Assessing the feasibility of quantitative SPECT imaging for low ²¹²Pb activity concentrations using anthropomorphic...

Area of Science:

• Nuclear Medicine
• Radiopharmaceutical Therapy
• Medical Imaging

Background:

• Lead-212 (212Pb) is a promising alpha-emitter for targeted cancer therapy.
• Accurate imaging is crucial for dosimetry but challenging due to 212Pb's properties.

Purpose of the Study:

• To evaluate the quantitative accuracy of 212Pb SPECT imaging.
• To assess SPECT performance in patient-specific geometries and low activity concentrations.

Main Methods:

• An anthropomorphic phantom with 3D-printed organs (kidneys, liver, vertebrae) was used.
• 212Pb activity distribution was based on a patient's PSMA-1007 PET image.
• SPECT/CT imaging was performed, followed by Flash-3D reconstruction and comparison with gamma counter measurements.

Main Results:

• Quantification accuracy varied with reconstruction parameters; optimal results used 30-120 updates.
• Low activity concentrations (<0.05 kBq/ml) were not quantifiable (deviations >400%).
• Liver and kidney activity was underestimated by 10-50%, with <8% precision for higher activity images.

Conclusions:

• Larger volumes (liver, kidneys) with activity ≥210 Bq/ml may be quantifiable with ~30-40% accuracy.
• SPECT imaging can be valuable for dosimetry, especially for later time points in time-activity curves.
• Very low activity concentrations (<54 Bq/ml) remain unquantifiable.