Radiation exposure assessment of tungsten vial shields vs. lead glass vial shields.

Objectives: Vial shields are an essential component of the radiation safety program in any nuclear pharmacy or nuclear medicine hot lab. Northwestern Memorial Hospital’s standard practice is to use commercially available lead glass vial shields when reconstituting technetium 99m (Tc-99m). As high activity Tc-99m sestamibi kits are prepared on a daily basis, the objective of this study is to evaluate the radiation shielding properties of two commercially available vial shields from Biodex Medical Systems.

Methods: The Biodex High Density Lead Glass Vial Shield (001-075) was evaluated by adding 1,421 mCi of Tc-99m into a 10 mL sterile vial. The Biodex Tungsten Vial Shield (053-805) was evaluated by adding 1,428 mCi of Tc-99m into a 10 mL sterile vial. Measurements were recorded using a Fluke 451B ion chamber to determine the radiation exposure on the surface of both shielding configurations. Following the exposure readings, a thermoluminescent dosimeter (TLD) was placed on each vial shield for 30 minutes. The tungsten shield and the lead glass shield contained 1,404 mCi and 1,405 mCi of Tc-99m, respectively, at the time the TLDs were placed. Following a 30 minute exposure time, TLDs were removed and sent to Landauer for processing and analysis. Results: Ion chamber readings taken at the surface of both the tungsten and lead glass shields were 0.360 mR/h and 13.7 mR/h, respectively. Based on these measurements, the tungsten shield resulted in a 97.4% reduction in surface exposure compared to the lead glass shield. The TLD analysis from Landaur reported “M” (dose equivalents below the minimum measurable quantity of 10 mrem) for the tungsten shield, and 60 mrem exposure for the lead glass shield.

Conclusions: The results demonstrate that tungsten shielding significantly reduces radiation exposure when compared to lead shielding. Based on these findings, Northwestern Memorial Hospital has implemented the use of tungsten vial shields for high activity Tc-99m preparations to minimize radiation exposure and adhere to the ALARA principle.