Evaluation of the Accuracy of Standardized Uptake Values of ¹⁸F-fluorodeoxyglucose in Lung Lesions Based on Phantom...

The aim of the study was to estimate the accuracy of standardized uptake values of ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) in lung lesions during positron emission tomography combined with computed tomography (PET/CT) imaging, based on phantom studies performed for different PET/CT scanners.

The analysis of the PET/CT with ¹⁸F-FDG data was performed for 86 patients newly diagnosed with the lung lesions: malignant tumors (n=37), benign tumors and inflammatory diseases (n=49). The criteria for inclusion in the study were developed considering the recommendations of the Fleischner Society (2017). The characteristics of the lesions on CT met the following requirements: a round shape or close to it; total size of 8 to 30 mm; solid or subsolid structure (with the exception of lesion with ground-glass opacity); a solid part size of ≥8 mm. All the patients had no signs of pleurisy, lymphadenopathy, or cancer history. PET/CT imaging with ¹⁸F-FDG was performed with three scanners: Discovery 690 (General Electric, USA), Biograph mCT 128 (Siemens, Germany), and Biograph mCT 40 (Siemens); the preparation of patients prior to the scan was standardized. To determine the reference accumulation of a radiopharmaceutical in the pathological lesion, four scans of a specialized NEMA IEC PET Body Phantom Set (USA) were performed for each scanner. For each unit, the recovery coefficients (RCs) of radioactivity, maximum and recovered (corrected) standardized uptake values (SUVs) were determined. Statistical relationship between the size of lesions, SUV_max and SUV_correct was evaluated. Data processing was performed using MedCalc v. 19.2.0 software.

During the phantom study, the underestimation of the radioactivity was determined in the spheres with the diameters of 10 and 13 mm, overestimation was observed in the sphere with the diameter of 28 mm. Both underestimation and overestimation of radioactivity were determined for the spheres with a diameter of 17 and 22 mm.SUV_max differed from the reference values for 85 patients (98.8%). The underestimation of these values was found for 63 patients (73.2%) due to the partial volume effect. The greatest underestimation was observed for the patients with 8 mm diameter lesions. Depending on the scanner, the underestimation of the SUV_max in these patients reached up to 54-73%. For 9 patients (25%) with malignant tumors of 9-12 mm, the utility of RC made it possible to avoid false negative results. For the lesions with a diameter of 30 mm, an overestimation of SUV_max up to 22% was determined due to the negative influence of the reconstruction algorithms.

The use of RC eliminates the influence of the partial volume effect and reconstruction methods on the accuracy of estimating the SUV_max in lung lesions, which ensures reproducibility, increase in the information content of the method, as well as the comparability of the results of PET/CT with ¹⁸F-FDG obtained on the different models of PET/CT units with different technological characteristics.