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Updated: Sep 30, 2025
A Whole Body Dosimetry Protocol for Peptide-Receptor Radionuclide Therapy PRRT: 2D Planar Image and Hybrid 2D+3D SPECT/CT Image Methods
Published on: April 24, 2020
Modelling SPECT auto-contouring acquisitions for 177Lu & 131I molecular radiotherapy using new developments in
Gunjan Kayal1, Maxime Chauvin2, Erick Mora-Ramirez3
1CRCT, UMR 1037, INSERM, Université Toulouse III Paul Sabatier, Toulouse, France; SCK CEN, Belgian Nuclear Research Centre, Boeretang 200, Mol 2400, Belgium.
Monte Carlo modeling of SPECT imaging now includes auto-contouring acquisitions for improved activity quantification. This new non-circular orbit (NCO) mode is crucial for accurate SPECT imaging, especially with high-penetration isotopes.
Area of Science:
- Medical Imaging
- Nuclear Medicine
- Computational Modeling
Background:
- Monte Carlo (MC) modeling enhances Single-Photon Emission Computed Tomography (SPECT) activity quantification in Molecular Radiotherapy.
- Current GATE (Geant4 Application for Tomographic Emission) SPECT modeling is limited to circular orbit (CO) acquisitions, failing to replicate auto-contouring modes.
- Auto-contouring acquisitions, where the detector head moves closer to the patient, are essential for improving image resolution.
Purpose of the Study:
- To develop and validate an auto-contouring step-and-shoot acquisition mode within the GATE MC simulation toolkit for SPECT imaging.
- To enable more accurate modeling of non-circular orbit (NCO) SPECT acquisitions.
Main Methods:
- Modeled experimental SPECT acquisitions of 177Lu and 131I using Siemens Symbia T2 and GE Discovery 670 gamma cameras.
- Extracted detector head parameters (radial positions, angles) from experimental projections to define NCO detector motion.
- Validated the gamma camera model against experimental projections and simulated CO and NCO SPECT projections for phantoms.
Main Results:
- Experimental and simulated SPECT images showed good agreement, with gamma index passing rates (GIPR) of 96.27% (177Lu) and 92.89% (131I).
- Comparison of simulated CO and NCO SPECT projections revealed significant differences, particularly for 131I (GIPR 75.58%), highlighting the impact of NCO modeling.
- The developed NCO mode accurately reproduced experimental data.
Conclusions:
- The study successfully developed and validated an auto-contouring (NCO) acquisition mode for GATE SPECT modeling.
- This NCO modeling is essential for accurate SPECT imaging, particularly for isotopes with high septal penetration like 131I.
- The findings underscore the necessity of incorporating auto-contouring capabilities into MC simulations for advanced SPECT applications.
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