A phantom-based method to standardize dose-calibrators for new β+-emitters

Quantitative imaging with PET requires accurate measurements of the amount of radioactivity injected into the patient and the concentration of radioactivity in a given region. Recently, new positron emitters, such as I, Zr, Rb, Ga, and Cu, have emerged to promote PET development, but standards are still largely lacking. Therefore, we propose to validate a simple, robust, and replicable methodology, not requiring the use of any standards, to accurately calibrate a dose-calibrator for any β-emitter. On the basis of F cross-calibration, routinely performed with fluorine-18-fluorodeoxyglucose (F-FDG) in nuclear medicine departments, a methodology was developed using β-emitting’ phantoms to cross-calibrate the dose-calibrator for measuring the activity of positron emitters and quantifying the standardized uptake value (SUV). Ga phantoms filled with activities measured with various dose-calibrator settings were imaged to establish calibration curves (SUV values as a function of the dose-calibrator settings) and to identify the setting value, yielding an SUV value of 1.00 g/ml, reflecting an accurate measurement of Ga activity. Activities measured with the identified setting were finally checked with a γ-counter. The setting of 772±1 was identified as ensuring that the studied dose-calibrator is correctly calibrated for Ga to ensure an SUV value of 1.00±0.01 g/ml. γ-Ray spectrometry confirmed the accurate measurement of Ga activities by the dose-calibrator (relative error of 2.9±1.5%). We have developed a phantom-based method to accurately standardize dose-calibrators for any β-emitter, without any standards.