RT Journal Article SR Electronic T1 Exploring New Multimodal Quantitative Imaging Indices for the Assessment of Osseous Tumor Burden in Prostate Cancer Using 68Ga-PSMA PET/CT JF Journal of Nuclear Medicine JO J Nucl Med FD Society of Nuclear Medicine SP 1632 OP 1637 DO 10.2967/jnumed.116.189050 VO 58 IS 10 A1 Marie Bieth A1 Markus Krönke A1 Robert Tauber A1 Marielena Dahlbender A1 Margitta Retz A1 Stephan G. Nekolla A1 Bjoern Menze A1 Tobias Maurer A1 Matthias Eiber A1 Markus Schwaiger YR 2017 UL http://jnm.snmjournals.org/content/58/10/1632.abstract AB PET combined with CT and prostate-specific membrane antigen (PSMA) ligands has gained significant interest for staging prostate cancer (PC). In this study, we propose 2 multimodal quantitative indices as imaging biomarkers for the assessment of osseous tumor burden using 68Ga-PSMA PET/CT and present preliminary clinical data. Methods: We defined 2 bone PET indices (BPIs) that incorporate anatomic information from CT and functional information from 68Ga-PSMA PET: BPIVOL is the percentage of bone volume affected by tumor and BPISUV additionally considers the level of PSMA expression. We describe a semiautomatic computation method based on segmentation of bones in CT and of lesions in PET. Data from 45 patients with castration-resistant PC and bone metastases during 223Ra-dichloride were retrospectively analyzed. We evaluated the computational stability and reproducibility of the proposed indices and explored their relation to the prostate-specific antigen blood value, the bone scan index (BSI), and disease classification using PERCIST. Results: On the technical side, BPIVOL and BPISUV showed an interobserver maximum difference of 3.5%, and their computation took only a few minutes. On the clinical side, BPIVOL and BPISUV showed significant correlations with BSI (r = 0.76 and 0.74, respectively, P < 0.001) and prostate-specific antigen values (r = 0.57 and 0.54, respectively, P < 0.01). When the proposed indices were compared against expert rating using PERCIST, BPIVOL and BPISUV showed better agreement than BSI, indicating their potential for objective response evaluation. Conclusion: We propose the evaluation of BPIVOL and BPISUV as imaging biomarkers for 68Ga-PSMA PET/CT in a prospective study exploring their potential for outcome prediction in patients with bone metastases from PC.