RT Journal Article
SR Electronic
T1 Pretherapeutic Comparative Dosimetry of <sup>177</sup>Lu-rhPSMA-7.3 and <sup>177</sup>Lu-PSMA I&amp;T in Patients with Metastatic Castration-Resistant Prostate Cancer
JF Journal of Nuclear Medicine
JO J Nucl Med
FD Society of Nuclear Medicine
SP 833
OP 839
DO 10.2967/jnumed.121.262671
VO 63
IS 6
A1 Feuerecker, Benedikt
A1 Chantadisai, Maythinee
A1 Allmann, Anne
A1 Tauber, Robert
A1 Allmann, Jakob
A1 Steinhelfer, Lisa
A1 Rauscher, Isabel
A1 Wurzer, Alexander
A1 Wester, Hans-Jürgen
A1 Weber, Wolfgang A.
A1 d’Alessandria, Calogero
A1 Eiber, Matthias
YR 2022
UL http://jnm.snmjournals.org/content/63/6/833.abstract
AB Radiohybrid prostate-specific membrane antigen (rhPSMA) ligands allow for labeling with 18F and radiometals for endoradiotherapy. rhPSMA-7.3 has been designated as a lead compound with promising preclinical data for 177Lu-rhPSMA-7.3, which has shown higher tumor uptake than 177Lu-PSMA I&amp;T. In this retrospective analysis, we compared pretherapeutic clinical dosimetry data of both PSMA ligands. Methods: Six patients with metastatic castration-resistant prostate cancer underwent both 177Lu-rhPSMA-7.3 and 177Lu-PSMA I&amp;T pretherapeutic dosimetry. Whole-body scintigraphy was performed at 1 h, 4 h, 24 h, 48 h, and 7 d after injection. Regions of interest covering the whole body, organs, bone marrow, and tumor lesions were drawn for each patient. Absorbed doses for individual patients and pretherapeutic applications were calculated using OLINDA/EXM. To facilitate the comparison of both ligands, we introduced the therapeutic index (TI), defined as the ratio of mean pretherapeutic doses to tumor lesions over relevant organs at risk. Results: Mean whole-body pretherapeutic effective doses for 177Lu-rhPSMA-7.3 and 177Lu-PSMA I&amp;T were 0.12 ± 0.07 and 0.05 ± 0.03 Sv/GBq, respectively. Mean absorbed organ doses for 177Lu-rhPSMA-7.3 and 177Lu-PSMA I&amp;T were, for example, 1.65 ± 0.28 and 0.73 ± 0.18 Gy/GBq for the kidneys, 0.19 ± 0.09 and 0.07 ± 0.03 Gy/GBq for the liver, 2.35 ± 0.78 and 0.80 ± 0.41 Gy/GBq for the parotid gland, and 0.67 ± 0.62 and 0.30 ± 0.27 Gy/GBq for the bone marrow, respectively. Tumor lesions received mean absorbed doses of 177Lu-rhPSMA-7.3 and 177Lu-PSMA I&amp;T of 6.44 ± 6.44 and 2.64 ± 2.24 Gy/GBq, respectively. The mean TIs for the kidneys were 3.7 ± 2.2 and 3.6 ± 2.2 for 177Lu-rhPSMA-7.3 and 177Lu-PSMA I&amp;T, respectively, and those for the bone marrow were 15.2 ± 10.2 and 15.1 ± 10.2 for 177Lu-rhPSMA-7.3 and 177Lu-PSMA I&amp;T, respectively. Conclusion: Pretherapeutic clinical dosimetry confirmed preclinical results of mean absorbed doses for tumors that were 2–3 times higher for 177Lu-rhPSMA-7.3 than for 177Lu-PSMA I&amp;T. Absorbed doses to normal organs also tended to be higher for 177Lu-rhPSMA-7.3, resulting overall in similar average TIs for both radiopharmaceuticals with considerable interpatient variability. 177Lu-rhPSMA-7.3 has promise for a therapeutic efficacy similar to that of 177Lu-PSMA I&amp;T at smaller amounts of injected activity, simplifying radiation safety measurements (especially for large patient numbers or dose escalation regimens).