Application of draft European Commission reference levels to a regional CT dose survey.

Abstract

A survey of CT doses in Northern Ireland in the period between October 1995 and March 1997 was carried out. The survey included all but one of the 10 scanners in use at the time, and, additionally, two others that were replacement machines. The method used was to study standard protocols and calculate doses to the NRPB mathematical phantom, so that a direct comparison could be made with other surveys carried out in a similar fashion elsewhere. The survey addressed the patient radiation dose but not image quality or clinical outcomes. It is estimated that in Northern Ireland the contribution to collective dose to the population from CT is about 40% of that from all medical X-rays. The proposed European Commission reference quantities, weighted CT dose index and dose-length product were computed and their potential use evaluated. A full study of mean values of effective dose per examination revealed the average dose per examination was not significantly different from that found in the 1989 UK survey, although several procedures gave rise to doses that were high enough to be investigated with a view to justification or reduction. One of the scanners was found to give consistently high doses. It is likely that a revision of the mAs values used on this scanner will produce a significant reduction in patient doses without compromising image quality. When compared with the draft EC reference levels, fewer procedures were found to have excessively high dose values. The proposed EC reference levels would therefore be useful for continual monitoring of CT dose status, but do not appear to provide as comprehensive an assessment of patient exposure as that given by consideration of effective doses.

Report of a workshop: quantitative computed tomography scanning in longitudinal studies of emphysema

“…CT examinations in 1994 in Germany made up 4.2% of the total number of radiological examinations but contributed 37.8% of the entire effective radiation dose to the German population [9]. Similar results have been reported in the UK, where it is estimated that CT makes up 4% of the total radiological examinations and contributes 40% of the effective radiation dose to the population [43,44].…”

“…The phantom results should verify that the dose used for the study is adequate to provide reliable quantitative measures of emphysema while keeping the radiation dose as low as possible. If only measures of lung density are required recent research suggests that 140 kVp and 20 mas may be adequate for accurate results with an expected effective radiation dose to the subject of 0.7 mSv [44].…”

Organ doses for reference adult male and female undergoing computed tomography estimated by Monte Carlo simulations

“…However, this is not surprising because the significant variations in the CTDI w among different clinical sites have been reported with the same CT scanner model and scanning protocols. [46][47][48] If the organ doses are scaled by the actual measurement of the CTDI w under a CT scanner of interest, it will substantially improve the accuracy of the resulting organ doses. However, the measurement is not feasible in most cases of the organ dose reconstruction for patients examined in the past ͑as in radiation epidemiology studies͒.…”

Radiation dose reduction without degrading image quality during computed tomography examinations: Dosimetry and quality control study

“…8 Effective dose calculation is the best available predictor of the stochastic risk of a given radiological examination as it estimates or calculates the dose of organs. 9 Study by Wade JP et al 10 concluded that, the effective dose for the head scan is considerably less than that for the trunk scans, even though the CTDI values for head scan are much higher. This is because fewer of the radiosensitive organs are irradiated.…”