Predictive Capability and Dynamic Characteristic of Tumor Voxel Dose-Response Assessed Using 18F-FDG PET/CT Imaging Feedback

Abstract

To effectively implement FDG-PET/CT imaging feedback for tumor voxel treatment response assessment and treatment adaptation, this study investigated the predictive capability and the dynamic characteristic of tumor voxel treatment response with respect to the timing of imaging feedback.Serial FDG-PET/CT images were obtained at pretreatment and weekly during the standard chemoradiotherapy with treatment dose of 2Gy × 35 from 33 head and neck cancer patients. Reference of tumor voxel dose-response matrix (DRMref) was constructed for each patient using the average slope of tumor voxel PET intensity change ratio obtained from the first 4 weekly PET feedback images following deformable PET/CT image registration. The predictive capability of tumor voxel DRM assessed using 1 or 2 PET feedback images obtained during the first 4 treatment weeks was evaluated. The evaluation included the tumor voxel DRM correlation and the voxel DRM discrepancy between the predictions and the reference. The dynamic characteristics of DRM were studied by comparing the DRM assessed at different treatment weeks. The dynamic characteristics were also correlated to the tumor volume and tumor voxel location with respect to the human papillomavirus (HPV) status.The correlation coefficient between the DRMref and the DRMs predicted using a single feedback image increased from 0.82±0.2 for DRM2 at the 2nd treatment week to 0.95±0.03 for DRM4 at the 4th treatment week. The deviation between the tumor voxel DRMref and the predicted DRMs was (4.7±53.9)% for DRM2, (-7.3±21.1)% for DRM3, and (6.2±15.6)% for DRM4. The deviation reduced to (4.4±8.4)% or (1.1±7.8)% when using the week 2&4 or 3&4 feedback images. Tumor voxel improved its response significantly after 2nd treatment week in both HPV+ and HPV- tumors. In HPV- tumors, the magnitude of tumor voxel DRM reduction was correlated with the distance from the tumor surface to the voxels with a Spearman correlation coefficient = 1, P = 0.017.Tumor voxel treatment response showed large improvement after the 2nd treatment week with the delivered dose of 2Gy × 10 and got relatively stabilized after 2Gy × 15. FDG-PET/CT imaging acquired in the 3rd treatment week is recommended if single image feedback is selected. Feedback images obtained in the 2nd and 4th treatment weeks will additionally improve predictive capability and provide guidance for early treatment dose adjustment.