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

Purpose: Tumor voxel dose-response matrix (DRM) can be quantified using feedback from serial FDG-PET/CT imaging acquired during radiotherapy. This study investigated the dynamic characteristics and the predictive capability of DRM. Methods: FDG-PET/CT images were acquired before and weekly during standard chemoradiotherapy with the treatment dose 2 Gy x 35 from 31 head and neck cancer patients. For each patient, deformable image registration was performed between the pretreatment/baseline PET/CT image and each weekly PET/CT image. Tumor voxel DRM was derived using linear regression on the logarithm of the weekly standard uptake value (SUV) ratios for each tumor voxel, such as SUV measured at a dose level normalized to the baseline SUV0. The dynamic characteristics were evaluated by comparing the DRM; estimated using a single feedback image acquired at the ith treatment week (i =1, 2, 3, or 4) to the DRM estimated using the last feedback image for each patient. The predictive capability of the DRM estimated using 1 or 2 feedback images was evaluated using the receiver operating characteristic test with respect to the treatment outcome of tumor local-regional control or failure. Results: The mean +/- SD of tumor voxel SUV measured at the pretreatment and the 1st, 2nd, 3rd, 4th, and last treatment weeks was 6.76 +/- 3.69, 5.72 +/- 3.43, 3.85 +/- 2.22, 3.27 +/- 2.25, 2.5 +/- 1.79, and 2.23 +/- 1.27, respectively. The deviations between the DRM; estimated using the single feedback image obtained at the ith week and the last feedback image were 0.86 +/- 4.87, -0.06 +/- 0.3, -0.09 +/- 0.17, and -0.09 +/- 0.12 for DRM1, DRM2, DRM3, and DRM4, respectively. The predictive capability of DRM3 and DRM4 was significant (p < 0.001). The area under the curve (AUC) was increased with the increase in treatment dose level. The DRMs constructed using the single feedback image achieved an AUC of 0.86 similar to 1. The AUC was slightly improved to 0.94 similar to 1 for the DRMs estimated using 2 feedback images. Conclusion: Tumor voxel metabolic activity measured using FDG-PET/CT fluctuated noticeably during the first 2 treatment weeks and obtained a stabilized reduction rate thereafter. Tumor voxel DRM constructed using a single FDG-PET/CT feedback image after the 2nd treatment week (>20 Gy) has a good predictive capability. The predictive capability improved continuously using a later feedback image and marginally improved when two feedback images were applied.

Automated summary

This study investigated the dynamic characteristics and predictive capability of tumor voxel dose-response matrix (DRM) using feedback from serial FDG-PET/CT imaging during radiotherapy. The results showed that DRM constructed using a single FDG-PET/CT feedback image after the 2nd treatment week has good predictive capability, and the predictive capability improves continuously using a later feedback image and slightly improves when two feedback images are applied.