iaea human health series publications - SEDIM

authority with regard to radiation protection. Before construction of the mammography facility begins, approval forthe radiation shielding should be sought, as with any X ray facility.The medical physicist can assist in the calculation of barrier thicknesses and provide advice on documentationrequirements. Provision of adequate shielding for mammography is not normally difficult. Shielding is requiredonly to reduce exposure from scattered radiation, since the primary beam is limited to the area of the image receptorsupport. Typically, a total thickness of 24 mm of gypsum wallboard (fire code rated, two standard sheets) willprovide adequate shielding. The radiographer must have a transparent shield (nominally equivalent to 0.3 mm oflead) behind which he or she can stand while making an exposure. The exposure control must be designed so that itcannot be operated from outside this shielded area. The door to the room should be a solid core door; normally a firecode rated door will provide enough shielding.I.11. RADIATION PROTECTIVE ACCESSORIESIn modern screening mammography, there is negligible exposure to radiation sensitive sites other than thebreast. The main value of radiation protection apparel is psychological. If such apparel is to be supplied, it shouldonly be done at the request of the patient, and the apparel should not be kept on display in the examination room.The presence of the aprons and collars in the mammography room might suggest that their use is accepted practice,which is not the case.Both measurements and calculations show that the amount of radiation reaching the thyroid duringmammography is negligible. The amount of radiation reaching the ovaries is even less, due to the attenuation by thebreast support and that by the overlying tissue. Virtually all of the primary radiation is stopped by the breast and thebreast support; only an extremely low level of scatter reaches other parts of the body. The calculated dose to thethyroid for one four-view examination is less than 0.03 mGy. This is about 1% of the dose that would be receivedby the breast during the examination and is equal to the dose that would be received by the thyroid from 3 days ofnatural background radiation. In other words, this would be the equivalent of the client receiving 368 days ofnatural background radiation per year instead of the 365 days of background radiation that would be receivedwithout the examination. Natural variations in background radiation from locality to locality represent variationsmuch greater than this.I.12. INTERNET CONNECTIONAn Internet connection is generally required, but is in any case desirable, as modern systems can often bemonitored, faults can be diagnosed and software can be updated remotely.139