Table 6.

Limitations of existing epidemiologic studies of cancer risks in radiologists and radiologic technologists

Study characteristic	Limitations	Comment
Population size	Some are relatively small	Relatively small studies of radiologists: UK radiologists = 2700; U.S. radiologists = 6500 Limited statistical power to evaluate rare Cancers
Source of population	Not population-based	Radiologists identified from professional societies Technologists identified from professional societies or military
Nature of study populations	Some are heterogeneous	Some populations include radiologists and radiologic technologists (Danish, Chinese, Canadian) Risk data not reported separately for by specialty
Recency of follow-up, assessment of risk for workers performing newer procedures	Limited numbers of person-years of follow- up in recent decades ; little evaluation of cancer risks associated with newer radiologic procedures	Most studies ended follow-up before 1980s or 1990s No studies assessed risks associated with performing or assisting with fluoroscopically-guided or nuclear medicine procedures
Length of follow-up in relation to lifetime	Limited assessment of lifetime cancer risks	Atomic bomb survivor data point to the need for lifetime follow-up, since radiation- related cancers arise at same age as non- radiation-related cancers Study of UK radiologists demonstrated 40% increase in cancer mortality over lifetime, but small population size precluded precise cancer risk assessment
Quality and extent of dosimetric information	Limited dosimetry data	More than half of studies lacked dose data (UK radiologists, U.S. radiologists, U.S. Army technologists, & initial studies of U.S. radiologic technologists Some studies reporting dose data use indirect measures (Chinese) Studies reporting dose response (Japanese, Chinese, Danish, Canadian) describe only badge dose data All but one study describe only occupational exposure data