Personal dosimetry for positron emitters, and occupational exposures from clinical use of gallium-68

Abstract

The current status and issues regarding positron dosimetry in nuclear medicine are summarized. The suitability of the UKHSA extremity and eye beta-gamma personal thermoluminescence dosemeters are then considered. Monte Carlo modelling is performed to determine their responses and derive sets of calibration factors, along with Hp(0.07) and Hp(3) conversion coefficients, for carbon 11, nitrogen 13, oxygen 15, fluorine 18 and gallium 68 sources, which are commonly used in PET-CT; data for these isotopes is assumed extrapolatable to other positron sources. It is found that the dosemeters are adequate for assessing exposures to PET radionuclides, even if their routine calibrations to caesium 137 were maintained. An idealized set of measurements representing gallium 68 exposure scenarios is then described, including reproducible mock-ups of individuals manipulating vials and syringes. Finally, a short case-study is presented that explores occupational doses during routine clinical use of gallium 68. The extremity dosemeter results demonstrated significant variations dependent upon the exposure conditions, with some seen to be comparatively large; whole-body and eye dose rates per activity were found to be lower. The importance of routine dose monitoring of workers is emphasized, with the need for a longer-termed follow-up study demonstrated.

Finger doses due to 68Ga-labelled pharmaceuticals in PET departments—results of a multi-centre pilot study

“…Applying the fingertip correction factor 4.3 to the normalised doses obtained in this study, results in a mean normalised fingertip dose of 2.1 mSv GBq −1 (SD of 2.5). In a recent study employing the use of fingerstall dosimetry, Eakins et al [23] measured normalised fingertip doses during three weeks in one hospital. A mean normalised dose of 0.16 mSv GBq −1 (SD of 0.07) was found for the medical physicists involved in the preparation and QC of 68 Ga-DOTATATE, while a mean normalised dose of 1.24 mSv GBq −1 (SD of 0.67) was found for the radiographers involved in the dispensing and administration of the same product.…”

Studies large and small: the Bernard Wheatley Award for 2022

“…Nuclear medicine has not featured strongly in our short-list this year. However, we published one important paper by Eakins et al (2022) on the dosimetry of the positron-emitting radionuclide Ga-68 that is being increasingly used to positron-emission tomography (PET), often incorporated into relatively new radiopharmaceuticals. The paper first addresses the more general issue as to whether existing thermoluminescent dosemeters are suitable for measuring personal doses from the positron-emitting radionuclides commonly used in PET-CT, considering the annihilation photons arising from each positron when it combines with an electron.…”