Clinical Radioprotection

b) Thermoluminescent Dosimeter.

            It is called thermoluminescence (TL) the light emission of certain substances after being exposed to ionizing radiation. Ionizing radiation passing through certain materials deliver their energy producing excitation phenomena. The peculiarity of materials used in thermoluminescence dosimetry, also known as TLD, is that the de-excitation with subsequent emission of light does not occur immediately, but needs the heating for it to occur. The intensity of light emitted emitted by a photomultiplier, is directly related to the radiation dose received by the material. The most suitable materials are synthetic, TLD (LiF, CaF2, CaSO4, Al2O3, etc.) with small amounts of impurities (LiF: Ti, Mg), (LiF: Mg, Cu, P), (CaF2: Mn), (Al2O3: C). Dosimeters  house these elements  in a small portable case.  Thermoluminescence dosimeters are more accurate than film. This, together with the fact they can be erased and reused repeatedly, makes its utilization widespread. As a disvantage, the information cannot be archived in the dosimetric history as with photographic film .

c) Ionization  Dosimeter.

            When ionizing radiation passes through a gas, it causes in a portion of its atoms to release positive ions and electrons. The gas that previously acted as an electrical insulator, becomes partly conducting. Measuring the generated electric current it can be deduced, under certain conditions, the intensity of radiation passing through it.

Operational dosimeters

            They are smalldigital direct reading dosimeters, using a gas ionization detector or silicon detector. Upon reaching a preset absorbed dose, they emit an acoustic signal. Delivering at any moment the value of the cumulative dose on a digital readout system, which allows instant reading of doses and dose rates for deep and superficial dose.

Monitors of exposure or dose rate

            The radiological surveillance of work areas, in areas with a risk of operating in fields ionizing radiation is performed by radiation monitors that measure the exposure, dose absorbed or the respective rates in particular areas. These instruments are worn as body an ionization chamber detector and a Geiger counter Figure 4 and are fitted with windows thin wall, hidden by movable absorbing screens in order to measure, although the effect set of beta and gamma radiation (open window) or only the gamma component (window closed). They have the ability to modify the appropriate measurement range of the radiation field of interest. To verify the correct functioning of these tools each team is provided with a verification source beta or gamma irradiation should produce the sample determined by placing projected at a point detector. Also, on all monitors a system of checks battery state, in which the needle of the instrument must be located in an area identified a stroke or shaded area, on the cover of the measuring instrument.

            The portable monitor ionization chamber equipped with a sensitive volume tend to have the order 0.5 liter and used as filling gas air at atmospheric pressure. The measuring range is usually 1 to 1000 mR / h. The Geiger counter equipped systems are much more sensitive than ionization chamber, and usually have a switch at the end of a probe connected to a power detector to several meters in length, or a telescopic system facilitating measures in areas of high activity or in confined spaces. The Geiger counter, which offers the important advantage of achieving detection performance close to 100% for beta and alpha particles, is nonetheless of efficiency of about 1% for radiation gamma. Sometimes the source of ionizing radiation is fixed and well located, but its condition can vary and, at all times, you must know the level of radiation that exists around you or in a remote area. Ionization chambers can be placed at appropriate points and using cables, these cameras send their instantaneous measurements to instruments located in the control room. The operator can know the level and of radiation in the points where the detectors are. These monitors often have an alarm which produces an audible signal or light when the radiation level exceeds a predetermined value.

Member of the Public Considerations

        Areas surrounding radiation laboratories must generate always low doses for the public. The ICRP suggests that a maximun of 1 mSv effective dose annually, corresponding to the summation of all controlable radioactive sources,  should not be exceeded. The effective dose is  related to the risk of a radiation-induced cancer or a severe hereditary effect. 1) the absorbed doses during the lifetime of an individual; 2) the absorbed doses due  external sources; 3) the relative effectiveness of  radiation in inducing cancers or severe hereditary effects; 4) the susceptibility  to develop a radiation-related cancer or severe hereditary effect; 5) considerations of  fatal and non-fatal effects; 6) the average years of life lost from a fatal health effect.

Relatives and Accompaniyng Persons

        This is important in patients receiving therapy, in particular with radioiodine. Usually if the dose is over 111 MBq (30 mCi), patients are hospitalized till the exposure rate at 1 m is below 25 uSv/h  (2.5 mrem/h). Either after hospitalization or receiving the radiodine in an outpatient basis, patients must go directly home by car avoiding any means of public transportation. At home relatives are advised to stay at 1 m or more during 1 week in the case of carcinoma therapy and 2 weeks in hyperthyroidism cases, starting count day receiving the 131-I. Likewise, the patient has to sleep alone. As an exception to these limits, the isolation period has to be doubled to 1 month for small children and pregnant women in the family.

References:

1     González P. Protección contra radiaciones ionizantes en hospitales. Rev Med Chile. 1988; 116: 174‑179.

2    International Commission on Radiological Protection (ICRP). 1990 Recommendations of the International Commission on Radiological Protection. Oxford: Pergamon Press; ICRP Publication 60, Ann. ICRP 21(1-3); 1991.

3      Martin CJ. A survey of incidents in radiology and nuclear medicine in the West of Scotland. Br J Radiol. 2005 Oct;78(934):913-21.
 

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