Last reviewed by Dr. Dharmender Malik on 8 May 2026 · this article reflects the published evidence and current clinical practice at FMRI Gurugram.
Introduction
The clinical promise of any radioligand therapy depends on the boring, unglamorous, mostly-invisible work of getting the radioactive medicine to the patient on the right day, in the right specification, in the right activity. For Lu-177, this is, by 2026, a relatively settled supply chain. For Terbium-161, it is not. This article is about how we have built a stable Tb-161 supply chain at FMRI Gurugram, and why patients should care about it.
The honest reason patients should care: a Tb-161 cycle that arrives a week late is, for some patients, a meaningful clinical setback — particularly in disease states where small advantages compound over time. A cycle that arrives at the wrong activity is worse — it forces a re-plan and a delay. A cycle that arrives at the wrong specification cannot be administered at all. The supply chain is invisible when it works and visible when it does not.
The Tb-161 supply problem
Tb-161 production is harder than Lu-177 production for three reasons:
- Production is concentrated in fewer cyclotron facilities globally. Lu-177 is produced at multiple commercial-scale facilities worldwide. Tb-161 is currently produced at a smaller number of facilities, mostly research and clinical-trial-focused.
- Half-life is short. Tb-161 has a half-life of 6.9 days. Like all short-lived isotopes, the time from production to administration must be kept tight, otherwise the activity at infusion is lower than planned and the dosimetry calculations have to be redone.
- Coordination is complex. The cyclotron schedule, the radiopharmacy preparation window, the air or ground transport route, the customs clearance (for international supply), and the patient's clinical schedule all have to align. Any one misalignment can force a reschedule.
None of these is unsolvable. They simply require active management — which is the operational discipline we have built around the Tb-161 programme.
How FMRI manages it
The Tb-161 programme at FMRI is anchored on three operational components:
Cyclotron supply partnership
FMRI has worked with established cyclotron production partners that can deliver Tb-161 of the required specification (radionuclidic purity, specific activity, chemical purity) on a predictable schedule. The supply contract is structured to align with our patient scheduling rather than to require us to align with the cyclotron's open production windows.
Dosimetry team
For every Tb-161 cycle, dosimetry calculations are performed by the FMRI medical physics and nuclear medicine team based on the patient's planning imaging. The calculation produces a target activity for the cycle, expressed at a defined time of administration. If the actual activity at delivery differs (because of decay during transit, for example), the calculation is adjusted before the infusion. This ensures the patient receives the planned absorbed dose to the target lesions, not just the labelled activity.
Scheduling discipline
Patient cycles are booked against the cyclotron production schedule, not the other way around. The cycle is confirmed only when the cyclotron production date is confirmed. This eliminates the bad outcome of a patient travelling to Gurugram on a date for which Tb-161 supply was uncertain.
"The patient does not see the cyclotron schedule. What the patient sees is a confirmed treatment date that does not move. That is the operational signature of a working supply chain."
What stable supply means
"Stable supply" is a slightly bland phrase. The concrete meaning, for a patient, is:
- Treatment dates do not move because of supply problems on our side.
- Cycle activities are delivered as planned, so the dosimetry plan is honoured.
- If a patient's clinical situation requires acceleration (cycle 3 needs to be brought forward by two weeks because of disease behaviour), the supply chain can absorb the change rather than block it.
- Subsequent cycles in the same patient are pre-planned, so the patient does not start each cycle from scratch in a scheduling sense.
- For international patients, travel and accommodation can be planned with confidence around fixed treatment dates.
The patient experience
From the patient's perspective, a Tb-161 cycle at FMRI looks like this:
- Week minus 6 — clinical evaluation, planning DOTATATE PET-CT or PSMA PET-CT (whichever is relevant for the indication), confirmation of eligibility and Helsinki-framework informed consent.
- Week minus 4 — dosimetry calculation completed; cyclotron production date confirmed; treatment date set; pre-cycle blood work scheduled.
- Week 0 — treatment day — admission to FMRI day-care; pre-infusion checks; Tb-161 infusion (typically 30 to 45 minutes); radiation-precaution monitoring; same-day or next-morning discharge.
- Weeks 1 to 8 between cycles — interval blood work, hormonal markers, follow-up consultation. Mid-course imaging after cycle 2 or 3.
- Subsequent cycles — scheduled in advance, supply pre-aligned, patient travel pre-planned.
The same flow operates whether the patient is from Delhi NCR, from elsewhere in India, or from international destinations. The fact that international patients can travel with confidence to fixed dates is a direct downstream effect of the supply chain working.
Looking for Tb-161 therapy with predictable scheduling?
Send your imaging and clinical summary. We respond with a treatment plan including specific cycle dates, dosimetry approach, and the Helsinki-framework consent material.
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For patients & referring clinicians
Frequently asked questions
Q01
Where can I get Tb-161 therapy in India?
Tb-161 therapy is available at a small number of specialised nuclear medicine centres in India including FMRI Gurugram, in the appropriate clinical-trial or named-patient framework.
Q02
How long is the wait for Tb-161 treatment?
Once eligibility is confirmed and planning imaging is in place, a Tb-161 cycle at FMRI is typically scheduled within 4 to 6 weeks. Subsequent cycles in the same patient are pre-planned.
Q03
Is Tb-161 always available?
Supply requires active management because Tb-161 is produced at fewer cyclotron facilities than Lu-177 and has a 6.9-day half-life. FMRI maintains a stable supply chain through cyclotron partnerships and disciplined scheduling, so confirmed treatment dates do not move.
Q04
What happens if there is a supply delay?
In the rare event of a delay, the team contacts the patient as early as possible, reschedules to the next production window (typically within 1 to 2 weeks), and adjusts dosimetry as needed. Patients are not asked to remain in Gurugram during a delay.
Citations & references
International Commission on Radiological Protection (ICRP). Guidance on radiopharmaceutical handling and patient release.
icrp.orgLehenberger S, Barkhausen C, Cohrs S, et al. The low-energy β− and electron emitter 161Tb as an alternative to 177Lu for targeted radionuclide therapy. Nucl Med Biol. 2011;38(6):917-924.
Müller C, Domnanich KA, Umbricht CA, van der Meulen NP. Scandium and terbium radionuclides for radiotheranostics: current state of development towards clinical application. Br J Radiol. 2018;91(1091):20180074.
About the Author
Dr. Ishita B. Sen
MBBS · MD (Nuclear Medicine) · DNB · Post-doctoral Fellowship, Memorial Sloan Kettering Cancer Center, New York
Director and Chief of Nuclear Medicine at Fortis Memorial Research Institute. Co-founder of Theranostic Physicians Private Limited (TPPL). Operational lead for the FMRI Tb-161 programme, working with the medical physics team to maintain stable supply and disciplined dosimetry.