Dose Calibrator Linearity Testing: Radioisotope 99mTc or 18F? An Alternative for Reducing Costs in Nuclear Medicine Quality Control

Abstract

Dose calibrator linearity testing is indispensable for evaluating the capacity of this equipment in measuring radioisotope activities at different magnitudes, a fundamental aspect of the daily routine of a nuclear medicine department, and with an impact on patient exposure. The main aims of this study were to evaluate the feasibility of substituting the radioisotope Fluorine-18 ( ¹⁸ F) with Technetium-99m ( ^99m Tc) in this test, and to indicate it with the lowest operational cost. The test was applied with sources of ^99m Tc (62 GBq) and ¹⁸ F (12 GBq), the activities of which were measured at different times, with the equipment preadjusted to measuring sources of ^99m Tc, ¹⁸ F, Gallium-67 ( ⁶⁷ Ga), and Iodine-131 ( ¹³¹ I). Over time, the average deviation between measured and expected activities from ^99m Tc and ¹⁸ F were, respectively, 0.56 (+-1.79)% and 0.92 (+-1.19)%. The average ratios for 99 ^m Tc source experimental activity, when measured with the equipment adjusted for measuring ¹⁸ F, ⁶⁷ Ga, and ¹³¹ I sources, in real values, were, respectively, 3.42 (+-0.06), 1.45 (+-0.03), and 1.13 (+-0.02), and those for the ¹⁸ F source experimental activity, measured through adjustments of ^99m Tc, ⁶⁷ Ga, and ¹³¹ I, were, respectively, 0.295 (+-0.004), 0.335 (+-0.007), and 0.426 (+-0.006). The adjustment of a simple exponential function for describing ^99m Tc and ¹⁸ F experimental activities facilitated the calculation of the physical half-lives of the radioisotopes, with a difference of about 1% in relation to the values described in the literature. Linearity test results, when using ^99m Tc, through being compatible with those acquired with ¹⁸ F, imply the possibility of using both radioisotopes during linearity testing. Nevertheless, this information, along with the high potential of exposure and the high cost of ¹⁸ F, implies that ^99m Tc should preferably be employed for linearity testing in clinics that normally use ¹⁸ F, without the risk of prejudicing either the procedure itself or the guarantee of a high-quality nuclear medicine service.