Evaluations for Determination of Optimum Shields in Nuclear Medicine

Background: ¹³¹I source is widely used in the treatment of hyperthyroidism and thyroid cancers. ¹³¹I emits both beta and gamma-rays. Radiation protection is considered for gamma rays emitted by ¹³¹I. It seems no special shield against ¹³¹I source to be designed.

Objective: This research aims to evaluate determination of optimum shields in nuclear medicine against ⁹⁹Tc^m and ¹³¹I sources by dosimetric method. Additionally, Monte Carlo simulation was used to find the optimum thickness of lead for protection against ¹³¹I source.

Material and methods: This is an experimental research in the field of radiation protection. A calibrated model of GraetzX5C Plus dosimeter was used to measure exposure rates passing through the shields. The efficiency of the shields was evaluated against ⁹⁹Tc^m and ¹³¹I. Furthermore, Monte Carlo simulation was used to find the optimum thickness of lead for protection against ¹³¹I source.

Results: The findings of the dosimetric method show that the minimum and maximum efficiencies obtained by the lead apron with lead equivalent thickness of 0.25 mm and the syringe holder shields with thickness of 0.5 mm lead were 50.86% and 99.50%, respectively. The results of the simulations show that the minimum and maximum efficiencies obtained by lead thicknesses of 1 mm and 43 mm were 19.36% and 99.79%, respectively.

Conclusion: The optimum shields against ⁹⁹Tc^m are the syringe holder shield, the tungsten syringe shield, and the lead partition, respectively. Furthermore, based on simulations, the thicknesses of 11-28 mm of lead with efficiencies between 90.6% to 99% are suggested as the optimum thicknesses to protect against ¹³¹I source.