Biodistribution and radiation dosimetry of [18F]-JK-PSMA-7 as a novel prostate-specific membrane antigen-specific ligand for PET/CT imaging of prostate cancer

Aim We investigated the whole-body distribution and the radiation dosimetry of [18F]-JK-PSMA-7, a novel 18F-labeled PSMA-ligand for PET/CT imaging of prostate cancer. Methods Ten patients with prostate cancer and biochemical recurrence or radiologic evidence of metastatic diseases were examined with 329–384 MBq (mean 359 ± 17 MBq) [18F]-JK-PSMA-7. Eight sequential positron emission tomography (PET) scans were acquired from 20 min to 3 h after injection with IRB approval. The kidneys, liver, lungs, spleen, and salivary glands were segmented into volumes of interest using the QDOSE dosimetry software suite (ABX-CRO, Germany). Absorbed and effective dose were calculated using the ICRP-endorsed IDAC 1.0 package. The absorbed dose of the salivary glands was determined using the spherical model of OLINDA 1.1. PSMA-positive lesions were evaluated separately. Quantitative assessment of the uptake in suspicious lesions was performed by analysis of maximum (max) and peak SUV values. The gluteus maximus muscle (SUVmean) served as a reference region for the calculation of tumor-to-background ratios (TBR’s). Results Physiologic radiotracer accumulation was observed in the salivary and lacrimal glands, liver, spleen, and intestines, in a pattern resembling the distribution known from other PSMA-tracers with excretion via urinary and biliary pathways. The effective dose from [18F]-JK-PSMA-7 for the whole body was calculated to be 1.09E−02 mGy/MBq. The highest radiation dose was observed in the kidneys (1.76E−01 mGy/MBq), followed by liver (7.61E−02 mGy/MBq), salivary glands (4.68E−02 mGy/MBq), spleen (1.89E−02 mGy/MBq), and lungs (1.10E-2 mGy/MBq). No adverse effects of tracer injection were observed. Six out of ten patients were scored as PSMA-positive. A total of 18 suspicious lesions were analyzed, which included six bone lesions, nine lymph nodes, and three local lesions within the prostate fossa. The values for the SUVmax and SUVpeak in the PSMA-positive lesions increased until 60 min p.i. and remained at this intensity in the PET/CT scans until 140 min. In the period between 170 and 200 min after injection, a further significant increase in SUVmax and SUVpeak within the PSMA-positive lesions was observed. Conclusions The highest TBR of [18F]-JK-PSMA-7 was found 3 h after injection. From the kinetically collected data, it can be concluded that this trend may also continue in the further course. The start of the PET/CT acquisition should be chosen as late as possible. The high uptake in suspicious lesions in terms of absolute SUVmax and relative TBR values indicates potentially high sensitivity of the tracer for detection of prostate cancer manifestations.