Radiation Dosimetry of 99mTc-PSMA I&S: A Single-Center Prospective Study

• Published in: The Journal of nuclear medicine (1978) Vol. 62; no. 8; p. 1075
• Main Authors: Urbán, Szabolcs, Meyer, Catherine, Dahlbom, Magnus, Farkas, István, Sipka, Gábor, Besenyi, Zsuzsanna, Czernin, Johannes, Calais, Jeremie, Pávics, László
• Format: Journal Article
• Language: English
• Published: New York Society of Nuclear Medicine 01.08.2021
• Subjects: Algorithms; Antigens; Biodistribution; Bladder; Computed tomography; Curve fitting; Dosimeters; Dosimetry; Image acquisition; Injection; Intestine; Medical imaging; Metastases; Muscles; Organs; Patients; Prostate; Prostate cancer; Radar; Radiation; Radiation dosage; Single photon emission computed tomography; Tumors; Websites
• ISSN: 0161-5505; 1535-5667; 1535-5667
• DOI: 10.2967/jnumed.120.253476

99mTc-PSMA I&S is a prostate-specific membrane antigen (PSMA) tracer that can be used for planar and SPECT/CT γ-imaging and radioguided surgery. The primary aim of this study was to estimate the dosimetry of 99mTc-PSMA I&S using a hybrid method (sequential γ-planar imaging and 1 single SPECT/CT) in healthy volunteers. The secondary aim was to depict the tracer biodistribution and tumor-to-background ratios (TBRs) in patients with prostate cancer (PCa). Methods: Dosimetry of 99mTc-PSMA I&S was investigated in 4 healthy volunteers. Whole-body planar imaging was acquired at 1, 2, 3, 6, and 24 h and SPECT/CT at 6 h after tracer injection. Contours of organs were drawn on all acquisitions to determine organ activity at each time point. Absorbed dose was estimated using 2 methods: independent curve-fitting manual method (Levenberg-Marquardt–based algorithm using dose factors from RAdiation Dose Assessment Resource [RADAR] website) and OLINDA/EXM software (version 2.0; HERMES Medical Solutions). Biodistribution of 99mTc-PSMA I&S was assessed in 10 patients with PCa on SPECT/CT images at 6 h. Tumor uptake (SUVmax), and TBR (tumor SUVmax/background organ SUVmean) using muscle (T/M), bladder (T/B), and intestine (T/I) as background organs were determined. Results: The mean injected activity of 99mTc-PSMA I&S was 717 MBq (range: 562–828 MBq). No adverse events related to the injection of 99mTc-PSMA I&S were reported. The average radiation effective dose was 0.0055 mSv/MBq with the RADAR manual method and 0.0052 mSv/MBq with OLINDA/EXM. Total body effective dose ranged between 3.33–4.42 and 3.11–4.23 mSv, respectively. All PCa patients showed high tracer uptake in primary and metastatic lesions with T/M, T/B, and T/I ranging from 5.29–110, 0.11–7.02, and 0.96–16.30, respectively. Conclusion: Effective doses of 99mTc-PSMA I&S were comparable to those known for most of the 99mTc tracers and was lower than for the 68Ga-labeled and 18F-labeled agents. 99mTc-PSMA I&S SPECT/CT showed high TBR in PCa patients. This study can provide required data for translation and approval of 99mTc-PSMA I&S by regulatory agencies.