A need for eye lens dosimetry in nuclear medicine

Abstract

Background: Changing the individual dose limit for the lens of the eye from a value of 150 mSv per year to a level of 20 mSv (averaged over defined periods of five years or 50 mSv in a single year) means that issues related to routine eye lens dosimetry become interesting from the point of view of radiation protection. This could mean that the dosimeter designed to measure the doses at the level of the eye lens may become the next dosimeter routinely worn by nuclear medicine workers occupationally exposed to ionising radiation. The dosimeters currently used in nuclear medicine are the personal dosimeter and the ring dosimeter. Will this also be the case for nuclear medicine employees? In this interdisciplinary branch of medicine, the factors that cause the highest risk of radiation exposure of personnel are the process of manual handling, i.e. the process of preparing a radiopharmaceutical called labelling. Most of the radiopharmaceuticals used in nuclear medicine are labelled manually. In Poland, the exception from this rule is when radiopharmaceuticals are produced for the needs of positron emission tomography (PET), which are labelled using automatic processes. Manual procedures also include the process of radiopharmaceutical injection to the patients. The aim of the work was to assess the exposure of eye lenses of workers in nuclear medicine, as well as of the personnel in centers that produce radiopharmaceuticals for PET diagnostics, from the viewpoint of advisability of routine eye lens exposure monitoring, taking into account changes in the dose limit for the lens of the eye. Methods: The results of own measurements of the personal dose equivalent Hp(3), carried out in five nuclear medicine departments in Poland, as well as in two centers producing radiopharmaceuticals for PET, were subject to analysis. The analysis includes two most frequently used radionuclides for diagnostic purposes, namely 99mTc, 18F and the less frequently used 68Ga, in addition to 131I, which is used for therapeutic purposes. Dosimetric measurements were made using thermoluminescent detectors of domestic manufacture. Results & Conclusions: Estimated analysis of the annual exposure makes it possible to indicate cases where the maximum annual value of personal dose equivalent, in terms of Hp(3), exceeds threefold the new limit value specified at 20 mSv/year.