Factors predicting metastatic disease in 68Ga-PSMA-11 PET positive osseous lesions in prostate cancer.

Bone is the most common site of distant metastatic spread in prostate adenocarcinoma. Prostate-specific membrane antigen uptake has been described in both benign and malignant bone lesions, which can lead to false-positive findings on 68Ga-prostate-specific membrane antigen-11 positron emission tomography (68Ga-PSMA-11 PET). The purpose of this study was to evaluate the diagnostic accuracy of 68Ga-PSMA-11 PET for osseous prostate cancer metastases and improve bone uptake interpretation using semi-quantitative metrics. METHODS: 56 prostate cancer patients (18 pre-prostatectomy, 38 biochemical recurrence) who underwent 68Ga-PSMA-11 PET/MRI or PET/CT examinations with osseous PSMA-ligand uptake were included in the study. Medical records were reviewed retrospectively by board-certified nuclear radiologists to determine true or false positivity based on a composite endpoint. For each avid osseous lesion, biological volume, size, PSMA-RADS rating, maximum standardized uptake value (SUVmax), and ratio of lesion SUVmax to liver, blood pool, and background bone SUVmax were measured. Differences between benign and malignant lesions were evaluated for statistical significance, and cut-off values for these parameters were determined to maximize diagnostic accuracy. RESULTS: Among 56 participants, 13 patients (22.8%) had false-positive osseous 68Ga-PSMA-11 findings and 43 patients (76.8%) had true-positive osseous 68Ga-PSMA-11 findings. Twenty-two patients (39%) had 1 osseous lesion, 18 (32%) had 2-4 lesions, and 16 (29%) had 5 or more lesions. Cut-off values resulting in statistically significant (p<0.005) differences between benign and malignant lesions were: PSMA-RADS ≥4, SUVmax ≥4.1, SUVmax ratio of lesion to blood pool ≥2.11, to liver ≥0.55, and to bone ≥4.4. These measurements corresponded to lesion-based 68Ga-PSMA-11 PET lesion detection rate for malignancy of 80%, 93%, 89%, 21%, 89%, and a specificity of 73%, 73%, 73%, 93%, 60%, respectively. CONCLUSION: PSMA-RADS rating, SUVmax, and SUVmax ratio of lesion to blood pool can help differentiate benign from malignant lesions on 68Ga-PSMA-11 PET. SUVmax ratio to blood pool above 2.2 is a reasonable parameter to support image interpretation and presented superior lesion detection rate and specificity when compared to visual interpretation by PSMA RADS. These parameters hold clinical value by improving diagnostic accuracy for metastatic prostate cancer on 68Ga-PSMA-11 PET/MRI and PET/CT.

Journal of nuclear medicine : official publication, Society of Nuclear Medicine. 2020 Apr 17 [Epub ahead of print]

Le Wen Chiu, Courtney Lawhn-Heath, Spencer Behr, Roxanna Juarez, Paola M Perez, Iryna Lobach, Matthew D Bucknor, Thomas A Hope, Robert R Flavell

University of California, San Francisco, United States.