Variations in ¹⁸F-FDG uptake in breast cancer depending on PET/CT acquisition position

Aim To evaluate the variability of quantitative 2-[¹⁸F]-fluoro-2-deoxy-d-glucose (FDG) positron-emission tomography (PET) combined with computed tomography (CT) parameters depending on acquisition position in a dual-position protocol for breast cancers. Materials and methods For initial staging work-up, whole-body PET/CT was first acquired in a supine position, and then followed by a regional breast scan in a prone position. The maximum standardised uptake value (SUV_max), metabolic tumour volume (MTV), and total lesion glycolysis (TLG) were measured on both acquisition positions. MTV₅₀ and TLG₅₀ were calculated with a threshold set to be 50% of SUV_max, and MTV_2.5 and TLG_2.5 with a fixed SUV threshold of 2.5. Results The median SUV_max of breast cancers measured on the supine scans was 4.88, and 4.49 on the prone images (p<0.05). MTV and TLG also yielded significantly lower values from supine images. Regarding the tendency for the acquisition position to yield different results, a significant disagreement was observed between SUV_max and MTV₅₀ and between SUV_max and TLG₅₀ (kappa = -0156 and -0.001, respectively), while MTV_2.5 and TLG_2.5 showed a fair to moderate agreement with SUV_max (kappa = 0.311 and 0.416, respectively). Conclusions SUV_max, MTV, and TLG yielded lower values when acquired in the prone position compared to in the supine position. This observation could be due to the partial volume effect. When using 50% of SUV_max as a threshold, there was a significant discordance between SUV_max and volumetric parameters. Thus, acquisition position may affect quantitative PET/CT parameters and the clinical implications.