Development and evaluation of an improved quantitative (90)Y bremsstrahlung SPECT method

Area of Science:

• Nuclear Medicine
• Medical Imaging
• Radiotherapy Physics

Background:

• Yttrium-90 (90Y) is vital for targeted radionuclide therapy (TRT).
• Direct imaging of 90Y is challenging due to its lack of gamma emissions, necessitating surrogate imaging agents.
• Accurate quantification of 90Y distribution is essential for effective TRT planning and dose verification.

Purpose of the Study:

• To develop and evaluate an improved quantitative single photon emission computed tomography (SPECT) reconstruction method for Yttrium-90 (90Y) bremsstrahlung photons.
• To address the challenges posed by the continuous and broad energy distribution of bremsstrahlung photons for accurate activity quantification.
• To enable direct imaging of 90Y distribution for improved TRT planning.

Main Methods:

• Developed a quantitative 90Y bremsstrahlung SPECT reconstruction method incorporating energy-dependent modeling of attenuation, scatter, and collimator-detector response.
• Utilized a validated Monte Carlo (MC) simulation (SIMIND code) with an experimentally estimated bremsstrahlung energy spectrum and decay-emission location model.
• Integrated an improved forward projection model into an ordered subsets-expectation maximization (OS-EM) iterative reconstruction algorithm.
• Validated the method using physical phantom experiments and realistic anatomical phantom simulations.

Main Results:

• Demonstrated excellent agreement between experimental measurements and MC simulations.
• The proposed method achieved significantly higher accuracy in modeling photon counts (-1.1% error) compared to previous methods (>20% error).
• Achieved excellent quantitative accuracy for organ activity estimates (-1.6% to 11.9% error), comparable to results for Iodine-131 (131I).

Conclusions:

• The developed 90Y bremsstrahlung SPECT reconstruction method provides highly accurate organ activity estimates.
• The accuracy achieved approaches that previously observed for 131I, indicating significant improvement.
• This method holds potential for verifying organ doses in 90Y-based targeted radionuclide therapy.