科研之友
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摘要
Cyclotron production of Tc-99m through the Mo-100(p,2n)Tc-99m reaction channel is actively being investigated as an alternative to reactor-based Mo-99 generation by nuclear fission of U-235. Like most radioisotope production methods, cyclotron production of Tc-99m will result in creation of unwanted impurities, including Tc and non-Tc isotopes. It is important to measure the amounts of these impurities for release of cyclotron-produced Tc-99m (CPTc) for clinical use. Detection of radioactive impurities will rely on measurements of their gamma (gamma) emissions. Gamma spectroscopy is not suitable for this purpose because the overwhelming presence of Tc-99m and the count-rate limitations of gamma spectroscopy systems preclude fast and accurate measurement of small amounts of impurities. In this article we describe a simple and fast method for measuring gamma emission rates from radioactive impurities in CPTc. The proposed method is similar to that used to identify Mo-99 breakthrough in generator-produced Tc-99m: one dose calibrator (DC) reading of a CPTc source placed in a lead shield is followed by a second reading of the same source in air. Our experimental and theoretical analysis show that the ratio of DC readings in lead to those in air are linearly related to gamma emission rates from impurities per MBq of Tc-99m over a large range of clinically-relevant production conditions. We show that estimates of the gamma emission rates from Tc impurities per MBq of Tc-99m can be used to estimate increases in radiation dose (relative to pure Tc-99m) to patients injected with CPTc-based radiopharmaceuticals. This enables establishing dosimetry-based clinical-release criteria that can be tested using commercially-available dose calibrators. We show that our approach is highly sensitive to the presence of Tc-93g, Tc-93m, Tc-94g, Tc-94m, Tc-95m, Tc-95g, and Tc-96g, in addition to a number of non-Tc impurities.
- 出版日期2015-11-7
