Optimizing single photon emission computed tomography protocols for accurate organ dode estimation in Lutetium- 177 peptide receptor Radionuclide therapy

This study explores two critical aspects of radionuclide molecular imaging within Peptide Receptor Radionuclide Therapy (PRRT) utilizing Lutetium-177 (Lu-177): quantitative imaging with Single Photon Emission Computed Tomography (SPECT) and the optimization of imaging protocols for accurate Absorbed Dose (AD) estimation. The investigation encompasses meticulous analyses f rom phantoms to patient studies, offering a comprehensive exploration of quantitative imaging with SPECT-CT. A noteworthy discovery in this research is the substantial reduction in the Calibration Factor (CF) as voxel volume decreases. The smallest volume (0.012 mL) yields the lowest CF of 80 cps/Bq. While opting for smaller voxel volumes, exemplified in the 0.012 mL case, enhances precision (lower SD), it compromises sensitivity (lower CF). This underscores the necessity for thoughtful consideration of voxel volume, sensitivity, and stability trade-off s when designing SPECT imaging protocols. In this study, the chosen voxel volume was 0.012 mL, and the identified lesion volume constituted around 28% of the maximum threshold. The initial phase of PRRT adopts a post-therapy approach, with this pilot study enrolling nine (9) patients deliberately selected by Nuclear Medicine Physicians based on suitability. The research demonstrates the feasibility of employing a single low-dose CT scan and three SPECT data points at 1, 24, and 72 hours for AD estimation in Organs at Risk (OARs) and Lesion Dose Per Administered Activity (LDpAs), suggesting good agreement with established methods. The study indicates an agreement with correlation coefficients for kidneys, spleen, liver, and bladder ranging f rom 0.8918 to 0.6292. The agreement of 0.7621 for LDpAs signifies a substantial level of concordance or correlation in the study's findings. In essence, the calculated lesion doses per administered activity using the proposed methodology align strongly with a correlation coefficient of 0.7621, demonstrating consistency and reliability compared to established methods. This reinforces confidence in the accuracy and precision of LDpAs measurements, providing a robust foundation for the methodology's validity in assessing and quantif ying lesion doses within the context of PRRT with Lu-177.

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