Abstract

Purpose: To test a short 2-[18F]Fluoro-2-deoxy-D-glucose (2-[18F]FDG) PET dynamic acquisition protocol to calculate Ki using regional Patlak graphical analysis in patients with non-small-cell lung cancer (NSCLC).Methods: 24 patients with NSCLC who underwent standard dynamic 2-[18F]FDG acquisitions (60 min) were randomly divided into two groups. In group 1 (n = 10), a population-based image-derived input function (pIDIF) was built using a monoexponential trend (10–60 min), and a leave-one-out cross-validation (LOOCV) method was performed to validate the pIDIF model. In group 2 (n = 14), Ki was obtained by standard regional Patlak plot analysis using IDIF (0–60 min) and tissue response (10–60 min) curves from the volume of interests (VOIs) placed on descending thoracic aorta and tumor tissue, respectively. Moreover, with our method, the Patlak analysis was performed to obtain Ki,s using IDIFFitted curve obtained from PET counts (0–10 min) followed by monoexponential coefficients of pIDIF (10–60 min) and tissue response curve obtained from PET counts at 10 min and between 40 and 60 min, simulating two short dynamic acquisitions. Both IDIF and IDIFFitted curves were modeled to assume the value of 2-[18F]FDG plasma activity measured in the venous blood sampling performed at 45 min in each patient. Spearman's rank correlation, coefficient of determination, and Passing–Bablok regression were used for the comparison between Ki and Ki,s. Finally, Ki,s was obtained with our method in a separate group of patients (group 3, n = 8) that perform two short dynamic acquisitions.Results: Population-based image-derived input function (10–60 min) was modeled with a monoexponential curve with the following fitted parameters obtained in group 1: a = 9.684, b = 16.410, and c = 0.068 min−1. The LOOCV error was 0.4%. In patients of group 2, the mean values of Ki and Ki,s were 0.0442 ± 0.0302 and 0.33 ± 0.0298, respectively (R2 = 0.9970). The Passing–Bablok regression for comparison between Ki and Ki,s showed a slope of 0.992 (95% CI: 0.94–1.06) and intercept value of −0.0003 (95% CI: −0.0033–0.0011).Conclusions: Despite several practical limitations, like the need to position the patient twice and to perform two CT scans, our method contemplates two short 2-[18F]FDG dynamic acquisitions, a population-based input function model, and a late venous blood sample to obtain robust and personalized input function and tissue response curves and to provide reliable regional Ki estimation.

Highlights

  • The 2-[18F]Fluoro-2-deoxy-D-glucose (2-[18F]FDG) Positron Emission Tomography/Computed Tomography (PET/CT) is a well-established imaging modality for staging, restaging, and monitoring treatment response in patients with malignancy [1,2,3]

  • Absolute quantification of 2-[18F]FDG concentration, related to the local metabolic rate of glucose consumption measured with full kinetic analysis of time-activity curves, has proven to better characterize the tumor cell behavior and to correlate with histopathological data and prognosis [4,5,6]

  • It has shown that the accuracy of standard uptake value (SUV) depends on several factors, including the standardization of technical parameters, which can affect the reliability of uptake values [10,11,12,13]

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Summary

Introduction

The 2-[18F]Fluoro-2-deoxy-D-glucose (2-[18F]FDG) Positron Emission Tomography/Computed Tomography (PET/CT) is a well-established imaging modality for staging, restaging, and monitoring treatment response in patients with malignancy [1,2,3]. Some key points of full kinetic analysis, mainly the long dynamic acquisition and arterial blood sampling, limit the use of such an approach in a clinical setting For these reasons, less-invasive approaches, including measurements of semiquantitative parameters such as the most common standard uptake value (SUV), are extensively used routinely [7,8,9]. The Ki parameter is calculated from the slope of a straight line that correlates the integral radioligand activity in the blood pool with radioligand activity in the tissue [15] For this purpose, a long PET dynamic acquisition lasting at least 60 min is considered mandatory to calculate the time-activity curves of 2-[18F]FDG in the blood (input function) and tissue (tissue response). Several efforts have been made to simplify the input function estimation with less- or non-invasive methods, such as the arterialized venous blood sampling [16], the image-derived input function (IDIF) estimation [17,18,19,20], the population input function modeling [21,22,23,24], the image segmentation methods [25, 26], and to overcome difficulties related to the long-lasting dynamic acquisition [27,28,29,30]

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