Development of 67Cu quantitative SPECT for clinical dosimetry

• Published in: The Journal of nuclear medicine (1978) Vol. 59; p. 1748
• Main Authors: Willowson, Kathy, Harris, Matt, Jeffery, Charmaine, Biggin, Colin, Hedt, Amos, Stoner, Jon, Bailey, Dale
• Format: Journal Article
• Language: English
• Published: New York Society of Nuclear Medicine 01-05-2018
• Subjects: Algorithms; Attenuation; Collimation; Collimators; Computed tomography; Diagnostic systems; Diameters; Dosimeters; Dosimetry; Image analysis; Image processing; Lesions; Medical imaging; Photopeak; Positron emission; Quantitative analysis; Radiation therapy; Radioisotopes; Recovery; Sensitivity; Single photon emission computed tomography; Somatostatin; Spatial discrimination; Spatial resolution; Tomography; United States > US
• ISSN: 0161-5505; 1535-5667

Objectives: ackground / Aims: Copper-67 (67Cu) shows promise as a radionuclide therapy agent, in particular when paired with the diagnostic PET imaging agent 64Cu. The aim of this work was to examine the potential of quantitative SPECT for 67Cu for the aim of clinical dosimetry in patients receiving 67Cu-SARTATE to treat somatostatin-positive neoplasia. Methods: All work was performed on an Intevo SPECT/CT (Siemens Healthineers, USA) using medium energy collimators and imaging the 185 keV photopeak (49% abundance) with a 20% energy window. Quantitative evaluation consisted of experimental work to model the transmission dependant scatter correction technique, camera specific sensitivity and dead time. Narrow-beam attenuation correction maps were derived based on a bi-linear relationship between CT number and material density. All corrections were implemented using in-house software written in IDL (Harris Geospatial, USA). Validation of quantitative accuracy was assessed with the IEC NEMA body phantom over a period of 7 days with decaying phantom activity (1.6 - 0.4 GBq) and a sphere-to-background ratio of 8:1. Results: Scanner sensitivity was measured as approximately 86 cps/MBq. The spatial resolution on planar imaging was found to be 2.8 cm. Nine SPECT/CT phantom acquisitions were acquired over a two week period, yielding an average difference between true and measured total phantom activity and measured background concentration of -2.1% and -1.7%, respectively. Figure 1 demonstrates the image analysis of the NEMA IEC Body Phantom to derive concentration recovery coefficients. The 37mm diameter sphere suffered from 20% count losses due to the partial volume effect (PVE) when using a threshold grown VOI to derive average hot-sphere concentration. The data suggest that underestimates to concentration, and so absorbed dose, can be expected in lesions of diameter less than 5cm. Conclusions: Quantitative SPECT and clinical dosimetry of 67Cu data is feasible and returns accurate measures in volumes unaffected by PVE. Small lesions can expect to under-estimate dose and would benefit from a resolution recovery algorithm to reduce partial volume losses.