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

OBJECTIVE: To assess radiation dose for patients who received abdominal quantitative CT and to compare the midpoint dose [DL (0)] at the centre of a 1-cm scan length with the volume CT dose index (CTDIvol ). 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 DL (0).

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

RESULTS: 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 DL (0) was 2.97 ± 0.95 mGy (range, 1.18-5.77 mGy). As patient diameter increased, the DL (0) to CTDIvol ratio decreased, ranging from 1.24 to 0.25; the DL (0) to SSDE ratio also decreased, ranging from 0.61 to 0.38.

CONCLUSION: The dose to the patients from abdominal quantitative CT may be largely different from CTDIvol 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.