Assessment of occupational exposure

The legal basis for radiation protection of radiation workers was established according to the IAEA, ICRP, EC and other international requirements and recommendations. The requirements for occupational monitoring of occupational exposure are determined by these documents:

Lithuanian Hygiene Standard. The Basic Radiation Protection Standards, (2001);

Lithuanian Hygiene Standard. Requirements for monitoring of internal exposure, (2001) Lithuanian Hygiene Standard. Radiation Protection and Safety of Outside Workers, (1999);

The Order of Monitoring of Workers Exposure and Workplaces, (2007).

System of monitoring of occupational exposure was created in the regulatory authority in radiation protection in country – in the Radiation Protection Centre (RSC). The data of individual occupational doses are collected in the State Registry of ionizing radiation sources and doses of radiation workers. The RSC operates the State Register of occupational exposure doses, which has been established in 1999.

The personal dosimetry laboratory at the Radiation Protection Centre provides individual monitoring of 3000 workers from the whole country working in medicine, industry and research. It is accredited according the ISO 17025 by Lithuanian National Accreditation Bureau since 2004.

This service operates since 1991. Before it only separate licensees were running their own personal dosimetric systems, based mainly on film dosimeters. The "Rados" TLD system is used for measurements of external doses to whole body and extremities. The "Rados" system is also used for evaluation of patients’ doses in selected hospitals.

The operational dose quantities used for external exposure are the personal dose equivalent Hp(10) and Hp(0.07). Minimal registered dose is – 0.01mSv.

The dosimetric service recently provides individual monitoring of about 3000 workers of medicine, industry, science and research. Doses of outside workers are monitored, as well.

Period of monitoring is 3 months though in some cases (interventional radiology, industrial radiography) measurements of accumulated doses are performed once per month. The average occupational exposure dose was about the 0,27 mSv for medical workers, 0,36 mSv for industrial workers and 0,1 mSv research workers in 2007. Detailed analysis of doses received by different categories of workers is performed. System of urgent review of work conditions in case of increased dose is set.

Assessment of internal exposure

Equipment and techniques are available in Lithuania for measurement of internal contamination. A whole body counter with Ge detector and NaI thyroid counter are available at the Radiation Protection centre since 2004. Using these techniques there are performed internal exposure measurements of nuclear medicine workers and public.

Bioassay measurements started at the Radiation Protection Centre in 1999. Urine samples are analysed by means of gamma spectrometry, liquid scintillation counting and measurements of gross activity. Determination of activity of uranium and plutonium by alpha spectrometry is also available. All this equipment can be used under accidental conditions.

For internal dose assessment the IMBA and LUDEP software packages are used.
The more detailed information about occupational exposure monitoring is set in annual reports of Radiation protection centre.