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Prostate Cancer Treatment and Research · Journal article
European Journal of Nuclear Medicine and Molecular Imaging · September 8, 2026
Early or partial results. Treat as a signal, not a conclusion.
This is a small, single-arm dosimetry study measuring organ and tumor absorbed doses from 161Tb-PSMA-617 in 15 mCRPC patients. The data show high tumor-absorbed doses (mean 5.95 ± 3.60 Gy/GBq) relative to kidneys and parotid glands (tumor-to-organ ratios 10.55 and 16.15 respectively), but the study is purely dosimetric and does not report clinical efficacy, safety events, or outcomes needed to guide clinical practice.
Single-arm registry dosimetry study. Patients with metastasized castration-resistant prostate cancer (mCRPC); registry enrollment NCT04833517; setting not specified. Intervention: [161Tb]Tb-PSMA-617 radioligand therapy; median 2 cycles, mean cumulative activity 12.3 ± 4.6 GBq. n = 15.
Mean absorbed dose to kidneys 0.70 ± 0.41 Gy/GBq; parotid glands 0.40 ± 0.20 Gy/GBq; submandibular glands 0.36 ± 0.14 Gy/GBq; liver 0.13 ± 0.08 Gy/GBq Mean overall tumor-absorbed dose 5.95 ± 3.60 Gy/GBq across 43 lesions with mean half-life 44.07 h ± 15.88 h Tumor-to-kidney ratio 10.55 ± 8.32 and tumor-to-parotid ratio 16.15 ± 11.85
No safety or toxicity events documented; only absorbed dose estimates provided Small sample size (n=15) and single-arm design preclude comparative efficacy or safety conclusions
Clinicians should interpret this as preliminary dosimetric characterization of a novel agent. The favorable tumor-to-organ ratios are encouraging but do not yet predict clinical benefit or safety outcomes; efficacy and toxicity data from controlled trials are needed before practice adoption.
First dosimetry characterization of 161Tb-PSMA-617 in a small, uncontrolled registry cohort without clinical outcome data, providing absorbed dose estimates but lacking efficacy, safety or comparative evidence.
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Clinicians should interpret this as preliminary dosimetric characterization of a novel agent. The favorable tumor-to-organ ratios are encouraging but do not yet predict clinical benefit or safety outcomes; efficacy and toxicity data from controlled trials are needed before practice adoption.
Graded across the dimensions that decide whether you should act, each from what the source actually supports. There is no single score, and where a dimension was not assessed it says so.
Abstract Purpose Terbium-161 ( 161 Tb) has emerged as a promising radionuclide for radioligand therapy (RLT) due to its emission of Auger and conversion electrons, which may support therapeutic efficacy through increased local energy deposition. Despite growing research efforts aimed at the clinical potential of 161 Tb, dosimetric data, particularly for tumor lesions, remain scarce. To address this gap, we assessed tumor and organ dosimetry in mCRPC patients treated with [ 161 Tb]Tb-PSMA-617. Methods The study involved n = 15 patients with metastasized castration-resistant prostate cancer (mCRPC) participating in a registry (NCT04833517) and receiving [ 161 Tb]Tb-PSMA-617. All patients received a median of 2 (range: 1–3) cycles with mean administered activity of 6.0 ± 1.3 GBq and mean cumulative activity of 12.3 ± 4.6 GBq [ 161 Tb]Tb-PSMA-617. Hybrid dosimetry of organs at risk, including the salivary glands, the kidneys, the liver, and tumor lesions was performed analyzing whole-body planar and SPECT/CT images. Absorbed doses were estimated using OLINDA/EXM for 161 Tb. Tumor-to-organ ratios (TR) of mean tumor-absorbed doses over relevant organs at risk were calculated. Results Mean absorbed dose to kidneys, parotid glands, submandibular glands and liver was 0.70 ± 0.41 Gy/GBq, 0.40 ± 0.20 Gy/GBq, 0.36 ± 0.14 Gy/GBq and 0.13 ± 0.08 Gy/GBq, respectively. Tumor kinetics in 43 lesions demonstrated stable activity over time (mean half-life of all lesions: 44.07 h ± 15.88 h) delivering a mean overall absorbed tumor dose of 5.95 ± 3.60 Gy/GBq, the resulting TR over kidney and parotid gland were 10.55 ± 8.32 and 16.15 ± 11.85, respectively. Conclusion [ 161 Tb]Tb-PSMA-617 delivers high tumor-absorbed doses with tolerable doses to relevant organs at risk, translating into favorable tumor-to-normal-organ ratios. Dosimetry results confirm 161 Tb as a promising radionuclide for PSMA-targeted radioligand therapy in mCRPC.
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