Hazards evaluation of neuroangiographic procedures.

The history of radiation protection in medicine has progressed through several distinct patterns prompted by observed or suspected biologic effects. The two preceding papers ( 1, 2) focus on what has in the past few years developed into an area of major concern. Radiographic and fluoroscopic imaging equipment dedicated to neuroangiography and progress in the tactile skill of neuroradiologists have resulted in ever-increasing radiation exposures of patients and personnel. These papers present useful data to a new, yet expanding base of information regarding exposure and dose accompanying neuroangiographic procedures. However, they both fall short of the mark of providing useful information on dose reduction. Within a year of the discovery of x-rays in November 1895 there were reports of radiation injury. These would be identified today as deterministic responses . A deterministic response to radiation is one that exhibits a severity that is dose dependent and follows a threshold-type dose response relationship (3). Classically, deterministic responses in radiation medicine are those of epilation, erythema, and other superficial responses . During the first 2 decades of this century, the principal hazards of exposure to medical radiation were electrocution and acute responses of superficial tissues. The literature is replete with individual reports of such injuries and also several excellent review articles (4-7). The focus during this period was on the patient, although some early radiation pioneers were injured or died as a consequence of their application of this new modality. By the middle 1920s, it was clear that x-ray operators were subject to severe harmful effects of their occupation. Some early pioneers had suggested restriction of radiation exposure, but it was not until 1925 that a measure of radiation intensity, the roentgen , was officially adopted. Immediately after this adoption , an occupa tional dose limit of 15 R/y was proposed by the newly formed International Commission on Ra diation Protection . In 1932, the US Advisory Committee on X-ray and Radium Protectionthe forerunner to the National Commission on Radiation Protection and Measurements-was formed and adopted similar dose limits. This stretch of radiation protection activity was directed principally toward reducing occupational radiation exposure. After World War II and the introduction of the atomic age, there was a flurry of activity resulting in an even more formal recognition of radi ation protection practices and in the development of the specific discipline of radiation biology. The focus shifted from deterministic to stochastic effects. Stochastic effects are those that exhibit no dose threshold and whose incidence is related to the dose rather than the severity of the response. Principal examples of stochastic effects are radiation-induced malignant disease and genetic mutations. During the 1950s and 1960s, radiobiologic investigations of the late effects of low-dose irradiation in animals were abundant. At the same time , human epidemiologic studies of a number of population groups, as shown in Table 1, flooded the literature , suggesting that even the smallest radiation exposure was accompanied by a finite risk of premature death . The focus of this activity among the responsible scientific bodies remained with the radiation worker, resulting in more precision in specifying occupational dose limits and a generalized lowering of those limits. Table 2 is a brief summary of this activity , shown graphically in Figure 1. Diagnostic radiologic practice over the last 10 years or so has become more aggressive, and now even therapeutic via angiointerven-