PT - JOURNAL ARTICLE AU - Marie Bieth AU - Markus Krönke AU - Robert Tauber AU - Marielena Dahlbender AU - Margitta Retz AU - Stephan G. Nekolla AU - Bjoern Menze AU - Tobias Maurer AU - Matthias Eiber AU - Markus Schwaiger TI - Exploring New Multimodal Quantitative Imaging Indices for the Assessment of Osseous Tumor Burden in Prostate Cancer Using <sup>68</sup>Ga-PSMA PET/CT AID - 10.2967/jnumed.116.189050 DP - 2017 Oct 01 TA - Journal of Nuclear Medicine PG - 1632--1637 VI - 58 IP - 10 4099 - http://jnm.snmjournals.org/content/58/10/1632.short 4100 - http://jnm.snmjournals.org/content/58/10/1632.full SO - J Nucl Med2017 Oct 01; 58 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 &lt; 0.001) and prostate-specific antigen values (r = 0.57 and 0.54, respectively, P &lt; 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.