TY - JOUR T1 - Radiation Dosimetry for <sup>177</sup>Lu-PSMA I&amp;T in Metastatic Castration-Resistant Prostate Cancer: Absorbed Dose in Normal Organs and Tumor Lesions JF - Journal of Nuclear Medicine JO - J Nucl Med SP - 445 LP - 450 DO - 10.2967/jnumed.116.178483 VL - 58 IS - 3 AU - Shozo Okamoto AU - Anne Thieme AU - Jakob Allmann AU - Calogero D’Alessandria AU - Tobias Maurer AU - Margitta Retz AU - Robert Tauber AU - Matthias M. Heck AU - Hans-Juergen Wester AU - Nagara Tamaki AU - Wolfgang P. Fendler AU - Ken Herrmann AU - Christian H. Pfob AU - Klemens Scheidhauer AU - Markus Schwaiger AU - Sibylle Ziegler AU - Matthias Eiber Y1 - 2017/03/01 UR - http://jnm.snmjournals.org/content/58/3/445.abstract N2 - Prostate-specific membrane antigen (PSMA)–targeted radioligand therapy is increasingly used in metastatic castration-resistant prostate cancer. We aimed to estimate the absorbed doses for normal organs and tumor lesions using 177Lu-PSMA I&amp;T (I&amp;T is imaging and therapy) in patients undergoing up to 4 cycles of radioligand therapy. Results were compared with pretherapeutic Glu-NH-CO-NH-Lys-(Ahx)-[68Ga(HBEDCC)] (68Ga-PSMA-HBED-CC) PET. Methods: A total of 34 cycles in 18 patients were analyzed retrospectively. In 15 patients the first, in 9 the second, in 5 the third, and in 5 the fourth cycle was analyzed, respectively. Whole-body scintigraphy was performed at least between 30–120 min, 24 h, and 6–8 d after administration. Regions of interest covering the whole body, organs, and up to 4 tumor lesions were drawn. Organ and tumor masses were derived from pretherapeutic 68Ga-PSMA-HBED-CC PET/CT. Absorbed doses for individual cycles were calculated using OLINDA/EXM. SUVs from pretherapeutic PET were compared with absorbed doses and with change of SUV. Results: The mean whole-body effective dose for all cycles was 0.06 ± 0.03 Sv/GBq. The mean absorbed organ doses were 0.72 ± 0.21 Gy/GBq for the kidneys; 0.12 ± 0.06 Gy/GBq for the liver; and 0.55 ± 0.14 Gy/GBq for the parotid, 0.64 ± 0.40 Gy/GBq for the submandibular, and 3.8 ± 1.4 Gy/GBq for the lacrimal glands. Absorbed organ doses were relatively constant among the 4 different cycles. Tumor lesions received a mean absorbed dose per cycle of 3.2 ± 2.6 Gy/GBq (range, 0.22–12 Gy/GBq). Doses to tumor lesions gradually decreased, with 3.5 ± 2.9 Gy/GBq for the first, 3.3 ± 2.5 Gy/GBq for the second, 2.7 ± 2.3 Gy/GBq for the third, and 2.4 ± 2.2 Gy/GBq for the fourth cycle. SUVs of pretherapeutic PET moderately correlated with absorbed dose (r = 0.44, P &lt; 0.001 for SUVmax; r = 0.43, P &lt; 0.001 for SUVmean) and moderately correlated with the change of SUV (r = 0.478, P &lt; 0.001 for SUVmax, and r = 0.50, P &lt; 0.001 for SUVmean). Conclusion: Organ- and tumor-absorbed doses for 177Lu-PSMA I&amp;T are comparable to recent reports and complement these with information on an excellent correlation between the 4 therapy cycles. With the kidneys representing the critical organ, a cumulative activity of 40 GBq of 177Lu-PSMA I&amp;T appears to be safe and justifiable. The correlation between pretherapeutic SUV and absorbed tumor dose emphasizes the need for PSMA-ligand PET imaging for patient selection. ER -