— 01 · At a Glance
What is Tb-161 therapy?
★ In one paragraph
Terbium-161 is a radioactive isotope that behaves chemically and biologically just like the well-established lutetium-177 — the same DOTA-based ligands (PSMA-617 for prostate cancer, DOTATATE for neuroendocrine tumours), the same patient prep, the same dose schedule. The difference is in the radiation it emits: beta particles plus low-energy conversion and Auger electrons. Those extra electrons deliver dense short-range cytotoxic dose to micrometastases where Lu-177's beta range overshoots and under-treats.
Tb-161 is an emerging compassionate-use therapy — not yet FDA, EMA, or Indian regulator-approved as standard care, but with a growing prospective evidence base from PSI Switzerland, the University Hospital of Berne, Saarland (Germany), and AIIMS Delhi. We offer 161Tb-PSMA-617 and 161Tb-DOTATATE at our centre on an individualised compassionate use basis for eligible patients.
For most patients, the practical experience of Tb-161 therapy is indistinguishable from Lu-177 therapy — same outpatient infusion, same monitoring, same cycle schedule. What changes is the underlying radiobiology, and the theoretical (and in early trials documented) advantage in micrometastases-dominant disease.
— 02 · The Physics
Beta plus Auger plus conversion electrons.
Lu-177 is a pure beta-minus emitter — one type of radiation, one tissue range (~2 mm), one therapeutic effect. Tb-161 is a mixed emitter, and that mixed signature is what makes it interesting:
- Beta-minus particles — with average energy 154 keV (vs 134 keV for Lu-177) and maximum 593 keV (vs 498 keV for Lu-177). Practically identical to Lu-177 in tissue range and therapeutic effect on bulk disease.
- Conversion electrons — lower-energy electrons released when nuclear de-excitation transfers energy to an orbital electron. Tissue range on the order of micrometres — cell-scale.
- Auger electrons — very low energy electrons released when an inner-shell vacancy is filled. Sub-micrometre range, but extremely high local energy deposition. The most cytotoxic emission per micrometre travelled in clinical radiotherapy.
The net result: Tb-161 delivers the same bulk-disease dose as Lu-177 (via beta) plus an additional cell-scale dose (via Auger and conversion electrons) precisely at the locations where the targeting molecule has bound — the surface and interior of tumour cells. This additional dose is theoretically (and in published preclinical and early clinical work, demonstrably) advantageous against micrometastases and minimal residual disease where beta-only therapy under-treats.
161Tb
EMISSION COMPARISON
[Image: Side-by-side mechanism diagram — Lu-177 beta-only emission around a tumour cell vs Tb-161 mixed beta + Auger + conversion electron emission showing the additional short-range dose deposition pattern at the cell surface and within the cell]
— 03 · Side by Side
Lutetium-177 vs Terbium-161.
The two radionuclides are remarkably similar in everything except their final emission profile. Practically, Tb-161 is a near-perfect substitute for Lu-177 with one therapeutic addition.
Standard · established
Lutetium 177
The international standard radioligand isotope for PSMA therapy and PRRT. Regulator-approved (Pluvicto, Lutathera), reimbursed by major insurers, mature evidence base from VISION and NETTER-1 trials.
ParticleBeta only · ~2 mm range
Half-life6.7 days
Beta energy134 keV avg
Other emissionNone
Best forBulk disease, established standard
Next-gen · emerging
Terbium 161
Same DOTA chemistry, same ligands, same protocol — with added Auger and conversion electrons for extra short-range dose to micrometastases. Compassionate-use clinical practice.
ParticleBeta + Auger + conversion
Half-life6.9 days
Beta energy154 keV avg
Other emissionAuger + conversion electrons
Best forMicrometastases-dominant disease
— 04 · When Tb-161 Wins
Where the extra electrons matter.
For most patients, Lu-177 and Tb-161 will produce similar clinical outcomes — both effective, both manageable, both within the same protocol. The clinical scenarios where Tb-161 may offer a meaningful advantage:
- Micrometastases-dominant disease. Patients whose imaging shows many small lesions rather than bulky masses. Beta radiation's 2 mm range deposits most of its energy outside the lesion in small tumour foci; Auger and conversion electrons concentrate dose precisely where the molecule has bound.
- Bone-marrow disseminated disease. In mCRPC patients with extensive marrow infiltration but small individual lesions, the cell-scale dose from Auger electrons may improve local cytotoxicity while limiting collateral marrow damage from beta crossfire.
- Minimal residual disease after standard therapy. Patients with biochemical evidence of disease (rising PSA, rising chromogranin A) but limited visible disease — potentially the strongest theoretical use case for Tb-161 over Lu-177.
- Selected first-line or earlier-line use. In specific patient profiles where multidisciplinary review favours the additional electron dose from the outset.
★ Honest framing
Tb-161 is an emerging therapy, not a settled standard of care. Head-to-head randomised trials versus Lu-177 are ongoing, not yet published. We offer Tb-161 because the radiobiology rationale is sound, the early prospective evidence is promising, and our department has the technical capability and isotope supply chain.
We discuss the trade-offs openly with each patient: Lu-177 is mature and reimbursed; Tb-161 is emerging and self-funded. The choice is made with the referring oncologist and patient together.
— 05 · Indications
What Tb-161 currently treats.
Two clinical applications have mature ligand pairing and early prospective clinical evidence:
For metastatic castration-resistant prostate cancer with PSMA-PET positive disease. Particularly considered where disease is small-volume or micrometastases-dominant. First-in-human series from PSI Switzerland (Rosar et al.) demonstrated feasibility and acceptable safety with comparable response signal to Lu-PSMA in matched patients. Cross-references our Lu-PSMA page for the standard alternative.
161Tb-DOTATATE
SSTR-positive NETs
For SSTR-2-positive neuroendocrine tumours — gastroenteropancreatic NETs, lung NETs, paragangliomas. The Tb-161 equivalent of Lu-DOTATATE PRRT. Considered particularly for small-volume disseminated NET disease or as an alternative to Lu-DOTATATE in selected first-line patients. Cross-references our PRRT page for the standard pathway.
Additional Tb-161 ligand combinations are under preclinical and early clinical development worldwide — including FAP inhibitors, integrin-targeting peptides, and others. None are yet at routine clinical translation in India.
— 06 · Eligibility
Who is a candidate?
Tb-161 therapy at our centre is offered to patients meeting standard radioligand eligibility, with case-by-case multidisciplinary review:
- Histologically confirmed metastatic castration-resistant prostate cancer (for Tb-PSMA) or SSTR-positive neuroendocrine tumour (for Tb-DOTATATE).
- Target expression confirmed on diagnostic PET — PSMA-PET for prostate cancer (typically SUVmax > liver in the dominant lesions) or 68Ga-DOTATATE PET for NETs.
- Disease pattern review — the multidisciplinary team considers whether the patient's disease pattern (micrometastases vs bulky, marrow vs visceral) makes Tb-161 a reasonable alternative to Lu-177.
- Adequate organ function: creatinine clearance > 50 mL/min, haemoglobin > 9 g/dL, platelets > 100 × 10⁹/L, AST/ALT < 3× upper limit.
- Life expectancy > 6 months and ECOG performance status 0–2.
- Informed consent regarding the compassionate-use nature of Tb-161 therapy and the availability of regulator-approved Lu-177 as the standard alternative.
— 07 · Protocol
The treatment cycle.
Tb-161 protocol mirrors Lu-177 PSMA-617 or Lu-177 DOTATATE almost step-for-step:
01
Pre-treatment work-up
Target-specific diagnostic PET (PSMA-PET or 68Ga-DOTATATE PET). Baseline bloods, renal function, liver function. Disease-specific biomarkers (PSA for prostate, chromogranin A for NETs). Multidisciplinary tumour board review.
02
Pre-medication
For DOTATATE protocols: amino acid renal protection (lysine-arginine infusion) starting 30 minutes before therapy and continuing 4 hours. For PSMA protocols: salivary gland cooling (ice packs to parotids) during infusion to reduce xerostomia.
03
Therapy infusion · outpatient
Slow IV infusion of approximately 7.4 GBq Tb-161 ligand over 20–30 minutes with continuous monitoring. Antiemetic premedication. Total day-of-therapy time approximately 6 hours including pre-medication.
04
Interim review · cycle 3
Clinical assessment, biochemistry, and PSMA-PET or DOTATATE-PET imaging between cycles 3 and 4. Decision to continue, pause or escalate based on response, biomarker trends, and tolerability.
Cycle repeated 4 to 6 times at 6 to 8 week intervals, with response assessment between cycles 3 and 4 and again after the final cycle. Total course duration typically 7 to 11 months.
— 08 · Evidence
What the data shows.
Tb-161 is an emerging isotope — the clinical literature is small but growing, with consistent signal supporting feasibility, safety and equivalent-or-better efficacy compared to Lu-177 in matched populations.
2019
Preclinical PSMA superiority published (Müller, PSI)
2021
First-in-human DOTATATE in Switzerland
2023
First-in-human PSMA-617 SPECT series (Rosar)
The PSI Switzerland origin
The Paul Scherrer Institute (PSI) in Villigen, Switzerland led by Cristina Müller1 developed and optimised the production chemistry, dosimetry calculations and preclinical evidence base for Tb-161. The 2019 Journal of Nuclear Medicine publication established the theoretical and practical case for replacing Lu-177 with Tb-161 in PSMA-targeted radioligand therapy.
First-in-human DOTATATE
The University Hospital of Berne reported the first clinical use3 of 161Tb-DOTATATE in a small patient series with progressive neuroendocrine tumours. The series confirmed feasibility, acceptable safety, and treatment response in patients with prior Lu-DOTATATE exposure — supporting Tb-161 both as alternative first-line and as salvage option.
First-in-human PSMA-617
Rosar et al.2 at Saarland University Hospital reported the first SPECT-imaging-confirmed clinical application of 161Tb-PSMA-617 in patients with metastatic prostate cancer. The series documented the expected biodistribution, comparable tumour uptake to Lu-PSMA-617 dosimetry historical controls, and acceptable tolerability profile. Larger prospective trials are now in early phase enrollment internationally.
— 09 · Tolerability
Side effects.
Tb-161 side effects closely mirror Lu-177 in the same clinical context — because the ligand (PSMA-617 or DOTATATE) is what determines biodistribution, and the additional Auger/conversion electrons act at the same molecular target sites, with limited additional off-target effect.
Common (>15% of patients)
- Mild fatigue — typically 1 to 2 weeks after each cycle.
- Mild nausea — controlled by pre-medication; less frequent than chemotherapy.
- Transient cytopenia — reductions in haemoglobin, platelets, lymphocytes; nadir at 4 to 6 weeks, recovery by 10 to 12 weeks.
- Xerostomia (PSMA context) — salivary gland dose; mitigated by ice-pack cooling during infusion.
Uncommon (1–15%)
- Renal effects — mild creatinine rise; mitigated by amino acid renal protection in DOTATATE protocols.
- Hepatic dysfunction — in patients with extensive hepatic disease.
- Persistent cytopenia requiring growth factor support — in heavily pre-treated patients.
Rare but serious
- Severe and prolonged cytopenia — particularly in patients with prior heavy chemotherapy or marrow disease.
- Late renal toxicity — rare with appropriate amino acid protection.
- Secondary haematological malignancy — very rare; risk grows with cumulative radiation exposure.
— 10 · Pricing
Cost in India.
Indicative cycle pricing. Figures cover the radiopharmaceutical, infusion suite, pre-medication and standard monitoring. Target-specific PET imaging and inpatient stay billed separately.
| Variant |
Per cycle |
4-cycle course |
161Tb-PSMA-617 (Indian) |
~ ₹ 5,17,000
~ USD 5,744 |
~ ₹ 20.7 L
~ USD 23,000 |
161Tb-PSMA-617 (international) |
~ ₹ 7,50,000
~ USD 8,333 |
~ ₹ 30 L
~ USD 33,333 |
161Tb-DOTATATE (Indian) |
~ ₹ 5,17,000
~ USD 5,744 |
~ ₹ 20.7 L
~ USD 23,000 |
161Tb-DOTATATE (international) |
~ ₹ 7,50,000
~ USD 8,333 |
~ ₹ 30 L
~ USD 33,333 |
★ Please read
Figures are indicative ranges, not quotes, presented at 1 USD = ₹ 90. They cover therapy fees only. A formal written quote is issued after pre-treatment evaluation.
Because Tb-161 is investigational compassionate use, insurance coverage is currently limited — most patients self-fund. Where the patient qualifies for Lu-177 PSMA or PRRT and chooses Tb-161 instead, some insurers will reimburse the Lu-177 equivalent value. WhatsApp us for a pre-authorisation pack.
— 11 · Availability
Next available Tb-161 slots.
Tb-161 therapy at our centre is scheduled monthly, governed by terbium-161 supply availability from European producers. Reservations require 7 days advance notice for radiopharmaceutical procurement.
Tb-161 calendar — next slots.
Frequently asked questions.
Terbium-161 (Tb-161) treatment is a next-generation radioligand therapy using the radionuclide terbium-161 chemically attached to a targeting molecule — most commonly PSMA-617 for metastatic prostate cancer or DOTATATE for neuroendocrine tumours.
Tb-161 emits the same therapeutic beta-minus radiation as the established Lu-177 isotope, but additionally produces low-energy conversion and Auger electrons. These extra electrons deliver dense, short-range cytotoxic radiation to micrometastases — small disease foci that beta radiation alone tends to overshoot. The protocol, infusion, and patient experience are practically identical to Lu-PSMA or Lu-DOTATATE therapy.
Terbium-161 decays primarily by beta-minus emission to stable dysprosium-161. The average beta energy is approximately 154 keV with a maximum of 593 keV — closely matching the energy profile of Lu-177.
Crucially, in addition to beta decay, Tb-161 emits internal conversion and Auger electrons (low-energy electrons with very short tissue range, on the order of micrometres). The combined emission profile delivers both medium-range beta dose to bulk disease and dense short-range dose to micrometastases, an emission signature unique to Tb-161 in current clinical radionuclide therapy.
Terbium-161 has a physical half-life of approximately 6.9 days. This is very close to the half-life of lutetium-177 (6.7 days), which is why the same dosing schedule, infusion logistics, and inter-cycle intervals used for Lu-PSMA or Lu-DOTATATE PRRT apply directly to the Tb-161 equivalents.
Among the terbium isotopes, four are of clinical theranostic interest — terbium-149 (alpha emitter), terbium-152 (positron emitter for PET imaging), terbium-155 (gamma emitter for SPECT imaging), and terbium-161 (beta + Auger + conversion electron emitter for therapy).
Terbium-161 is the most clinically advanced of the four, with first-in-human PSMA and DOTATATE trials reported from Switzerland (PSI / University of Berne) and case-series experience in Germany and India. The theoretical advantage of Tb-161 over Lu-177 is the additional Auger/conversion electron dose delivered to small tumour foci.
Chemically, Tb-161 and Lu-177 behave almost identically — both are trivalent lanthanide ions that conjugate to DOTA-based ligands using the same chemistry. Biologically, the same targeting molecules (PSMA-617, DOTATATE) work for both, with the same pharmacokinetics and biodistribution.
The difference is in the emission profile: Lu-177 emits only beta particles, whereas Tb-161 emits beta particles plus low-energy conversion and Auger electrons. The additional electron emission delivers extra short-range dose, theoretically advantageous against micrometastases and minimal residual disease where pure beta tends to under-treat.
Terbium-161 therapy is not yet approved by the FDA, EMA, or the Indian regulator as a standard cancer therapy. It remains an emerging compassionate-use treatment offered at specialist theranostic centres internationally, with growing clinical evidence base.
At our centre we offer 161Tb-PSMA-617 and 161Tb-DOTATATE on an individualised compassionate use basis for patients meeting eligibility criteria, after multidisciplinary tumour-board review.
Candidates include patients with metastatic castration-resistant prostate cancer (for 161Tb-PSMA-617) or SSTR-2-positive neuroendocrine tumours (for 161Tb-DOTATATE) — particularly those with a micrometastatic or minimal-residual-disease pattern where Tb-161's additional short-range electron dose may provide therapeutic advantage over conventional Lu-177.
Eligibility requires confirmed PSMA or SSTR-2 expression on the corresponding diagnostic PET, adequate organ function, and multidisciplinary review.
Most Tb-161 protocols follow the same cycle structure as the Lu-177 equivalent — 4 to 6 cycles spaced 6 to 8 weeks apart. Each cycle is an outpatient infusion of approximately 7.4 GBq (or weight-based equivalent), with interim response review by PSMA-PET or DOTATATE-PET around cycle 3.
At Theranostic Physicians, Tb-161 therapy is priced individually per cycle. Indicative range: approximately ₹ 5,17,000 per cycle for Indian patients, and approximately ₹ 7,50,000 per cycle for international patients (around USD 8,333 at current exchange).
A typical 4-cycle course totals approximately ₹ 20 lakh for Indian patients and ₹ 30 lakh for international patients. A formal written quote is issued after pre-treatment evaluation.
Side effects of Tb-161 therapy closely mirror those of Lu-177 in the same clinical context. Common: mild fatigue, mild nausea, transient reductions in blood counts (haemoglobin, platelets, lymphocytes).
Xerostomia (dry mouth) occurs when paired with PSMA targeting (similar incidence to Lu-PSMA, since salivary gland PSMA expression is the dominant factor — not the radionuclide). Renal effects mild and protected by amino acid infusion in DOTATATE protocols.
IS
[Image: Dr. Sen portrait]
Written & Medically Reviewed By
Dr. Ishita B. Sen
MBBS · DRM · DNB (Nuclear Medicine) · 30+ years in nuclear oncology
Director and Head, Department of Nuclear Medicine and Molecular Imaging, Fortis Memorial Research Institute. Visiting fellowships at Memorial Sloan Kettering Cancer Center, New York and University of Marburg, Germany. Past President, Association of Nuclear Medicine Physicians of India. Active interest in next-generation radioligand isotopes including terbium-161 and lead-212.
FellowshipsMSK New York · Marburg
Past PresidentANMPI
SpecialityNext-gen theranostic isotopes
Full profile
References & citations
- Müller C, Umbricht CA, Gracheva N, et al. Terbium-161 for PSMA-targeted radionuclide therapy of prostate cancer. European Journal of Nuclear Medicine and Molecular Imaging, 2019;46(9):1919–1930. DOI: 10.1007/s00259-019-04345-0 — PSI Switzerland foundational paper.
- Rosar F, Maus S, Schaefer-Schuler A, et al. 161Tb-PSMA Radioligand Therapy: First-in-Humans SPECT/CT Imaging. Journal of Nuclear Medicine, 2023;64(8):1322–1326. JNM — Saarland first clinical PSMA series.
- Baum RP, Singh A, Kulkarni HR, et al. First-in-Human Application of Terbium-161: A Feasibility Study Using 161Tb-DOTATOC. Journal of Nuclear Medicine, 2021;62(10):1391–1397. — Bad Berka first DOTATATE-equivalent in human.
- Borgna F, Haller S, Mönch M, et al. Replacing Lu-177 with Tb-161 in DOTA-TATE and PSMA-617 radiopharmaceuticals: a feasibility study. EJNMMI Physics, 2023;10:42. EJNMMI Physics
- Paul Scherrer Institute (PSI), Switzerland. Terbium-161: new radionuclide therapy hits the clinic. PSI Scientific Highlights, 2021. PSI — clinical translation press piece.
- Sartor O, Sharma D. Targeted radioactive therapy for prostate cancer (Comment). The Lancet, 2021;397(10286):1623–1624. — broader context on emerging PSMA radioligand isotopes.