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

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 (¹⁸F) with Technetium-99m (^99mTc) in this test, and to indicate it with the lowest operational cost. The test was applied with sources of ^99mTc (62 GBq) and ¹⁸F (12 GBq), the activities of which were measured at different times, with the equipment preadjusted to measuring sources of ^99mTc, ¹⁸F, Gallium-67 (⁶⁷Ga), and Iodine-131 (¹³¹I). Over time, the average deviation between measured and expected activities from ^99mTc and ¹⁸F were, respectively, 0.56 (±1.79)% and 0.92 (±1.19)%. The average ratios for 99^mTc source experimental activity, when measured with the equipment adjusted for measuring ¹⁸F, ⁶⁷Ga, and ¹³¹I sources, in real values, were, respectively, 3.42 (±0.06), 1.45 (±0.03), and 1.13 (±0.02), and those for the ¹⁸F source experimental activity, measured through adjustments of ^99mTc, ⁶⁷Ga, and ¹³¹I, were, respectively, 0.295 (±0.004), 0.335 (±0.007), and 0.426 (±0.006). The adjustment of a simple exponential function for describing ^99mTc and ¹⁸F 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 ^99mTc, through being compatible with those acquired with ¹⁸F, 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 ¹⁸F, implies that ^99mTc should preferably be employed for linearity testing in clinics that normally use ¹⁸F, without the risk of prejudicing either the procedure itself or the guarantee of a high-quality nuclear medicine service