Normalized Uptake Fraction: An Alternative for Metabolic Quantification

Abstract

Introduction: Functional imaging with 18F-FDG PET/CT has become a valuable tool in Oncology. Standardized uptake value represents a semi-quantitative approach in PET in order to have an easy way to evaluate tissues metabolic rate. Despite the recommendations for its inclusion in clinical reports, its calculation is affected by multiple variables making difficult to compare exams from different labs or to use it in radiotherapy planning. Our goal was the development of an alternative methodology of quantification that despite remaining semiquantitative is less operator's dependent. Material and methods:We studied 32 women with cervical cancer in stage IIB, IIIA and IIIB that were scanned with 18 F-FDG PET/CT previously to treatment. Additionally, one woman had an evaluation post treatment, and another one was also evaluated 25 months after treatment terminus. Images were included in Velocity AI ® and the results of an independent and blind evaluation by two experts including the contouring of gross tumor volume were compared. Images were also included in MEVISLAB ® platform, an image processing and visualization software, and we obtained parametric images of the distribution of, what we called, normalized uptake fraction (FCN). Visualization of the FCN images was lower bounded by taking into account the activity of quadriceps muscle. Representative clinical cases were selected to describe our image results. Results and conclusion:We obtained an independent visualization method, allowing a new approach in quantification of metabolic imaging. There is evidence that, through visual navigation in CT-mode but mainly in PET/CT-mode after application of FCN, we were allowed to analyze quantification images of PET/CT, from different patients and different equipment's, without the controversial ROI or VOI definition and measurement of respective SUV. For radiotherapy planning the proposed method seems to improve the determination of biological target volume (BTV).