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Comparison of Tumor Volumes Derived from Glucose Metabolic Rate Maps and SUV Maps in Dynamic ¹⁸F-FDG PET

¹ Department of Nuclear Medicine, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands; and ² Department of Radiation Oncology, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands

Correspondence: For correspondence contact: Eric P. Visser, Department of Nuclear Medicine (internal postal code 444), Radboud University Nijmegen Medical Centre, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands. E-mail: e.visser{at}nucmed.umcn.nl

Tumor delineation using noninvasive medical imaging modalities is important to determine the target volume in radiation treatment planning and to evaluate treatment response. It is expected that combined use of CT and functional information from ¹⁸F-FDG PET will improve tumor delineation. However, until now, tumor delineation using PET has been based on static images of ¹⁸F-FDG standardized uptake values (SUVs). ¹⁸F-FDG uptake depends not only on tumor physiology but also on blood supply, distribution volume, and competitive uptake processes in other tissues. Moreover, ¹⁸F-FDG uptake in tumor tissue and in surrounding healthy tissue depends on the time after injection. Therefore, it is expected that the glucose metabolic rate (MR_glu) derived from dynamic PET scans gives a better representation of the tumor activity than does SUV. The aim of this study was to determine tumor volumes in MR_glu maps and to compare them with the values from SUV maps. Methods: Twenty-nine lesions in 16 dynamic ¹⁸F-FDG PET scans in 13 patients with non–small cell lung carcinoma were analyzed. MR_glu values were calculated on a voxel-by-voxel basis using the standard 2-compartment ¹⁸F-FDG model with trapping in the linear approximation (Patlak analysis). The blood input function was obtained by arterial sampling. Tumor volumes were determined in SUV maps of the last time frame and in MR_glu maps using 3-dimensional isocontours at 50% of the maximum SUV and the maximum MR_glu, respectively. Results: Tumor volumes based on SUV contouring ranged from 1.31 to 52.16 cm³, with a median of 8.57 cm³. Volumes based on MR_glu ranged from 0.95 to 37.29 cm³, with a median of 3.14 cm³. For all lesions, the MR_glu volumes were significantly smaller than the SUV volumes. The percentage differences (defined as 100% x (V_MRglu – V_SUV)/V_SUV, where V is volume) ranged from –12.8% to –84.8%, with a median of –32.8%. Conclusion: Tumor volumes from MR_glu maps were significantly smaller than SUV-based volumes. These findings can be of importance for PET-based radiotherapy planning and therapy response monitoring.

Key Words: dynamic PET • FDG • SUV • glucose metabolic rate • NSCLC

COPYRIGHT © 2008 by the Society of Nuclear Medicine, Inc.

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