Читать книгу A Comprehensive Guide to Radiographic Sciences and Technology - Euclid Seeram - Страница 26

The overall objectives of radiation protection are to prevent deterministic effects and minimize the probability of stochastic effects. The current standards for radiation protection of patients in medicine are established by authoritative radiation protection organizations responsible for providing guidelines and recommendations on radiation protection. While some of these address radiation risks, others are devoted to radiation protection based on the radiation risks data. Three such organizations are the International Commission on Radiologic Protection (ICRP), the National Council on Radiation Protection and Measurements (NCRP), and the Food and Drug Administration (FDA), the latter two are in the United States.

Radiation protection criteria and standards are guided by two triads, namely radiation protection principles and radiation protection actions. While the former deals with the ICRP's principles of justification, optimization, and dose limitation, the latter addresses the triad of time, shielding, and distance. The principle of justification is intended for physicians ordering x‐ray examinations; it addresses the notion that there should be a net benefit associated with each and every exposure a patient receives. Optimization implies that radiation workers should work within the ALARA philosophy; that is, to obtain the best possible image with the lowest radiation dose and not compromise the image quality. Finally, the dose limits principle deals with the legal limits on the radiation dose received per year or accumulated over a working lifetime for persons who are occupationally exposed and for others as well, such as students in training and members of the public.

The triad of radiation protection actions include time, shielding, and distance. To be effective, it is necessary to keep the time of exposure to radiation as short as possible, since the relationship between time and exposure is proportional; that is, if the time of exposure doubles, the exposure doubles. Shielding ensures protection of patients and workers and members of the public through the use of lead shields and aprons for patients and workers, respectively. Furthermore, the walls of x‐ray rooms are also shielded using concrete or lead, for example, to prevent exposure of members of the public who are in a waiting room, waiting for patients having x‐rays. Finally, exposure is inversely proportional to the distance; that is, the further away individuals are from the source of the radiation, the less exposure they will receive.

The notion of dose limits is vital to radiation protection of occupationally exposed individuals such as technologists, for example, and non‐occupationally exposed individuals (members of the public). Essentially, these limits are established by organizations such as the ICRP, and national organizations, to minimize the risks of the stochastic effects of radiation. The ICRP recommended dose limit for occupational exposure, for example, is 20 mSv/year averaged over defined periods of five years.

The diagnostic reference level (DRL) is a concept used to address the limits of exposure for patients. DRLs are not equivalent to dose limit s for occupationally and non‐occupationally exposed individuals. The DRL has been defined by various radiation protection organizations. One such definition is that of the American College of Radiology (ACR) as “an investigation level to identify unusually high radiation dose or exposure levels for common diagnostic medical x‐ray procedures.” DRLs are tools that radiology departments can use to measure and assess radiation doses to patients for a defined set of procedures. If the doses delivered are consistently greater than established DRLs for that facility's country or region, then the department should be concerned about its radiation protection procedures, investigate why exposures are beyond the established DRLs, and take corrective action.