About the requirements of regular monitoring of doses for the eye lens of the staff working with radiopharmaceuticals

In 2011 the International Commission on Radiation Protection established the threshold value of the absorbed dose in the lens of the eye for the development of cataract equal to 0.5 Gy for acute and chronic exposure. A dose limit for exposure of the lens of the eye was established equal to 20 mSv per year, averaged over five consecutive years (100 mSv over 5 years), and 50 mSv for any single year. The Russian regulatory documents specify the dose limit for the exposure of the eye lens equal to 150 mSv per year and there are noclear criteria determining the conditions under which it is necessary to carry out individual monitoring of exposure of the eye lens, but it should be expected that in Russia the dose limit will also be reduced in the coming years. Objectives of the study: assessment of the absorbed doses in the eye lenses of the staff of medical facilities working with radiopharmaceuticals; identification of the relationship between the absorbed dose in the eye lens and the type and range of activities of the radionuclides; justification of the feasibility and identification of categories of staff for regular individual monitoring of the eye lens doses in nuclear medicine departments. Within the framework of the study, the absorbed dose in the eye lens for staff members working with the radiopharmaceuticals in nuclear medicine departments of two medical facilities in St. Petersburg were measured, the possibility of detection of high eye lens doses for these workers was analyzed. The monitoring period was set to 1 month. The workers were divided into two groups depending on the type of radionuclides in the radiopharmaceuticals they commonly work with: 1) the staff of the PET departments and the radiochemistry units working the with radiopharmaceuticals labeled with positron emitting radionuclides (11C, 18F, 68Ga) 2) the staff of the departments of nuclear medicine working with radiopharmaceuticals labeled with 89Sr, 99mTc. Measurements of the operational quantity Н (3 ) were carried out by the method o f thermoluminescent dosimetry. We used individual dosimeters that met the conditions for determining the operating values. Dosimeters designed to measure Н (3) were located on the collar of a dressing gown without an attenuator. The results of measurements of Н (3 ) indicated that the collected dose depends on the type of the work, the equipment of the nuclear medicine unit, the radionuclide and its activity both at the workplaces and for the entire period of data collection. High dose values were obtained for procedural nurses, radiochemists and technologists who worked with positron-emitting radionuclides (18F, 68Ga and 11C), which, when extrapolated to a year, can exceed 20 mSv. For this category of workers, it is advisable to carry out individual monitoring of external irradiation of the eye lenses after a preliminary assessment of the level of exposure of workers and an assessment of the risks of high doses of the eye lens.