Exposure creep in computed radiography: a longitudinal study

Exposure creep is the gradual increase in x-ray exposures over time that results in increased radiation dose to the patient. It has been theorized as being a phenomenon that results from the wide-exposure latitude of computed radiography (CR) and direct/indirect digital radiography (DR). This project evaluates radiographic exposures over 43 months to determine if exposure creep exists and if measures can be applied to halt or reverse exposure creep trends.

Exposure indices were initially recorded over 29 months between August 2007 and December 2009 from the intensive and critical care unit (ICCU) and the emergency department (ED) departments where manual CR exposures were used. The data from this period were then assessed and the exposure indexes (EI) values from the radiographic images were compared to the radiology department criteria of EI values between 1400 to 1800 as being in the optimal exposure range. EI values below this were considered underexposed and over this as overexposed. An intervention was required to be used in ICCU and implemented in January 2010 to halt a noted trend of overexposure. The EI value for each chest x-ray (CXR) was recorded in the patients' ICCU records and was to be used by radiologic technologists/radiographers in determine exposure factors in subsequent CXR. After the intervention, EI values were recorded and evaluated for an additional 15 months between February 2010 and March 2011.

Between August 2007 and December 2009, 17,678 ICCU CXR images and 69,327 ED x-ray examinations were evaluated for over- and underexposure. A trend was noted in ICCU that showed a significant increase (P = .023) in EI values from the beginning to the end of the evaluation. No such trend was seen in the ED EI values (P = .120). After the intervention in ICCU, the overexposure trend was halted.

Exposure creep has been show to exist. It is surmised that this occurs where judgment to determine the correct radiographic exposure factors is needed when taking into account a large range of patient sizes. It has also been shown that providing radiologic technologists/radiographers with previous EI values for the same x-ray examination can halt a trend of exposure creep.