Preserving Preclinical PET Quality During Intratherapeutic Imaging in Radionuclide Therapy with Rose Metal Shielding Reducing Photon Flux

摘要

Performing PET imaging during ongoing radionuclide therapy can be a promising method to follow tumor response in vivo. However, the high therapeutic activity can interfere with the PET camera performance and degrade both image quality and quantitative capabilities. As a solution, low-energy photon emissions from the therapeutic radionuclide can be highly attenuated, still allowing sufficient detection of annihilation photons in coincidence. Methods: Hollow Rose metal cylinders with walls 2-4 mm thick were used to shield a Na-22 point source and a uniform phantom filled with F-18 as they were imaged on a preclinical PET camera with increasing activities of Lu-177. A mouse with a subcutaneous tumor was injected with F-18-FDG and imaged with an additional 120 MBq of Lu-177 and repeated with shields surrounding the animal. Results: The addition of Lu-177 to the volume imaged continuously degraded the image quality with increasing activity. The image quality was improved when shielding was introduced. The shields showed a high ability to produce stable and reproducible results for both spatial resolution and quantification of up to 120 MBq of Lu-177 activity (maximum activity tested). Conclusion: Without shielding, the activity quantification will be inaccurate for time points at which therapeutic activities are high. The suggested method shows that the shields reduce the noise induced by the Lu-177 and therefore enable longitudinal quantitative intratherapeutic imaging studies.