Dose rates in nuclear medicine and the effectiveness of lead aprons: updating the department’s knowledge on old and new procedures

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Abstract

Introduction

Answers to common nuclear medicine radiation safety questions often involve the consideration of dose rates from injected patients and the inverse square law. For staff, lead aprons are available as an option, although they are not routinely used and their effectiveness varies depending on the isotope. New tests and procedures have been introduced at this hospital, including PET and 90Y microsphere implantation, which have required a review and investigation of their potential impact on staff doses. To answer these questions and to account for the recently introduced technologies and procedures, a study was conducted to measure and demonstrate the level of effectiveness of the department’s lead aprons and to simulate patient dose rate measurements and estimations by obtaining measurements from water phantoms filled with these isotopes.

Materials and methods

A calibrated survey meter was used to measure dose rates at varying distances from water phantoms filled with 99mTc, 67Ga, 131I, 18F and 90Y. Thermoluminescence dosimeters attached to an anthropomorphic phantom with a lead apron were used to assess the effectiveness of the lead aprons available within the department. An uncollimated detector from a gamma camera was used to observe the changes to the energy spectrum in the presence of the lead apron.

Results

The results from the dose rate measurements demonstrated an overestimation by the inverse square law at close distances. This overestimation can be in excess of four times the measurements made within this study. The use of a lead apron was shown to reduce doses by varying degrees depending on the isotope used. A 64.5% dose reduction was observed when shielding against 99mTc with diminishing effectiveness against the remaining isotopes. The results for 90Y suggest that using a lead apron could result in dose escalation at shallow depths.

Conclusion

A table of conversion factors, independent of the isotope, was generated for the estimation of dose rates from injected patients at various distances. An isotope-specific conversion table was also generated. The effectiveness of the lead aprons within the department was also successfully measured and assessed and recommendations were passed on to staff regarding their use.

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