Dosimetry in [177Lu]Lu-PSMA therapy is a valuable tool to assess treatment efficacy and toxicity. This study aims to develop a clinically implementable protocol to determine the absorbed dose in organs and tumor lesions after [177Lu]Lu-PSMA-617 therapy, by reducing the imaging time points and utilizing population-based kinetics with a single scan, with evaluation of its influence on the uncertainty in absorbed dose.
Ten patients with metastatic hormone-sensitive prostate cancer received two cycles of [177Lu]Lu-PSMA-617. Post-treatment imaging was performed at 1 h, 24 h, 48 h, 72 h and 168 h, consisting of three-bed positions SPECT/CT and a whole-body planar scan. Five-time point SPECT dosimetry was performed for lesions and organs with physiological uptake (kidneys, liver and salivary glands) and used as the reference standard. Absorbed dose values for various simplified protocols were compared to the reference standard.
Accurate lesion dosimetry is possible using one-time point SPECT imaging at 168 h, with an increase in uncertainty (20% vs. 14% for the reference standard). By including a second time point, uncertainty was comparable to the reference standard (13%). Organ dosimetry can be performed using a single SPECT at 24 h or 48 h. Dosimetry based on planar scans did not provide accurate dose estimations.
Accurate lesion dosimetry in [177Lu]Lu-PSMA therapy can be performed using a one- or two-time point protocol, making dosimetry assessments more suitable for routine clinical implementation, although dosimetry based om multiple time points is more accurate. Clinical trial registration This study was approved by the Medical Review Ethics Committee Region Arnhem-Nijmegen on January 23, 2018 and was registered on clinicaltrials.gov (NCT03828838).
EJNMMI research. 2023 Jan 24*** epublish ***
Steffie M B Peters, Maaike C T Mink, Bastiaan M Privé, Maarten de Bakker, Frank de Lange, Constantijn H J Muselaers, Niven Mehra, J Alfred Witjes, Martin Gotthardt, James Nagarajah, Mark W Konijnenberg
Department of Medical Imaging, Radboud University Medical Center, P.O. Box 9101, 6500 HB, Nijmegen, The Netherlands. ., Department of Medical Imaging, Radboud University Medical Center, P.O. Box 9101, 6500 HB, Nijmegen, The Netherlands., Department of Urology, Radboud University Medical Center, Nijmegen, The Netherlands., Department of Medical Oncology, Radboud University Medical Center, Nijmegen, The Netherlands.