Quantitative accuracy of (177)Lu SPECT reconstruction using different compensation methods: phantom and patient...

Area of Science:

• Nuclear Medicine
• Medical Imaging
• Radiotherapy Physics

Background:

• Accurate quantification in targeted radionuclide therapy (TRT) using SPECT/CT is crucial for optimizing radiation dose to tumors and healthy tissues.
• Ordered subset expectation maximization (OSEM) is commonly used for SPECT/CT image reconstruction, often with attenuation (A), scatter (S), and detector/collimator response (R) compensation methods.
• This study investigates the impact of different compensation method combinations on (177)Lu quantification accuracy.

Purpose of the Study:

• To evaluate the effect of various compensation methods (A, AR, ARS) on quantitative accuracy in SPECT/CT imaging of (177)Lu.
• To assess the impact of these compensation methods on absorbed dose estimations in the kidneys for patients undergoing (177)Lu-DOTATATE treatment.
• To determine the optimal compensation strategy for improving tumor dosimetry in (177)Lu-based peptide receptor radionuclide therapy (PRRT).

Main Methods:

• An anthropomorphic torso phantom with spherical inserts of varying sizes (0.4-104.4 cm³) containing known (177)Lu activity was imaged.
• SPECT/CT images were reconstructed using the OSEM algorithm with attenuation (A), attenuation and response (AR), and attenuation, response, and scatter (ARS) compensation.
• Concentration recovery coefficients (cRC) were calculated for each insert, and absorbed doses to the kidneys were estimated from post-therapy dosimetry acquisitions of ten (177)Lu-DOTATATE-treated patients.

Main Results:

• Attenuation, response, and scatter (ARS) compensation yielded significantly higher concentration recovery coefficients (cRC) compared to attenuation correction alone, especially for smaller inserts.
• The inclusion of collimator and detector response (R) improved cRC for a 1.3-cm insert from 0.19 to 0.43.
• Patient data showed that AR and ARS compensation resulted in 15-25% higher kidney absorbed dose estimates compared to attenuation correction alone.
• Effective half-life decay estimations showed no significant difference between compensation methods.

Conclusions:

• Applying attenuation, response, and scatter (ARS) compensation during OSEM reconstruction maximizes quantitative accuracy (cRC) in SPECT/CT imaging of (177)Lu.
• ARS compensation demonstrates particular benefit for quantifying small-sized sources, potentially improving tumor dosimetry in (177)Lu PRRT.
• Increased absorbed dose estimates to organs like the kidneys highlight the importance of comprehensive compensation methods in patient dosimetry.