Development and evaluation of a model-based downscatter compensation method for quantitative I-131 SPECT

Area of Science:

• Nuclear medicine
• Medical physics
• Radiopharmaceutical therapy

Background:

• Iodine-131 (131I) is crucial for targeted radionuclide therapy (TRT), requiring accurate activity quantification for treatment planning and verification.
• Quantitative single-photon emission computed tomography (QSPECT) enables in vivo activity estimation but is challenged by downscatter from higher-energy photons.
• Downscatter degrades image contrast and quantitative accuracy in 131I imaging.

Purpose of the Study:

• To develop and evaluate a model-based downscatter compensation method for 131I imaging.
• To specifically address the compensation of high-energy photons detected in the 364 keV photopeak energy window.
• To improve the accuracy of quantitative 131I imaging for TRT applications.

Main Methods:

• Validated a Monte Carlo simulation (MCS) code for 131I imaging.
• Assessed the accuracy of a downscatter model by comparing its estimates with MCS results.
• Integrated the downscatter model with iterative reconstruction for attenuation (A), scatter (S), and collimator-detector response (D) compensation.
• Evaluated the comprehensive compensation method using the 3D NCAT phantom and patient data.

Main Results:

• The proposed downscatter compensation method significantly improved quantitative accuracy.
• The method's accuracy was comparable to reconstructions using projections without downscatter contamination.
• Substantial improvements were observed compared to reconstructions without downscatter compensation.

Conclusions:

• The developed model-based downscatter compensation is effective for quantitative 131I imaging.
• This method shows promise for enhancing accuracy in TRT treatment planning and dose verification.
• The technique may play a significant role in improving quantitative 131I imaging applications.