Accuracy of ¹⁷⁷Lu activity quantification using MCNP5-Modeled SPECT imaging.

Area of Science:

• Nuclear Medicine
• Medical Physics
• Radiopharmaceutical Therapy

Background:

• Accurate quantification of radiopharmaceuticals like Lutetium-177 (¹⁷⁷Lu) is crucial for effective radionuclide therapy and dosimetry.
• Monte Carlo simulations offer a powerful tool for modeling complex imaging physics, but require rigorous validation.

Purpose of the Study:

• To assess the accuracy of ¹⁷⁷Lu quantification using the Monte Carlo N-Particle Transport Code, Version 5 (MCNP5).
• To establish a reliable framework for activity quantification in ¹⁷⁷Lu SPECT imaging through code validation.

Main Methods:

• Verified MCNP5 code against experimentally measured calibration factors (CF) using two phantom configurations.
• Modeled a uniform ¹⁷⁷Lu concentration in a Petri dish and a spherical source in a Jaszczak phantom to determine CF₁ and CF₂.
• Evaluated quantification error using recovery coefficients (RC) in a NEMA phantom.

Main Results:

• Determined calibration factors CF₁ (12.5 ± 1.5 cps/MBq) and CF₂ (16.0 ± 2.0 cps/MBq).
• Observed a significant difference (21.26%) between CF₁ and CF₂, highlighting the impact of phantom geometry.
• Demonstrated that MCNP5 simulations accurately account for photon attenuation and scatter.

Conclusions:

• MCNP5 provides a reliable framework for accurate ¹⁷⁷Lu activity quantification in SPECT imaging.
• The simulation code effectively models SPECT imaging processes, crucial for dosimetry.
• Findings support the use of MCNP5 for improved dosimetry calculations in ¹⁷⁷Lu radionuclide therapy.