The impact of manipulating sestamibi doses on extremity radiation exposure.

Objectives Cardinal Health, the radiopharmacy serving Saint Joseph's Hospital, recently changed their unlimited free deliveries to three per day. Due to this change, more contingency stress doses (30mCi) of ^99mTc-Sestamibi for myocardial perfusion imaging (MPI) are being ordered to accommodate add-on MPI exams. These doses are adjusted to the correct dose by removing activity from the unit dose, either by drawing activity out of the syringe or by changing a needle. Saline may be added if the volume of the dose is very small. The purpose of this study is to determine if there is a significant increase in ring badge exposure rates due to adjusting sestamibi doses as compared to measuring the appropriately calibrated doses.

Methods Two months of exposure readings were obtained. Two ring badges were used for each month: one ring was worn when sestamibi doses needed to be altered and the other ring was worn to measure correctly calibrated unit doses. The average time to manipulate and/or measure a sestamibi dose and the number of doses measured for each ring were recorded. Ring badge readings were then evaluated.

Results Each manipulated dose resulted in an average exposure rate of 4.5 mrem whereas the average exposure rate of the appropriately calibrated unit dose was 0.08 mrem. On average, the technologist spent an additional 30 to 60 seconds handling the modified dose.

Conclusions Our current research shows that manipulation of a sestamibi dose increases the radiation exposure to a technologist’s ring badge. These exposure rates may vary depending on a technologist's experience, technique, and time spent manipulating the dose. Further collection of exposure rates on both dose sets is ongoing in order to solidify our research.