68 Ga-PSMA-PET/CT for the evaluation of pulmonary metastases and opacities in patients with prostate cancer

Abstract

BackgroundThe purpose of this study was to investigate the imaging properties of pulmonary metastases and benign opacities in 68Ga-PSMA positron emission tomography (PET) in patients with prostate cancer (PC).Methods68Ga-PSMA-PET/CT scans of 739 PC patients available in our database were evaluated retrospectively for lung metastases and non-solid focal pulmonary opacities. Maximum standardized uptake values (SUVmax) were assessed by two- and three-dimensional regions of interest (2D/3D ROI). Additionally CT features of the lesions, such as location, morphology and size were identified.ResultsNinety-one pulmonary metastases and fourteen opacities were identified in 34 PC patients. In total, 66 PSMA-positive (72.5%) and 25 PSMA-negative (27.5%) metastases were identified. The mean SUVmax of pulmonary opacities was 2.2±0.7 in 2D ROI and 2.4±0.8 in 3D ROI. The mean SUVmax of PSMA-positive pulmonary metastases was 4.5±2.7 in 2D ROI and in 4.7±2.9 in 3D ROI; this was significantly higher than the SUVmax of pulmonary opacities in both 2D and 3D ROI (p<0.001). The mean SUVmax of PSMA-negative metastases was 1.0±0.5 in 2D ROI and 1.0±0.4 in 3D ROI, and significantly lower than that of the pulmonary opacities (p<0.001). A significant (p<0.05) weak linear correlation between size and 3D SUVmax in lung metastases (ρSpearman=0.207) was found.ConclusionBased on the SUVmax in 68Ga-PSMA-PET alone, it was not possible to differentiate between pulmonary metastases and pulmonary opacities. The majority of lung metastases highly overexpressed PSMA, while a relevant number of metastases were PSMA-negative. Pulmonary opacities demonstrated a moderate tracer uptake, significantly lower than PSMA-positive lung metastases, yet significantly higher than PSMA-negative metastases.

Comparison of 3 Interpretation Criteria for 68Ga-PSMA11 PET Based on Inter- and Intrareader Agreement

“…Particularly, lung nodules appear to lead not only to interreader but also intercriteria disagreement (equivocal vs. negative) in the PET/CT group. Although lung metastases from PC are relatively rare (16,17), small lung nodules can often be problematic in interpretation. Compared with PSMA-RADS, EANM and PROMISE criteria have a greater emphasis on the existence of PSMA uptake.…”

“…That is, EANM and PROMISE criteria generally regard lesions without elevated PSMA uptake as negative findings (9,10), whereas PSMA-RADS can include such lesions in the equivocal criteria (PSMA-RADS-3D) (11). When applying these criteria, one should keep in mind that small lesions such as lung nodules can be falsely judged as negative because of the partial-volume effect (17). However, this problem can be solved by clearly stating information on PSMAnegative lesions in the interpretation report, regardless of the criteria used.…”

PSMA Theranostics: Review of the Current Status of PSMA-Targeted Imaging and Radioligand Therapy

“…Preclinical research has suggested that despite an overall increase in PSMA expression during progression of PCa from androgen sensitivity to androgen independence, some metastatic cell lines lose PSMA expression [ 75 ]. A significant proportion of liver metastases may also lack PSMA expression, although most liver metastases highly overexpress PSMA [ 76 ]. Heterogeneity of PSMA expression may partly explain why about 30% of patients do not respond to 177 Lu-PSMA RLT [ 77 ].…”

68Ga-PSMA Uptake in Pulmonary Tuberculosis: A Pitfall in Prostate Cancer PET Imaging

“…In our case, pulmonary tuberculosis shows mild 68 Ga-PSMA uptake, which is similar to the most lung benign diseases with mild to moderate PSMA expression. In addition, most PSMA-positive lung malignant diseases demonstrate intense PSMA uptake, and the SUVmax is relatively higher than benign diseases [3,4]. Thus, the SUVmax may be of differential significance for most PSMA-positive lung lesions.…”