Objective To analyze the radiation-exposure dose of non-nuclear medical staff from patients who had undergone ⁹⁹Tc^m-MDP administration for whole-body bone scan.

Methods From August 2018 to January 2019, 51 subjects who had undergone whole-body bone scan in our department were selected. The subjects were injected with 925 MBq ⁹⁹Tc^m-MDP and had drunk 1000 mL of water. They were divided into two groups, namely, micturition and non-micturition groups within 0.5 h. The equivalent dose rates of external radiation 0.5, 1, 2, 4, and 6 m away from the head or abdomen of the subject were measured at 0.5, 1, 2, 3, 4, and 6 h after ⁹⁹Tc^m-MDP injection and water drinking by using an χ, γ dosimeter. The Mann-Whitney U test of two independent samples was used to compare two groups. Repeated-measurement ANOVA was used to compare different times and distances of multiple measurements. The nonparametric Wilcoxon Z test was used for paired samples.

Results The radiation equivalent dose rates of 0.5, 1, 2, 4, and 6 m in the urination group were significantly lower than those in the non-urination group (40.29±4.67) μSv/h vs. (77.29±10.71) μSv/h, (15.22±1.64) μSv/h vs. (29.48±4.56) μSv/h, (4.15±0.47) μSv/h vs. (7.45±1.07) μSv/h, (1.32±0.10) μSv/h vs. (2.63±0.31) μSv/h, (0.45±0.05) μSv/h vs. (0.78±0.15) μSv/h, and the differences were statistically significant (Z=5.197, 5.148, 5.251, 5.199, and 5.202, respectively; all P<0.001). The radiation equivalent dose rates of the abdominal or head level in the urination group decreased rapidly with prolonged time (F=5397.675 and 4834.512, respectively; both P<0.001) and with increased distance (F=3459.712 and 3105.426, respectively; both P<0.001), and the differences were statistically significant. Meanwhile, the cumulative equivalent dose increased with prolonged time and decreased distance. Compared with the 6 h cumulative dose equivalent (148.51±13.83) μSV at 0.5 m of abdominal horizontal distance in urination group, the 6 h cumulative dose equivalent (55.85±5.22) μSV at 1 m of abdominal horizontal distance in urination group decreased significantly (Z=5.610, P<0.001). Compared with the 6 h cumulative dose equivalent (132.74±12.95) μSV at 0.5 m of head horizontal distance in urination group, the 6 h cumulative dose equivalent (49.88±4.72) μSV at 1 m of head horizontal distance in urination group decreased significantly (Z=5.438, P<0.001). The cumulative dose equivalent in urination group increased with the extension of irradiation time and decreased with the increase of distance.

Conclusion The external exposure dose of ⁹⁹Tc^m-MDP from patients awaiting whole-body bone scan was far less than the limitation (≤1 mSv/year per individual) set by domestic and international legal rules for non-nuclear medical staff. Most of the exposure risks of non-nuclear medicine staff to ⁹⁹Tc^m-MDP from patients could be avoided by staying more than 1 m from the patient 3 h after injection.