Kerner G.S.M.A., Fischer A., Koole M.J.B., Pruim J., Groen H.J.M.
University of Groningen and Department of Pulmonary Diseases, University Medical Center Groningen, Hanzeplein 1, P.O. Box 30.001,, Groningen, Netherlands; Philips Technologie GmbH Innovative Technologies, Postfach 40, Philipstr. 8, Aachen, Germany; University of Groningen and Department of Nuclear Medicine and Molecular Imaging, University Medical Center Groningen, Hanzeplein 1, P.O. Box 30.001,, Groningen, Netherlands; Department of Nuclear Medicine, Tygerberg Hospital, Stellenbosch University, Francie van Zijl drive, Cape Town, South Africa
Kerner, G.S.M.A., University of Groningen and Department of Pulmonary Diseases, University Medical Center Groningen, Hanzeplein 1, P.O. Box 30.001,, Groningen, Netherlands; Fischer, A., Philips Technologie GmbH Innovative Technologies, Postfach 40, Philipstr. 8, Aachen, Germany; Koole, M.J.B., University of Groningen and Department of Nuclear Medicine and Molecular Imaging, University Medical Center Groningen, Hanzeplein 1, P.O. Box 30.001,, Groningen, Netherlands; Pruim, J., University of Groningen and Department of Nuclear Medicine and Molecular Imaging, University Medical Center Groningen, Hanzeplein 1, P.O. Box 30.001,, Groningen, Netherlands, Department of Nuclear Medicine, Tygerberg Hospital, Stellenbosch University, Francie van Zijl drive, Cape Town, South Africa; Groen, H.J.M., University of Groningen and Department of Pulmonary Diseases, University Medical Center Groningen, Hanzeplein 1, P.O. Box 30.001,, Groningen, Netherlands
Background: Deformable image registration allows volume of interest (VOI)- and voxel-based analysis of longitudinal changes in fluorodeoxyglucose (FDG) tumor uptake in patients with non-small cell lung cancer (NSCLC). This study evaluates the performance of the elastix toolbox deformable image registration algorithm for VOI and voxel-wise assessment of longitudinal variations in FDG tumor uptake in NSCLC patients. Methods: Evaluation of the elastix toolbox was performed using 18F-FDG PET/CT at baseline and after 2 cycles of therapy (follow-up) data in advanced NSCLC patients. The elastix toolbox, an integrated part of the IMALYTICS workstation, was used to apply a CT-based non-linear image registration of follow-up PET/CT data using the baseline PET/CT data as reference. Lesion statistics were compared to assess the impact on therapy response assessment. Next, CT-based deformable image registration was performed anew on the deformed follow-up PET/CT data using the original follow-up PET/CT data as reference, yielding a realigned follow-up PET dataset. Performance was evaluated by determining the correlation coefficient between original and realigned follow-up PET datasets. The intra- and extra-thoracic tumors were automatically delineated on the original PET using a 41% of maximum standardized uptake value (SUVmax) adaptive threshold. Equivalence between reference and realigned images was tested (determining 95% range of the difference) and estimating the percentage of voxel values that fell within that range. Results: Thirty-nine patients with 191 tumor lesions were included. In 37/39 and 12/39 patients, respectively, thoracic and non-thoracic lesions were evaluable for response assessment. Using the EORTC/SUVmax-based criteria, 5/37 patients had a discordant response of thoracic, and 2/12 a discordant response of non-thoracic lesions between the reference and the realigned image. FDG uptake values of corresponding tumor voxels in the original and realigned reference PET correlated well (R2=0.98). Using equivalence testing, 94% of all the voxel values fell within the 95% range of the difference between original and realigned reference PET. Conclusions: The elastix toolbox impacts lesion statistics and therefore therapy response assessment in a clinically significant way. The elastix toolbox is therefore not applicable in its current form and/or standard settings for PET response evaluation. Further optimization and validation of this technique is necessary prior to clinical implementation. © 2015, Kerner et al.; licensee Springer.