Procedure of Monitoring of Internal Exposures

For the handling of sources of ionising radiation, dose limits for the workers have been laid down in the Radiation Protection Act (Strahlenschutzgesetz - StrlSchG). For work-related exposure to ionising radiation the limit value of the effective dose is 20 mSv per calendar year. When handling unsealed radioactive substances, the body dose can be composed of external and/or internal radiation exposure, depending on working conditions, the chemical form of the used substances and the type of radionuclides.

Internal exposure occurs always when radionuclides have entered the body, this is referred to as incorporation. The activity taken into the body by inhalation or ingestion must not result in exceeding the dose limits (effective dose or organ dose, respectively) of the StrlSchG. Neither must these dose limits be exceeded by the sum of the contributions of internal and external radiation exposure. The Radiation Protection Act is complemented by the Radiation Protection Ordinance (Strahlenschutzverordnung - StrlSchV) on Protection against the Harmful Effects of Ionising Radiation.

Methods and competences

The monitoring of internal exposures is regulated in the German Guideline of Physical Radiation Protection Control. The following monitoring methods for the determination of the incorporated activity are commonly used:

• In-vivo methods: Determination of the activity of radionuclides in the body or in the organs
• In-vitro methods: Determination of the activity concentration of radionuclides in biological samples (urine, faeces)
• Room-air measurements: Determination of the activity concentration of radionuclides in the air at the workplace.

The first two methods are carried out by approved laboratories responsible for monitoring internal exposures (ALMIEs). These laboratories are accredited by the respective competent German Federal States authorities. The third method is used when the first two methods are not suitable. This is the case if, e.g., the radionuclides to be monitored are too short-lived or the methods are not sensitive enough. In this case the responsible radiation protection supervisor and/or the radiation protection officer at the site allows taking appropriate actions.

Tasks of Monitoring Internal Exposures

It is the task of monitoring internal exposures to assess retrospectively if occupationally exposed workers have incorporated radioactive substances. The possibly incorporated activity is determined and the body dose resulting from this intake is assessed using the monitored data. This means that monitoring internal exposures, based on measurements, serves to determine retrospectively a radiation exposure.

The Coordinating Office for Internal Monitoring

Since 1996, the Coordinating Office for Internal Monitoring of the Federal Office for Radiation Protection (BfS) has assumed the responsibility for monitoring internal exposures. The Coordinating Office is responsible for all principal and special questions concerning monitoring of internal exposures not covered by the German Federal States. The spectrum of information and consultancy comprises both the determination of activity in the respective medium (body, urine, faeces etc.) and the corresponding dose assessment.