Determination of the Efficiency of Commercially Available Dose Calibrators for -Emitters

Objectives: The goals of this investigation are to determine whether commercially available dose calibrators can be used to measure the activity of -emitting radionuclides used in pain palliation and to establish whether manufacturer-supplied calibration factors are appropriate for this purpose. Methods: Six types of commercially available dose calibrators were studied. Dose calibrator response was controlled for 5 -emitters used for calibration or typically encountered in routine use. For the 4 most commonly used -emitters (32P, 90Sr, 90Y, and 169Er) dose calibrator efficiency was determined in the syringe geometry used for clinical applications. Efficiency of the calibrators was also measured for 153Sm and 186Re, 2 -emitters with significant -contributions. Source activities were traceable to national standards. Results: All calibrators measured -emitters with a precision of 10%, in compliance with Swiss regulatory requirements. For -emitters, dose calibrator intrinsic efficiency depends strongly on the maximal energy of the -spectrum and is notably low for 169Er. Manufacturer-supplied calibration factors give accurate results for -emitters with maximal -energy in the middle-energy range (1 MeV) but are not appropriate for use with low-energy (169Er) or high-energy (90Y) -emitters. -emitters with significant -contributions behave like -emitters. Conclusion: Commercially available dose calibrators have an intrinsic efficiency that is sufficient for the measurement of -emitters, including -emitters with a low maximum -energy. Manufacturer-supplied calibration factors are reliable for -emitters and -emitters in the middle-energy range. For lowand high-energy -emitters, the use of manufacturer-supplied calibration factors introduces significant measurement inaccuracy.