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RADIOPHARMACY

Determination of the Efficiency of Commercially Available Dose Calibrators for -Emitters
Jean-Francois Valley, PhD; Shelley Bulling; Michel Leresche; and Claude Wastiel ¸
Institute for Applied Radiophysics, Lausanne, Switzerland

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 behavelike -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 low- and high-energy -emitters, the use of manufacturer-supplied calibration factorsintroduces significant measurement inaccuracy. Key Words: dose calibration; -emitters; radiation therapy; palliation J Nucl Med Technol 2003; 31:27–32

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For correspondence or reprints contact: Jean-Francois Valley, PhD, ¸ Institut de Radiophysique Appliquee, Grand-Pre 1 CH-1007, Lausanne, ´ ´ Switzerland. E-mail: Jean-Francois.Valley@inst.hospvd.ch

he analgesic radiation therapy of bonemetastasis calls for -emitting radionuclides able to concentrate at the site of bone repair and deliver a dose sufficient for pain palliation for a period of time (1). Dosimetry of these radionuclides is difficult because of the complex geometry of bone marrow and the variability of uptake. The aim of this palliative therapy is not to deliver the highest possible dose to the tumor but to obtain areduction in bone pain. The principal limiting factor for therapy is the depression of bone marrow activity. Doses delivered are much lower than those in conventional radiation therapy, and standardized activities based on clinical experience are used. Before treatment, the activity to be delivered to the patient must be checked. This measurement is performed in a dose calibrator with the radionuclide ineither the manufacturer’s glass vial or, preferably, in the syringe to be used for injection. Dose calibrator sensitivity has been studied extensively (2,3). Commercially available calibrators are supplied with calibration factors for commonly used -emitting radionuclides. However, some problems have been reported in the accuracy of these factors, and Zimmerman and Cessna (4) reported errors ofabout 10% for positron emitters. In addition, the presence of low-energy x- or -ray components can introduce a high dependence of dose calibrator sensitivity on measurement geometry because of the high attenuation between the source and the sensitive volume. The use of a copper filter to absorb low-energy radiation and stabilize calibrator response has been proposed (5). Radiopharmaceuticals used...