X-ray examination dose surveys: how accurate are my results?

OBJECTIVES

To determine the variabilities of dose-area-products (DAP) of frequent X-ray examinations collected for comparison with diagnostic reference levels (DRLs).

METHODS

DAP values of chest, abdomen, and lumbar spine examinations obtained on devices from two manufacturers were collected in three centers over 1 to 2 years. The variability of the average DAP results defined as the 95% confidence interval in percentage of their median value was calculated for increasing sample sizes, each examination and center. We computed the sample sizes yielding variabilities lower or equal to 25% and 10%. The effect of narrowing patient selection based on body weight was also investigated (ranges of 67-73 Kg, or 60-80 Kg).

RESULTS

DAP variabilities ranged from 75 to 170% of the median value when collecting small samples (10 to 20 DAP). To reduce this variability, larger samples are needed, collected over up to 2 years, regardless of the examination and center. A variability ≤ 10% could only be reached for chest X-rays, requiring up to 800 data. For the abdomen and lumbar spine, the lowest achievable variability was 25%, regardless of the body weight selection, requiring up to 400 data.

CONCLUSION

Variabilities in DAP collected through small samples of ten data as recommended by authorities are very high, but can be reduced down to 25% (abdomen and lumbar spine) or even 10% (chest) through a substantial increase in sample sizes. Our findings could assist radiologists and regulatory authorities in estimating the reliability of the data obtained when performing X-ray dose surveys.

KEY POINTS

• Low but reasonable variabilities cannot be reached with samples sized as recommended by regulatory authorities. Higher numbers of DAP values are required to reduce the variability. • Variabilities of 10% for the chest and 25% for abdomen and lumbar spine examinations are achievable, provided large samples of data are collected over 1 year. • Our results could help radiologists and authorities interpret X-rays dose surveys.