Quantitative SPECT/CT reconstruction for ¹⁷⁷Lu and ¹⁷⁷Lu/⁹⁰Y targeted radionuclide therapies

Area of Science:

• Nuclear Medicine
• Medical Imaging
• Radiotherapy Physics

Background:

• Quantitative accuracy in Single Photon Emission Computed Tomography/Computed Tomography (SPECT/CT) is vital for effective targeted radionuclide therapy (TRT).
• Pre- and post-therapy SPECT/CT scans are essential for dosimetry and treatment planning in TRT.
• Standard reconstruction methods often lack sufficient corrections for physical effects, leading to inaccuracies.

Purpose of the Study:

• To evaluate the quantitative accuracy of SPECT/CT imaging for TRT using phantom and patient data.
• To compare a hybrid reconstruction strategy with limited correction methods.
• To assess the impact of reconstruction accuracy on dosimetry for diagnostic and therapeutic radionuclide administrations.

Main Methods:

• Phantom experiments were conducted using (99m)Tc (diagnostic) and (177)Lu, (90)Y/(177)Lu (post-therapy).
• A hybrid reconstruction strategy combining model-based and window-based corrections was applied.
• Image reconstruction was performed on both phantom and patient pre- and post-therapy studies.

Main Results:

• The hybrid method yielded highly accurate absolute activity reconstructions across all phantom experiments (-3.3% to 2.9% for (99m)Tc, -1.6% to 1.6% for (177)Lu).
• Limited correction methods resulted in larger, case-specific errors.
• Patient data analysis showed significant overestimation of activity (29-39% for (99m)Tc, 105-218% for (177)Lu) without proper corrections.

Conclusions:

• The hybrid reconstruction strategy provides quantitatively accurate SPECT/CT imaging suitable for TRT applications.
• Physics-based reconstruction significantly improves image resolution and quantitative accuracy compared to limited correction methods.
• Accurate SPECT/CT quantification is critical to avoid substantial errors in TRT dosimetry and treatment assessment.