# Dosimetry standardisation for radioligand therapy

Source: https://nuclide.cc/bottlenecks/b-dosimetry-standardisation/  
Nuclide record `b-dosimetry-standardisation` (Bottleneck). Data CC BY-NC 4.0, attribute "Data from Nuclide (nuclide.cc)"; commercial use needs a licence.

## TL;DR

Doctors give almost every patient the same fixed amount of radioactive drug, rather than measuring how much radiation each person's tumour and organs actually absorb and adjusting the dose. Personalising the dose might work better for some patients, but nobody has yet proven it clearly enough for it to become the standard of care.

## Summary

177Lu-PSMA-617 (Pluvicto) is approved and almost always given at a fixed activity of 7.4 GBq every six weeks; the joint 2023 EANM/SNMMI procedure guideline confirms that patient-specific dosimetry is not mandatory for in-label use. Yet academic dosimetry studies show wide inter-patient variation: EANM Dosimetry Committee analyses report that the number of PRRT cycles needed to reach a preset kidney absorbed-dose limit ranges from 2 to 10 across patients, and the total activity required to hit that limit varies by a factor of roughly 1.5 for somatostatin-receptor therapy and by a factor of 3 for PSMA therapy.

The unresolved question is whether measuring and personalising that dose actually improves outcomes enough to justify the extra imaging burden. In its January 2025 reply to an EMA concept paper on clinical evaluation of therapeutic radiopharmaceuticals, EANM stated plainly that 'divergent opinion persists... the lack of sufficiently robust evidence demonstrating that personalizing administered activities based on dosimetry provides tangible benefits' means EANM does not hold a definitive position recommending dosimetry-guided over fixed-activity dosing. Methods themselves are only partly harmonised: the EANM Dosimetry Committee's 2022 recommendations for 177Lu-SSTR/PSMA dosimetry, and MIRD Pamphlet No. 26 for quantitative 177Lu SPECT, describe standard operating procedures, but implementation still varies by centre in imaging timepoints, segmentation method and software.

Alpha emitters add a further layer of difficulty: EANM's same 2025 submission flags that actinium-225's limited imaging potential on current nuclear-medicine cameras means image-based dosimetry approaches developed for beta emitters do not simply transfer across, and new strategies or technology are still needed.

## Fields

- Kind: Bottleneck
- Last checked: 2026-09-22
- Tags: dosimetry; standardisation; guideline
- Stage: data-knowledge
- Severity: moderate
- Metrics: Number of PRRT cycles needed to reach a preset kidney dose limit, across patients: range 2–10 cycles; Variation in total activity needed to reach a preset absorbed-dose limit: ~1.5-fold (SSTR therapy), ~3-fold (PSMA therapy); 177Lu-PSMA-617 approved regimen: fixed activity per cycle: 7.4 GBq (200 mCi) every 6 weeks (±1 week), dosimetry not mandatory in-label
- Causes: No large randomised trial has yet shown that dosimetry-guided individualised dosing improves survival or reduces toxicity compared with fixed-activity dosing.; Dosimetry protocols (imaging timepoints, organ/tumour segmentation, software) are not fully harmonised across centres, so results are not always directly comparable.; Multiple SPECT/CT imaging sessions over days add patient burden and resource use that many centres cannot absorb for every patient.; Alpha emitters such as actinium-225 are difficult to image directly with current nuclear medicine cameras, so beta-emitter dosimetry methods do not transfer straightforwardly.

## Sources

- EANM Dosimetry Committee recommendations for 177Lu-labelled SSTR/PSMA ligands (2022): https://link.springer.com/article/10.1007/s00259-022-05727-7
- Joint EANM/SNMMI procedure guideline for 177Lu-PSMA-RLT (2023): https://pmc.ncbi.nlm.nih.gov/articles/PMC10317889/
- EANM reply to EMA consultation on clinical evaluation of therapeutic radiopharmaceuticals (Jan 2025): https://eanm.org/wp-content/uploads/2025/02/EANM-Reply-to-the-public-consultation-on-the-European-Medicines-Agency-Concept-paper-on-clinical-evaluation-of-therapeutic-radiopharmaceuticals-in-oncology.pdf

## Connected records

- ideas: [Dosimetry-personalised PRRT instead of four fixed cycles](https://nuclide.cc/ideas/idea-net-dosimetry-prrt/), [Total-body PET for personalised radioligand dosing](https://nuclide.cc/ideas/idea-total-body-pet-dosimetry/)
- bottlenecks: [Wrong doses](https://nuclide.cc/bottlenecks/b-dose-optimisation/)
- isotopes: [Actinium-225](https://nuclide.cc/isotopes/ac-225/), [Lutetium-177](https://nuclide.cc/isotopes/lu-177/)
- technologies: [In vivo dosimetry and patient-specific quality assurance](https://nuclide.cc/technologies/in-vivo-dosimetry/), [Peptide receptor radionuclide therapy (PRRT)](https://nuclide.cc/technologies/prrt/), [Quantitative imaging biomarkers (RECIST, PERCIST, SUV, ADC)](https://nuclide.cc/technologies/quantitative-imaging-biomarkers/), [Radioligand dosimetry](https://nuclide.cc/technologies/radioligand-dosimetry/)
- drugs: [Lutetium-177 dotatate](https://nuclide.cc/drugs/lutathera/), [Lutetium-177 vipivotide tetraxetan](https://nuclide.cc/drugs/pluvicto/)
- institutions: [European Association of Nuclear Medicine](https://nuclide.cc/institutions/eanm/), [European Medicines Agency](https://nuclide.cc/institutions/ema/), [Society of Nuclear Medicine and Molecular Imaging](https://nuclide.cc/institutions/snmmi/)

---
JSON: https://nuclide.cc/api/v1/entities/b-dosimetry-standardisation.json