Clinical Radioprotection

        Another general aspect to evaluate is the action of radiations in regard to time. There are two type of effects, acute and chronic. One form of the first one occurs when large activities of radiation deliver their energy to the whole body in a very short lapse of time, producing the Acute Radiation Syndrome. It will depend on the amount of absorbed radiation, the clinical presentation. One is the hematopoietic and occurs with doses of 1 to 10 Gy and presents within a week of receiving the radiation. The gastrointestinal form for doses between 10 and 50 Gy and starts after several days and the neurological form with doses greater than 50 Gy and begins in hours.

        In relation with chronic effects, there are a couple of examples interesting to discuss. One is the case of gonads, testis and ovary, which might be affected by sterility. The latency period is of 2 months and 1 month, respectively and the threshold dose over which it could occur is of 0.2 Gy to 0.5 Gy, and doses that produce severe effects in the range of 3 Gy . In these cases, the consequences would be aspermia of the specific cells in the testis and oocyte interphase death in the ovary. The other one we may look at, is what might happen at the level of crystalline cataracts which are generated with a period of latency of over a year, having a 0.2 Gy dose threshold and maximum effective dose of 5 Gy. The specific cause is failure of maturation with loss of transparency.

        To prevent all possible harmful consequences of ionizing radiations, it is  important to handle radioactive sources with care and in the safest possible way. The classical 3 factors that protect us from the effects of radiation  are: Time, Distance and Shielding. It is obvious that the longer the period of time in contact with a radioactive source, the more exposure and eventual effects. For example, it is a wise decision to talk and examine the patient before it is administered the radiotracer or therapy.  The action of radioactivity increases exponentially,  the closer to the source. The amount received may increase by a factor of 4 if the distance decreases by a factor of 2. In other words, the radiation will augment or diminish inversely with the square of distance. Most frequent radiations employed in nuclear medicine can be made safer if appropiate shielding accessories, such as lead aprons and glassess are worn. They help us keep our exposure as low as possible. This is particularly important in treament procedures when 131-I, 90-Y or 177-Lu  is utilized.

The laboratory

        This a room that needs to be of appropiate size with space to store the different radioactive tracers, built with concrete walls or shielded with at least 1 mm lead thickness, overlapped 2 mm over each other, so not to leave any areas for leaking. Professionals should be aware of the specific requirements and legislation in this regard in each country. It is important to take care of all sort of details, before the construction, and tailored to the specific needs. A license must be obtained and issued by the health authority. A further shielded space 1 x 2 m, inside the hot lab  it is important to keep the larger radiation activities of radionuclides. It must include an area for equipment (Geiger Muller detector, Dose Calibrator), refrigerator for the different molecules to be labeled and area for radioprotection accessories. Likewise, sink and the area to wash different materials. Special mention for the shielded cell for labelling and preparing the different radiotracers and pharmaceuticals. When using 131-Iodine it is important to run an air extractor provided with carbon activated hood to trap any iodine sublimation. The furniture, walls and floor must be covered with plastic and smooth surfaces, avoiding rugosity and porosity and easy to clean. It is important to keep at hand written protocols of the different procedures carried out in the hot lab, including wasting and contamination handling of spills. Likewise, contamination surveillance has to be done at the end of the day, keeping records of every thing that has been done. At the start and whenever an architectural modification takes place, the license should be obtained or renewed. Same if the laboratory is decommissioned.

            When manipulating radiotracers it is important to prevent incidents that might affect personnel and patients (3).

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