Tumor Treatment Response Assessed During the Chemo-Radiotherapy for Locally Advanced NSCLC.

PURPOSE/OBJECTIVE(S): To evaluate the capability of assessing intratumoral treatment response distribution with using FDG-PET/CT during the chemoradiotherapy of locally advanced NSCLC.

MATERIALS/METHODS: Twelve of total 50 patients with stage III NSCLC were enrolled in the institutional protocol for concurrent chemoradiotherapy with treatment dose of 54-60 Gy in 27-30 fractions. For each patient, a pre-treatment FDG-PET/CT image (SUV0 ) and a mid-treatment image (SUVm ) obtained within the treatment dose of 24 ∼ 46 Gy were obtained. Followed by deformable PET/CT registration between SUV0 and SUVm , the tumor voxel SUV reduction ratio was obtained to construct a tumor dose response matrix (DRM). Tumor SUVavid was also constructed by limiting tumor voxel SUVm > a given value. Spatial correlations of the tumor SUV0 , SUVm , SUVavid and DRM were determined.

RESULTS: The mean and coefficient variation (CV) of the SUV0 , SUVm and DRM for all tumors were 6.56(64%), 2.82(59%) and 0.52(70%) (Table contains the individual data), which were like those on the SUVs and the mean DRM of head-neck HPV- patients reported previously, but much larger on the DRM variation. The inter-tumoral CVs of SUV0 and DRM were 17% and 43%, which were much smaller than those of the intra-tumoral CVs 61% and 55%. Meanwhile, the intra-tumoral variations on both SUV0 and DRM were much larger than those of head-neck HPV- patients. There was a weak correlation between SUV0 and SUVm with the correlation coefficient 0.32, a medium correlation of -0.51 between SUV0 and DRM; 0.58 between SUVm and DRM. It implies that the rule of tumor dose response DRM on treatment modification decision cannot be fully replaced by either SUV0 or SUVm . The spatial correlation between tumor DRM and SUVavid was 0.23 with SUVavid value > 3, which was getting weaker when increasing SUVavid value.

CONCLUSION: Spatial dose response for NSCLC assessed using FDG-PET/CT feedback demonstrated high treatment resistant patterns, which had a large intra-tumoral variation. In addition, the medium correlations of DRM vs SUV0 and DRM vs SUVm imply that all these factors could be used to guide adaptive modification of NSCLC treatment.