These data do not support the broad application of FDG-PET/CT for radiation response assessment in unselected head and neck cancer patients. However, FDG-PET/CT may be the imaging modality of choice for patients with highest risk disease, particularly those with HPV-negative tumors. Optimal timing of FDG-PET/CT imaging after radiotherapy merits further investigation.

Purpose Xerostomia is a major complication of head and neck radiotherapy. Available xerostomia measures remain flawed. FDG-PET/CT is routinely used for staging and response assessment of head and neck cancer. We investigated quantitative measurement of parotid gland FDG uptake as a potential biomarker for post-radiotherapy xerostomia. Methods and Materials Ninety-eight locally advanced head and neck cancer patients receiving definitive radiotherapy underwent baseline and post-radiotherapy FDG-PET/CT on a prospective imaging trial. A separate validation cohort of 14 patients underwent identical imaging while prospectively enrolled onto a second trial collecting sialometry and patient-reported outcomes. Radiation dose and pre/post-RT SUVs for all voxels contained within parotid gland regions-of-interest were deformably registered. Results Average whole gland or voxel-by-voxel models incorporating parotid DMet (defined as the pre-treatment parotid SUV weighted by dose) accurately predicted post-treatment changes in parotid FDG uptake (e.g. fractional parotid SUV). Fractional loss of parotid FDG uptake closely paralleled early parotid toxicity defined by post-treatment salivary output (p < 0.01) and RTOG/EORTC xerostomia scores (p < 0.01). Conclusions In this pilot series, loss of parotid FDG uptake strongly associates with acute clinical post-radiotherapy parotid toxicity. DMet may potentially be used to guide function-sparing treatment planning. Prospective validation of FDG-PET/CT as a convenient, quantifiable imaging biomarker of parotid function is warranted and ongoing.

Purpose-The optimal roles for imaging-based biomarkers in the management of head and neck cancer remain undefined. Unresolved questions include whether functional or anatomic imaging biomarkers might improve mortality risk assessment for this disease. We addressed these issues in a prospective institutional trial.Methods and Materials-Ninety-eight patients with locally advanced pharyngolaryngeal squamous cell cancer were enrolled. Each underwent pre-and post-chemoradiotherapy contrastenhanced CT and FDG-PET/CT imaging. Imaging parameters were correlated with survival outcomes.Results-Low post-radiation primary tumor FDG avidity correlated with improved survival on multivariate analysis; so too did complete primary tumor response by CT alone. Although both imaging modalities lacked sensitivity, each had high specificity and negative predictive value for disease-specific mortality risk assessment. Kaplan-Meier estimates confirmed that both CT and

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