Abstract
[68Ga]Ga-RM2 is a promising innovative positron emission tomography (PET) tracer for patients with primary or metastatic prostate carcinoma. This study aims to analyze the biodistribution and radiation dosimetry of [68Ga]Ga-RM2 in five prostate cancer patients. The percentages of injected activity in the source organs and blood samples were determined. Bone marrow residence time was calculated using an indirect blood-based method. OLINDA/EXM version 2.0 (Hermes Medical Solutions, Stockholm, Sweden) was used to determine residence times, organ absorbed and effective doses. Physiological uptake was seen in kidneys, urinary bladder, pancreas, stomach, spleen and liver. Blood clearance was fast and followed by rapid clearance of activity from kidneys resulting in high activity concentrations in the urinary bladder. The urinary bladder wall was the most irradiated organ with highest mean organ absorbed dose (0.470 mSv/MBq) followed by pancreas (0.124 mSv/MBq), stomach wall (0.063 mSv/MBq), kidneys (0.049 mSv/MBq) and red marrow (0.010 mSv/MBq). The effective dose was found to be 0.038 mSv/MBq. Organ absorbed doses were found to be comparable to other gallium-68 labelled GRPR antagonists and lower than [68Ga]Ga-PSMA with the exception of the urinary bladder, pancreas and stomach wall. Remarkable interindividual differences were observed for the organ absorbed doses. Therefore, [68Ga]Ga-RM2 is a safe diagnostic agent with a significantly lower kidney dose but higher pancreas and urinary bladder doses as compared to [68Ga]Ga-PSMA.
Highlights
Prostate carcinoma (PCa) is the second most common cancer in men worldwide and the most common cancer in European males
Five male patients (Table 1) with mean age of 71.4 years and biochemical recurrence of prostate cancer after radical prostatectomy were included in this retrospective analysis
In four patients with PSA elevation (PSA range 1.8–27.5 ng/mL) a [68 Ga]Ga-prostate-specific membrane antigen (PSMA)-positron emission tomography (PET)/CT showed no signs of local recurrence or metastases, the [68 Ga]Ga-RM2-PET/CT was performed
Summary
Prostate carcinoma (PCa) is the second most common cancer in men worldwide and the most common cancer in European males. It has an incidence rate of 31.1 per 100,000 and is the second common cause of cancer death in males [1]. The five-year survival after radical prostatectomy is usually 100% for localized disease and 28% with metastatic disease [3]. Morphological imaging modalities have limited sensitivity and specificity to detect local recurrence and metastatic disease [5]. In spite of this limitation, there is Radiation 2021, 1, 33–44; doi:10.3390/radiation1010004 www.mdpi.com/journal/radiation
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