The
chemokine receptor 4 (CXCR4), which is overexpressed in many solid and
hematologic malignancies, can be targeted for radiopeptide
therapy via the antagonist pentixather. The biokinetics and dosimetry of
177Lu-pentixather and
90Y-pentixather were analyzed in this study. Methods: This retrospective study was a standardized reevaluation of data collected for treatment planning. Nineteen patients with complete sets of planar whole-body scans over at least 4 d and a single SPECT/CT scan after administration of 200 MBq of
177Lu-pentixather were included. Kinetics were measured in the whole body, in tissues with activity retention, and in 10 individuals in the blood. Time-integrated activity coefficients and tissue-absorbed doses were derived. Results: Increased uptake of pentixather was observed in the kidneys, liver, spleen, and bone marrow, inducing respective median absorbed doses of 0.91 Gy (range, 0.38-3.47 Gy), 0.71 Gy (range, 0.39-1.17 Gy), 0.58 Gy (range, 0.34-2.26 Gy), and 0.47 Gy (range, 0.14-2.33 Gy) per GBq of
177Lu-pentixather and 3.75 Gy (range, 1.48-12.2 Gy), 1.61 Gy (range, 1.14-2.97 Gy), 1.66 Gy (range, 0.97-6.69 Gy), and 1.06 Gy (range, 0.27-4.45 Gy) per GBq of
90Y-pentixather. In most tissues, activity increased during the first day after the administration of
177Lu-pentixather and afterward decayed with mean effective half-lives of 41 ± 10 h (range, 24-64 h) in the kidneys and median half-lives of 109, 86, and 92 h in the liver, spleen, and bone marrow, respectively. Maximum uptake per kidney was 2.2% ± 1.0% (range, 0.6%-5.1%). In organs showing no specific uptake, absorbed doses exceeding 0.3 Gy/GBq of
90Y-pentixather were estimated for the urinary bladder and for tissues adjacent to accumulating organs such as the adrenal glands, bone surface, and gallbladder. Dose estimates for
tumors and extramedullary lesions ranged from 1.5 to 18.2 Gy/GBq of
90Y-pentixather. Conclusion: In patients with
hematologic neoplasms, absorbed doses calculated for bone marrow and extramedullary lesions are sufficient to be effective as an adjunct to high-dose
chemotherapies before
stem cell transplantation.