Initial Experience with Volumetric (68)Ga-PSMA I&T PET/CT for Assessment of Whole-body Tumor Burden as a Quantitative Imaging Biomarker in Patients with Prostate Cancer

A quantitative imaging biomarker is desirable to provide a comprehensive measure of whole-body tumor burden in patients with metastatic prostate cancer, and to standardize the evaluation of treatment-related changes. Therefore, we evaluated whether prostate specific membrane antigen (PSMA) ligand positron emission tomography/computed tomography (PET/CT) may be applied to provide PSMA-derived volumetric parameters for quantification of whole-body tumor burden. Methods: 101 patients who underwent a (68)Ga-PSMA I&T PET/CT because of increasing prostate specific antigen (PSA) levels after radical prostatectomy were included in this retrospective analysis. Tracer uptake was quantified using standardized uptake values (SUVs). Volumetric parameters, i.e. PSMA-derived tumor volume (PSMA-TV) and total lesion PSMA (TL-PSMA) were calculated for each patient using a three-dimensional segmentation and computerized volumetry technique, and compared with serum PSA levels. In a group of 10 patients, volumetric parameters were applied for treatment monitoring. Results: Volumetric parameters, i.e. whole-body PSMA-TV and whole-body TL-PSMA, demonstrated a statistically significant correlation with PSA levels (P < 0.0001) as a surrogate marker of tumor burden, whereas SUVmax (P = 0.22) or SUVmean (P = 0.45) did not. Treatment response and treatment failure were paralleled by concordant changes in both whole-body PSMA-TV and whole-body TL-PSMA (P = 0.02), whereas neither the change in SUVmax (P = 1.0) nor SUVmean (P = 1.0) concordantly paralleled changes in PSA levels. Conclusion: PSMA-derived volumetric parameters provide a quantitative imaging biomarker for whole-body tumor burden, capable of standardizing quantitative changes in PET imaging of patients with metastatic prostate cancer, and of facilitating therapy monitoring.

Journal of nuclear medicine : official publication, Society of Nuclear Medicine. 2017 May 18 [Epub ahead of print]

Sebastian Schmuck, Christoph A von Klot, Christoph Henkenberens, Jan M Sohns, Hans Christiansen, Hans-Jürgen Wester, Tobias L Ross, Frank M Bengel, Thorsten Derlin

Hannover Medical School, Germany., Technische Universitaet Muenchen, Germany.