Assessment of radiation dose from abdominal quantitative CT with short scan length

To assess radiation dose for patients who received abdominal quantitative CT and to compare the midpoint dose [D_L(0)] at the centre of a 1-cm scan length with the volume CT dose index (CTDI_vol). Although the size-specific dose estimate (SSDE) proposed in The American Association of Physicists in Medicine Report No. 204 is not applicable for short-length scans, commercial dose-monitoring software, such as Radimetrics^™ Enterprise Platform (Bayer HealthCare, Whippany, NJ), reports SSDE for all scans. SSDE was herein compared with D_L(0).

Data were analyzed from 398 abdominal quantitative CT examinations in 165 males and 233 females. The CTDI_vol was 4.66 mGy, and the scan length was 1 cm for all examinations. Radimetrics was used to extract patient diameter and SSDE. D_L(0) was assessed using a previously reported method that takes into account both patient size and scan length.

The mean patient diameter was 28.5 ± 6.3 cm (range, 16.5-46.6 cm); the mean SSDE was 6.22 ± 1.36 mGy (range, 3.12-9.42 mGy); and the mean D_L(0) was 2.97 ± 0.95 mGy (range, 1.18-5.77 mGy). As patient diameter increased, the D_L(0) to CTDI_vol ratio decreased, ranging from 1.24 to 0.25; the D_L(0) to SSDE ratio also decreased, ranging from 0.61 to 0.38.

The dose to the patients from abdominal quantitative CT may be largely different from CTDI_vol and SSDE. This study demonstrates the necessity of taking into account not only patient size but also scan length for evaluating the dose from short-length scans. Advances in knowledge: In CT examinations with 1-cm scan length, dose evaluation needs to take into account both patient size and scan length. An omission of either factor can result in an erroneous result.