Quantitative Comparison of SPECT and PET Performance for Clinical Theranostic Applications.

Radiopharmaceutical therapy is an emerging approach to treat metastatic disease, with the potential to enable personalized care through imaging. With the growing interest in quantitative imaging, there remains a need for systematic assessment of imageable radionuclides and scanner performance under comparable conditions. This motivated us to quantitatively and qualitatively compare SPECT and PET performance using standardized evaluation procedures to assess their effectiveness in imaging applications for targeted radiotherapy.

Methods

The National Electrical Manufacturers Association International Electrotechnical Commission body phantom was used to assess recovery coefficients, contrast, and image quality, including spatial resolution and noise. SPECT performance was evaluated using 99mTc (a low-energy γ-ray-emitting isotope), 203Pb (a surrogate for the therapeutic α-particle-emitting 212Pb), and theranostic 177Lu. PET performance was tested using 18F, 89Zr, and 64Cu as imaging surrogates.

Results

PET demonstrated superior spatial resolution and accurate activity recovery compared with SPECT, which was limited by lower sensitivity, photon scatter, and collimator design constraints. Among PET isotopes, 18F showed consistently high quantitative accuracy, whereas 89Zr and 64Cu performed similarly, with only minor reductions in performance metrics. For SPECT, 99mTc outperformed 203Pb and 177Lu in both lesion detectability and activity recovery. 203Pb and 177Lu showed poor quantitative accuracy; however, increasing iterations in reconstruction improved results.

Conclusion

These findings underscore the importance of selecting appropriate imaging modalities, isotopes, and reconstruction parameters for theranostic applications. Limitations in quantitative accuracy must be addressed and acknowledged in the search for precise and effective treatment strategies. This study also demonstrates that 203Pb may serve as a suitable diagnostic partner to 212Pb and validates the use of these quantitative methodologies for the evaluation of PET and SPECT imaging tasks.