ASSESSMENT OF THE LOCAL EXPOSURE OF SKIN ON HANDS OF NUCLEAR MEDICINE WORKERS HANDLING 18F-LABELLED RADIOPHARMACEUTICALS: PRELIMINARY CZECH STUDY

A simple, reliable and accurate approach for assessing [131I]-capsule activity leading to significant reduction of radiation exposure of medical staff during radioiodine therapy

PURPOSE

According to German law, the [¹³¹I]-capsule activity has to be checked in the context of radioiodine therapy (RIT) immediately before application. The measurement leads to significant radiation exposure of the medical personnel, especially of their hands. We aimed to establish a method for estimating [¹³¹I]-capsule activity by measuring the dose rate (DR) at contact of the delivered lead closed container carrying the [¹³¹I]-capsules and to evaluate radiation exposure in comparison to conventional [¹³¹I]-capsule measurement using a dose calibrator.

METHODS

DR on the surface of the closed lead container was measured at two locations and correlated linearly with the [¹³¹I]-capsule activity measured in a dose calibrator to create calibrating curves. The hand and whole body (effective) doses were determined with official dose meters during validation of our method in clinical practice.

RESULTS

The determination coefficients (R²) of linear calibration curves were greater than 0.9974. The total relative uncertainty for estimating [¹³¹I]-capsule activity with our method was <±7.5% which is lower than the uncertainty of the nominal activity and quite close to the threshold limit for the maximum allowed uncertainty of ± 5% for measuring activity in radioactive drugs. The reduction of the hand dose caused by our method was 97% compared with the conventional measurements of the [¹³¹I]-capsules in a dose calibrator.

CONCLUSION

Measuring DR on the surface of the closed lead containers enables the [¹³¹I]-capsules activity to be estimated simply, reliably and with sufficient accuracy leading to significant reduction of the radiation exposure for the medical staff.

Review of extremity dosimetry in nuclear medicine

The exposure of the fingers is one of the major radiation protection concerns in nuclear medicine (NM). The purpose of this paper is to provide an overview of the exposure, dosimetry and protection of the extremities in NM. A wide range of reported finger doses were found in the literature. Historically, the highest finger doses are found at the fingertip in the preparation and dispensing of¹⁸F for diagnostic procedures and⁹⁰Y for therapeutic procedures. Doses can be significantly reduced by following recommendations on source shielding, increasing distance and training. Additionally, important trends contributing to a lower dose to the fingers are the use of automated procedures (especially for positron emission tomography (PET)) and the use of prefilled syringes. On the other hand, the workload of PET procedures has substantially increased during the last ten years. In many cases, the accuracy of dose assessment is limited by the location of the dosimeter at the base of the finger and the maximum dose at the fingertip is underestimated (typical dose ratios between 1.4 and 7). It should also be noted that not all dosimeters are sensitive to low-energy beta particles and there is a risk for underestimation of the finger dose when the detector or its filter is too thick. While substantial information has been published on the most common procedures (using^99mTc,¹⁸F and⁹⁰Y), less information is available for more recent applications, such as the use of⁶⁸Ga for PET imaging. Also, there is a need for continuous awareness with respect to contamination of the fingers, as this factor can contribute substantially to the finger dose.