# SPECT dosimetry workflow for radionuclide therapy

Source: https://nuclide.cc/technologies/spect-dosimetry-workflow/  
Nuclide record `spect-dosimetry-workflow` (Technology). Data CC BY-NC 4.0, attribute "Data from Nuclide (nuclide.cc)"; commercial use needs a licence.

## TL;DR

After a radioactive treatment injection, patients are scanned two or three times over about a week so doctors can calculate exactly how much radiation dose the tumour and organs like the kidneys actually received, and adjust future doses if needed.

## Summary

Clinical radionuclide-therapy dosimetry follows a standard sequence: sequential quantitative SPECT/CT (or hybrid planar-plus-SPECT/CT) imaging at multiple time points after administration, segmentation of source organs and tumours, fitting of time-activity curves to obtain the time-integrated activity in each region, and conversion to absorbed dose using either organ-level S-values (MIRD/OLINDA formalism) or voxel-level convolution/Monte Carlo methods. The EANM Dosimetry Committee's standard operational procedures, most recently the 2022 guideline for 177Lu-labelled somatostatin-receptor- and PSMA-targeting ligands, recommend using the same SPECT/CT system throughout a patient's dosimetry study, medium-energy collimators for 177Lu, iterative reconstruction with CT-based attenuation, scatter and (where available) collimator-response correction, and 60-120 projection angles at roughly 30-40 seconds per projection.

For kidney dosimetry, the guideline recommends three SPECT/CT acquisitions between 24 hours and 7 days after the first therapy cycle (with at least two days between the final two time points), reducing to a single acquisition at a matched time point for subsequent cycles, with the region of interest drawn to include the full renal cortex and medulla but exclude the pelvis. Tumour dosimetry follows a similar multi-time-point protocol, placing particular weight on a late imaging time point because tumour retention is typically slower than that of normal organs. A minimum of three time points is generally advised to characterise each exponential phase of the time-activity curve; two or three points at around 2, 4 and 24 hours are often sufficient for many source organs, but bone marrow and whole-body kinetics may need additional early sampling. Related standard operational procedures exist for 131I-mIBG neuroendocrine tumour therapy and for 90Y radioembolisation (99mTc-MAA pre-therapy and 90Y peri-therapy dosimetry).

## Fields

- Kind: Technology
- Last checked: 2026-09-22
- Also known as: post-therapy dosimetry; EANM dosimetry SOP
- Tags: dosimetry; clinical protocol; PRRT
- Principle: The patient is scanned with quantitative SPECT/CT at several defined time points after the therapy injection so that a time-activity curve can be fitted for each organ and tumour; integrating that curve gives the total number of decays in each region, which is then converted into an absorbed radiation dose using standardised organ- or voxel-level conversion factors.
- Since: First EANM dosimetry SOPs (radioiodine) 2008; MIRD Pamphlet 26 on quantitative 177Lu SPECT dosimetry 2016; PRRT/PSMA-specific guideline 2022

## Sources

- EANM dosimetry committee recommendations for dosimetry of 177Lu-labelled SSTR- and PSMA-targeting ligands (Eur J Nucl Med Mol Imaging 2022): https://link.springer.com/article/10.1007/s00259-022-05727-7
- PMC full text of the EANM 177Lu dosimetry recommendations: https://pmc.ncbi.nlm.nih.gov/articles/PMC9015994/
- EANM guidance document: dosimetry for first-in-human studies and phase 0/1 clinical trials (PMC 2024): https://pmc.ncbi.nlm.nih.gov/articles/PMC10957710/
- EANM: Radionuclide therapy management technologist guide: https://eanm.org/wp-content/uploads/2024/06/EANM22_TechGuide.pdf

## Connected records

- technologies: [Lutetium-177 radioligand therapy](https://nuclide.cc/technologies/lu177-radioligand-therapy/), [Monte Carlo dosimetry](https://nuclide.cc/technologies/monte-carlo-dosimetry/), [Peptide receptor radionuclide therapy (PRRT)](https://nuclide.cc/technologies/prrt/), [Quantitative SPECT](https://nuclide.cc/technologies/quantitative-spect/), [Radioligand dosimetry](https://nuclide.cc/technologies/radioligand-dosimetry/)
- isotopes: [Iodine-131](https://nuclide.cc/isotopes/i-131/), [Lutetium-177](https://nuclide.cc/isotopes/lu-177/), [Technetium-99m](https://nuclide.cc/isotopes/tc-99m/), [Yttrium-90](https://nuclide.cc/isotopes/y-90/)

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