve, 0.90).

CONCLUSIONS: Parotid gland surface reduction was associated with late xerostomia. The early posttreatment model with ΔPG-surface and acute xerostomia scores can be considered as a surrogate marker for late xerostomia.