Room: Exhibit Hall
Purpose: Quantifying therapeutic induced intra-tumoral FDG uptake changes at the image voxel level requires deformable image registration (DIR) performed between pairwise PET/CT images. This study aims to investigate the DIR algorithmsâ€™ performance on registering sequential PET/CT images obtained from a human head-and-neck cancer xenografts tumor undergoing radiotherapy.
Methods: Xenografts were established in 15 nude NIH III mice by injecting UT-SCC-14 cells subcutaneously into the flank. The mice were irradiated by delivery with 2Gy/day and 5days/week. 18F-FDG micro-PET/CT scans were performed before treatment and after 10Gy and 20Gy of dose delivery with a reconstructed PET/CT image voxel size 0.5x0.5x0.6/0.15x0.15x0.15mmÂ³. Tumor was manually delineated on PET/CT scans. Weekly PET/CT images were aligned manually to their pre-treatment PET/CT images based on the tumor contours. An image intensity based DIR (IM-DIR) and a biomechanical based DIR (BM-DIR) were performed respectively between each weekly CT and its pre-treatment CT images using the tumor contours as constraints or boundary conditions. The transformations were applied to deform weekly PET images to their pre-treatment images. The Jacobian and the standard uptake value (SUV) obtained using the two DIRs were compared. To test the effect of tumor volume changes on the registration discrepancy, Spearmanâ€™s correlation was performed between the tumor volume changes and the average SUV absolute differences from the two DIRs.
Results: Tumor volume increased by (39.84Â±17.2)% after 20Gy of dose delivery. The Jacobian values were 1.28Â±0.73 and 1.28Â±0.47 for the IM-DIR and BM-DIR. The displacement-vector-difference between the two DIRs was (0.39Â±0.33)mm and the SUV absolute difference was (7.4Â±9.02)%. The correlation between the tumor volume changes and the tumor voxel SUV discrepancies was not significant (p=0.107).
Conclusion: The BM-DIR produced more physical plausible transformations with less voxels have extreme Jacobian values. The tumor voxel SUV discrepancies caused by the two DIRs were uncorrelated to the tumor volume changes.