Retrospective Quantitative Analysis Comparing Respiratory Gated to Non-respiratory Gated 18F-FDG PET/CT Imaging in Patients Undergoing Evaluation for Primary Lung Cancer.

1324 Objectives: In patients undergoing evaluation for primary lung cancer, 2-deoxy-2-(18F) fluoro-D-glucose (18F-FDG) positron emission tomography (PET)/computed tomography (CT) is a commonly used imaging examination for staging and treatment evaluation. Maximum and mean standardized uptake values (SUV) are commonly reported for these patients in practice, and metabolic tumor volume (MTV) and total lesion glycolysis (TLG) may have prognostic and treatment-related implications. Respiratory motion can result in displacement of lesions and degrade images of the lower chest in these patients, potentially reducing sensitivity of lesion detection and affecting the quantitative values that may have an effect on disease staging and treatment. We aim to assess the differences in quantitative values on non-respiratory gated versus respiratory gated FDG PET/CT imaging for discrete pulmonary lesions in patients undergoing evaluation for primary lung cancer. Methods: This study retrospectively reviewed 35 patients (13 males, 22 females, median age 69) evaluated for primary lung cancer with both non-respiratory gated and respiratory gated FDG PET/CT imaging obtained, including 36 separate FDG PET/CT exams and 49 discrete pulmonary lesions. Standard non-respiratory gated whole body FDG PET/CT was obtained at multiple bed positions (2 min each) except for sequentially obtained respiratory gated PET imaging at two bed positions (4 min each), encompassing the lower lung fields. An abdominal pressure sensor was used for respiratory cycle gating from peak inspiration to peak inspiration with data gathered from mid-expiration to mid-inspiration. The mean SUV (SUVmean) metabolic tumor volume (MTV41%), and total lesion glycolysis (TLG41%) were segmented using the software default adaptive threshold of 41% from the maximum in the volume of interest. SUVmax, SUVmean, MTV41%, and TLG41% were measured for each discrete pulmonary lesion on both non-respiratory gated and respiratory gated imaging utilizing automated software to calculate values within the volume of interest. Results: Data analysis demonstrates an increase in SUVmax in 81.6% of lesions, an increase in SUVmean in 87.7% of lesions, a decrease in MTV41% in 87.7% of lesions, and a decrease in TLG41% in 83.7% of lesions on respiratory gated FDG PET/CT imaging when compared to non-respiratory gated imaging. Utilizing a paired samples T-test, there was a significant difference between non-respiratory gated and respiratory gated imaging, respectively, for SUVmax (mean=8.5, SD=6.7 and mean=9.2, SD=6.8, p= Conclusions: Overall, respiratory gated FDG PET/CT imaging demonstrates a significant increase in SUVmax and SUVmean and a significant decrease in MTV and TLG when compared to non-respiratory gated PET/CT imaging in patients undergoing evaluation for primary lung cancer. The decrease in TLG with respiratory gated PET/CT imaging was an unexpected consequence. Further data analysis can evaluate the effect of lesion size, lesion location, and patient weight on these values.