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

TLDR

A quantitative imaging biomarker is needed to comprehensively measure whole‑body tumor burden in metastatic prostate cancer and standardize treatment‑related evaluations. The study assessed whether PSMA‑ligand PET/CT could yield volumetric parameters to quantify whole‑body tumor burden. In a retrospective cohort of 101 patients with rising PSA after prostatectomy, PSMA‑derived tumor volume (PSMA‑TV) and total lesion PSMA (TL‑PSMA) were calculated by 3‑D segmentation and compared to PSA levels, with a subset of 10 patients used for treatment monitoring. PSMA‑TV and TL‑PSMA correlated strongly with PSA (P<0.0001) and tracked treatment response, whereas SUV metrics did not, demonstrating that PSMA‑derived volumetrics are a quantitative biomarker for whole‑body tumor burden and therapy monitoring.

Abstract

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 PET/CT may be applied to provide PSMA-derived volumetric parameters for quantification of whole-body tumor burden. <b>Methods:</b> One hundred one patients who underwent ⁶⁸Ga-PSMA I&amp;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 SUVs. Volumetric parameters, that is, PSMA-derived tumor volume (PSMA-TV) and total lesion PSMA (TL-PSMA), were calculated for each patient using a 3-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. <b>Results:</b> Volumetric parameters, that is, whole-body PSMA-TV and whole-body TL-PSMA, demonstrated a statistically significant correlation with PSA levels (<i>P</i> &lt; 0.0001) as a surrogate marker of tumor burden, whereas SUV_max (<i>P</i> = 0.22) or SUV_mean (<i>P</i> = 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 (<i>P</i> = 0.02), whereas neither the change in SUV_max (<i>P</i> = 1.0) nor the change in SUV_mean (<i>P</i> = 1.0) concordantly paralleled changes in PSA levels. <b>Conclusion:</b> 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.