A fast and simple dose-calibrator-based quality control test for the radionuclidic purity of cyclotron-produced 99mTc. (9th October 2015) - Tanguay, J
Abstract: Cyclotron production of Tc through the 100 Mo(p, 2n) Tc reaction channel is actively being investigated as an alternative to reactor-based 99 Mo generation by nuclear fission of 235 U. Like most radioisotope production methods, cyclotron production of Tc 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 (CPTc) for clinical use. Detection of radioactive impurities will rely on measurements of their gamma ( γ ) emissions. Gamma spectroscopy is not suitable for this purpose because the overwhelming presence of Tc and the count-rate limitations of γ spectroscopy systems preclude fast and accurate measurement of small amounts of impurities. In this article we describe a simple and fast method for measuring γ emission rates from radioactive impurities in CPTc. The proposed method is similar to that used to identify 99 Mo breakthrough in generator-produced Tc: 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 γ emission rates from impurities per MBq of Tc over a large range of clinically-relevant production conditions. We show that estimates of the γ emission rates from Tc impurities per MBq of Tc can be used to estimate increases in radiation dose (relative to pure Tc) 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, Tc, Tc, Tc, Tc, Tc, and Tc, in addition to a number of non-Tc impurities.