Clinical Radioprotection

Controlled and Supervised areas

            A controlled area is an area in which specific protection and safety measures are required for controlling exposures or preventing contamination during working conditions, preventing the extent of exposures. A supervised section is an area with reviewed working conditions without specific procedures. A controlled area is often within a supervised area, but need not necessarely be so.

            In a controlled area the annual  dose could exceed 5 msV or 30% of the equivalent dose for crystalline, skin or extremities, labeled with green color. This area may have within it, sections with limited stay, regulated or forbbiden access, according to the risk level. They are usually associated to yellow, orange or red color, respectively.

            In a supervised area the annual dose could exceed 1 msV or 10% of the equivalent dose for crystalline, skin or extremities. It is usually associated to gray color.

Exposed Personnel

        Anyone working in a nuclear medicine laboratory must be licensed in the use of radioactivity with especial training in order to well understand the benefits and adverse effects of ionizing radiation. It is essential to take a specific training course, including radioprotection concepts. The use of a dosimeter is mandatory to measure constantly the exposure dose and to receive their lectures every 2 or 3 months. Written records must be kept separate for each of the institutions where the professional works. It is important to be aware of the country limits and maximun exposure doses. A typical level is to consider 50 mSv (5 rem) as the maximun cumulative amount to receive in 1 year. If that amount is exceeded, then the employee should start working in an area not exposed to ionizing radiations up until to catch up with the allowed doses per year. A pregnant worker should be considered as a member of the public and the exposure dose during the complete pregnancy period be kept below 1 mSv.

Dosimetry

            Personal Dosimetry has two aspects: 1) Control and measurement of radiation doses received by externally and 2) Control and measurement of the dose received internally, which will be discussed separately.

            The doses received externally by personnel and in some especial cases by patients can be measured with devices that are sensitive enough to detect levels used in daily activities in nuclear medicine. Those are the dosimeters and which are described below.

Dosimeter Types:

a) Film Dosimeter

            The principle used with this dosimeter, is the exposure of a photographic emulsion to the radiation, followed by the development of the film, and evaluation of the degree of darkening by densitometry. This fact allows to evaluate the absorbed dose, after a pre-calibration for each type of film. Photographic dosimeters consist of a special film wrapped in an opaque paper bag, mounted on a small case provided with a clamp, which allows the instrument to be attached to  the gown, lead apron or any work clothing . The support frame is provided with a series of screens and filters which allow simultaneous determination of a series of radiological data of interest.
Different types of film can cover relatively large margins different doses. The most used typically cover between 0.1 mSv and 10 mSv and 10 mSv and  1 Sv. For especial measurements it can be utilized films that reach as much as 10 Sv.  In the management of photographic dosimeters one has to be aware of certain precautions. For example, the photographic plates have an aging process with storage time, which skews in excess dose values registered. If the film experiences the effects of high temperature or the action of certain vapors, you may experience  spurious uncontrolled darkening  after development, and consequently to an erroneous increase in the measurements.
As a main advantage with film dosimetry it provides a permanent record of the dosimetric information as developed film can be archived and be part of dosimetry history of the worker. In contrast, the film has some disadvantages important as they are: sensitivity to light, the greater uncertainty in the high dose measurement and rather critical dependence of the development processes and measurement.

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