RT Journal Article SR Electronic T1 Lu177 PSMA Radioligand Therapy: In vivo SPECT/CT quantitation JF Journal of Nuclear Medicine JO J Nucl Med FD Society of Nuclear Medicine SP 668 OP 668 VO 58 IS supplement 1 A1 Zohar Keidar A1 Rachel Lugassi A1 Elyahu Raysberg A1 Alex Frenkel A1 John Kennedy A1 Ora Israel YR 2017 UL http://jnm.snmjournals.org/content/58/supplement_1/668.abstract AB 668Objectives: 177LuPSMA (LuP) is a novel approach in radioligand targeted therapy for metastatic prostate cancer. Dosimetry, based on measurement of the radioligand concentration, is critical to achieve optimal therapeutic effect in malignant sites with limited exposure of healthy organs. Few currently available quantitative methods for in-vivo measurement of radiopharmaceutical uptake involve multiple time points imaging and blood samples. Current study aims at validating a new imaging-based quantitation software for in-vivo/in-vitro correlation of LuP activity in the urinary bladder of prostate cancer patients (pts).Methods: Six patients underwent 10 treatment cycles (4 x one cycle, 1 x two and 1 x three cycles) after administration of 3-5 GBq LuP. Whole body SPECT/CT was performed at 4, 24 and 48/72 hours after each treatment cycle using general purpose device equipped with CZT detector. A urinary sample was collected following each SPECT/CT acquisition and measured for radioactivity in a well counter. Quantitative measurement of uptake in the urinary bladder on each SPECT/CT study was performed with the Q.Metrix® software (Xeleris, GE Healthcare) utilizing semi-automatic 3D segmentation tools. Bladder segmentation was based on the SPECT images while CT slices were fused for anatomical confirmation. The Ordered Subset Estimation Maximization (OSEM) image reconstruction with collimator response, scatter and attenuation corrections was employed. Mean concentration (MBql/ml) measured in vivo by the software was compared and correlated to values obtained in vitro from the urine samples using the linear regression test (p<0.05 indicating significance).Results: Nine urine measurements were performed at 4 hours after injection, 9 after 24h, 3 after 48 and 5 after 72h. A total of 26 pairs of quantitative SPECT/CT studies and urinary samples were available for further analysis. A significant correlation (r=0.976, p < 0.0001) was obtained between the in vivo and in vitro measured bladder.Conclusion: LuP concentration can be reliably measured in vivo by SPECT/CT. The availability of noninvasive, non-laborious in vivo quantitation opens the potential for important clinical applications with the goal of optimization of radioligand therapy planning by personalized tailoring the treatment dose as well as for assessing response to treatment. Research Support: Not supported.