[en] Objective: To compare the difference between volume computed tomography dose index (CTDI_vol) and size-specific dose estimates (SSDE) in evaluating the radiation dose of abdominal CT scan. Methods: Abdominal CT scan were performed on 180 patients with a Philips 256-slices spiral CT. The anterior-posterior dimension (AP) and lateral dimension (LAT) of each patients were measured at the level of left renal vein, and the effective diameter (ED) and SSDE were calculated with recorded CTDI_vol Patients were categorized into 3 groups depending on body mass index(BMI): group A, BMI < 20.0 kg/m²; group B, 20.0-24.9 kg/m²; group C, BMI > 24.9 kg/m². The differences between CTDI_vol and SSDE of 180 patients and three different BMI groups were compared respectively. Results: There was a significant difference between CTDI_vol and SSDE of the 180 patients (t = -13.354, P < 0.01), CTDI_vol and SSDE were (9.91 ± 2.91) and (14.01 ± 2.82) mGy, respectively. For group A, CTDI_vol and SSDE were (7.96 ± 1.83) and (12.83 ± 2.52) mGy, respectively (t = -8.417, P < 0.01). Group B, CTDI_vol and SSDE were (9.28 ± 1.76) and (13.62 ± 2.18) mGy, respectively (t = -15.051, P < 0.01). Group C, CTDI_vol and SSDE were (12.19 ± 3.65) and (15.39 ± 3.47) mGy, respectively (t = -4.535, P < 0.01). In addition, the mean percentage values of difference between CTDI_vol and SSDE for the three groups were 62.83%, 47.80%, 28.40%, respectively, which meant CTDI_vol underestimated the radiation dose compared to SSDE. With the BMI increasing, the values of difference between CTDI_vol and SSDE decreased. Conclusions: SSDE can be used to estimate the radiation dose of abdominal CT scan for a given size person. (authors)