Feasibility study of radioactivity estimation of 99mTc and 123I-labeled radiopharmaceuticals using shielded syringes.

This study investigates the feasibility of estimating the radioactivity of radiopharmaceuticals using shielded syringes. The radioactivities of ^99mTc-MDP, ^99mTc-HMDP, ^99mTc-ECD, ^99mTc-MAG₃, and ¹²³I-IMP were measured using a dose calibrator. Correlation coefficients and regression equations were obtained from the radioactivity in the shielded and unshielded syringes. ^99mTc-MDP was also measured for residual radioactivity after the administration. The correlation coefficients of ^99mTc-MDP, ^99mTc-HMDP, ^99mTc-ECD, ^99mTc-MAG₃, and ¹²³I-IMP were r_s = 0.9998, r_s = 0.9997, r_s = 0.9999, r_s = 0.9998, and r_s = 0.9888, respectively. The regression equations were y = 0.0364x + 0.0913, y = 0.0349x + 0.0273, y = 0.0343x - 0.0018, y = 0.0522x + 0.1215, and y = 0.0383x + 0.0058, respectively. The correlation coefficient for the residual radioactivity of ^99mTc-MDP was r_s = 0.9887 and the regression equation was y = 0.1505x + 0.0853. The radioactivity of ^99mTc- and ¹²³I-labeled radiopharmaceuticals in shielded syringes was accurately measured. It was suggested that the measuring shielded syringes could provide an estimate of the actual radioactivity.