Body-Size Estimates Critical in Determining Effective Dose

Diagnostic reference levels (DRLs) help reduce patient radiation dose used in most frequently performed CT examinations without degradation in image quality, according to a study published in the American Journal of Roentgenology. Researchers from Canada sought to establish provincial DRLs and to determine whether this process may help reduce the patient radiation dose from head, chest, low-dose chest, abdomen and pelvis, and chest, abdomen, and pelvis CT examinations, which are the most frequently performed CT examinations. The researchers used a sample for each protocol that included 15 patients of average body weight of 70 kg, and the initial survey included data from 1,185 patients. An additional 180 patients were surveyed after protocol optimization. A sample of abdominal and chest examinations were randomized and blinded for review by experienced radiologists who graded diagnostic image quality. Provincial DRLs were calculated as the 75th percentile of patient dose distributions. For hospitals with doses exceeding the DRLs, dose reduction was recommended, followed by another survey. The results showed the differences between the mean values of the dose distributions from each scanner were statistically significant (p < 0.05) for all examinations. The variation was greatest for low-dose chest CT, with a greater than five-fold difference in the mean dose values noted between scanners. A very weak correlation was found between dose and scanner age or the number of detector rows. Analysis of image quality revealed no statistically significant differences in any scoring categories, with the exception of the noise category in abdominal imaging. Implementation of the DRLs allowed a reduction in patient dose of up to 41 percent as a result of a protocol change.  Study                                           Dose reduction following modificationAbdomen and pelvis CT               33.6% - 40.4%Chest, abdomen, and pelvis CT   30.9% - 40%Head CT                                         2.2% - 22% The researchers concluded that establishing provincial DRLs allowed an effective reduction in patient dose without resulting in degradation of image quality.