High detection performance and accurate staging of adrenal glands using state-of-the-art PET/CT

Objectives To determine the performance of a state-of-the-art Positron Emission Tomography/Computed Tomography (PET/CT) system in the detection and staging of adrenal glands in patients with suspected lung cancer.

Methods We included 79 consecutive patients with suspected lung cancer, who underwent fluorodeoxyglucose (FDG) PET/CT using a novel time-of-flight system (Ingenuity TF, Philips Healthcare). One experienced observer assessed the adrenal gland visibility by viewing PET/CT. Adrenal glands that were not visualized were regarded as ‘undetectable’. Literature reports a detection percentage of 68% [1]. For 30 adrenal glands, we obtained cytological/histological information and calculated the maximum standardized-uptake-value (SUVmax) and the ratio between adrenal gland and liver FDG-uptake (AL-ratio). The optimal cut-off values to distinguish benign from malignant glands were considered to be the values with the highest accuracy. Findings were compared with literature where cut-off values of 2.5 for SUVmax and 1.0 for AL-ratio [2-4] are generally considered typical.

Results Adrenal uptake was frequently seen on PET-only images. In combination with CT, the adrenal glands were detected in 99% of the cases. SUVmax values for benign (n=14) and malignant (n=16) glands were 2.8±0.5 (mean±SD) and 7.4±2.6, respectively (p<0.01). The corresponding AL-ratios were 1.3±0.3 and 3.3±1.3, respectively (p<0.01). Optimal cut-off values for SUVmax and AL-ratio were 4.0 (with accuracy 97%) and 1.9 (accuracy 83%), respectively.

Conclusions The detection performance of adrenal glands using state-of-the-art PET/CT is excellent (99% detected). For accurate distinction between malignant and benign adrenal glands, higher cut-off values for SUVmax and AL-ratio should be used than reported in the literature. Readers and referring physicians should update their cut-off levels when implementing new PET technology.