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Purpose: Prostate-specific membrane antigen (PSMA) is a promising molecular target for imaging of prostate adenocarcinoma. 68Ga-P16-093, a small molecule PSMA ligand, previously showed equivalent diagnostic performance compared to 68Ga-PSMA-11 PET/CT in a pilot study of prostate cancer patients with biochemical recurrence (BCR). We performed a pilot study for further characterization of 68Ga-P16-093 including comparison to conventional imaging.Procedures: Patients were enrolled into two cohorts. The biodistribution cohort included 8 treated prostate cancer patients without recurrence, who underwent 6 whole body PET/CT scans with urine sampling for dosimetry using OLINDA/EXM. The dynamic cohort included 15 patients with BCR and 2 patients with primary prostate cancer. Two patients with renal cell carcinoma were also enrolled for exploratory use. A dynamic PET/CT was followed by 2 whole body scans for imaging protocol optimization based on bootstrapped replicates. 68Ga-P16-093 PET/CT was compared for diagnostic performance against available 18F-fluciclovine PET/CT, 99mTc-MDP scintigraphy, diagnostic CT, and MRI.Results: 68Ga-P16-093 deposited similar effective dose (0.024 mSv/MBq) and lower urinary bladder dose (0.064 mSv/MBq) compared to 68Ga-PSMA-11. The kidneys were the critical organ (0.290 mSv/MBq). While higher injected activities were preferable, lower injected activities at 74-111 MBq (2-3 mCi) yielded 80% retention in signal-to-noise ratio. The optimal injection-to-scan interval was 60 min, with acceptable delay up to 90 min. 68Ga-P16-093 PET/CT showed superior diagnostic performance over conventional imaging with overall patient-level lesion detection rate of 71%, leading to a change in management in 42% of the patients.Conclusions: Based on its favorable imaging characteristics and diagnostic performance in prostate cancer, 68Ga-P16-093 PET/CT merits further investigation in larger clinical studies. [ABSTRACT FROM AUTHOR]

Accurate determination of the electronic shift and mechanical shift is very important for pinhole SPECT imaging. SPECT reconstruction can yield high-resolution images, but the electronic shift and mechanical shift must be well known. A previously discussed method for the calibration of the shifts is extended to compensate for an angular-dependent radius of rotation (ROR) and to allow for the fitting of multiple point-source scans with different source positions or different RORs. The proposed method allows for the simultaneous determination of electronic and mechanical shifts. A second method is also presented that uses averaging of point source centroid data to find the shifts. It is shown theoretically that there is a linear relationship between the average centroid in the transverse direction and the electronic shift and mechanical shift in the transverse direction. The slope and intercept of the line depend on the ROR and distance (R) of the point source from the axis of rotation. Thus, the shifts can be determined if there are multiple intersecting lines, generated by changing ROR and R. This linear picture is useful for conceptual understanding; however, its usefulness is reduced when the ROR varies with gantry angle. The theoretical formulas for slope and intercept suggest that the shifts should be more sensitive to changes in the ROR than in R. The sensitivities to changes in ROR and R were tested experimentally using both fitting methods. Results showed that both methods are more sensitive when ROR is changed instead of R, but the angular-dependent method is more robust when there are experimental imperfections. Index Terms--Calibration, pinhole, single photon emission computed tomography, SPECT.

Background: [18F]Fluortriopride (FTP) was developed as a dopamine D3-selective radiotracer, thought to be important to neurobiological reward pathways and implicated in drug addiction, Parkinson’s disease, and schizophrenia. Preclinical radiation dosimetry studies found the gallbladder wall received the highest dose. A gallbladder dose reduction intervention was simulated using a novel reduction model for healthy adults following fatty-meal consumption. The goals of this study were to assess whole body FTP human dosimetry and determine the feasibility of reducing absorbed dose to the gallbladder wall.Results: Effective dose without a fatty meal was 0.022 ± 0.002 mSv/MBq (± standard deviation) with highest organ dose of 0.436 ± 0.178 mSv/MBq to the gallbladder wall (n = 10). Predicted gallbladder dose reduction with fatty meal consumed was 67.4% (n = 10). Meal consumption by four repeat volunteers decreased average gallbladder dose by 71.3% (n = 4) compared to the original ten volunteers.Conclusions: Observed effective doses were adequately low to continue studying FTP uptake in humans. Validated dosimetry simulations indicate up to a 71% reduction in gallbladder dose can be achieved by employing intrinsic physiology to contract the gallbladder via fatty meal ingestion. This methodology for predicting gallbladder absorbed dose reduction from fatty meal consumption can be applied to other radiopharmaceuticals and radiotherapies. [ABSTRACT FROM AUTHOR]