Size Specific Dose Estimate in Abdominal Computed Tomography by AAPM TG Report-204 and AAPM TG Report-220

Abstract

Purpose: The AAPM Task Group (TG) reports 204 and 220 presented methods for evaluation of patient dose by announcing the SSDE. The TG reports provide the Size Specific Conversion factors that can be multiplied to CTDIvol to calculate the patient dose in terms of SSDE constructed from Deff (AAPM TG-204) and Dw (AAPM TG-220). Our study presents a comparison of the two TG reports on SSDE for the routine Abdominal Computed Tomography. Materials and Methods: The scan lengths of abdomen were measured from computed tomography (CT) topographic images and cross-section at the mid-slice of the abdomen were measured from tomographic images of 61 adults who had undergone abdominal CT using the GE Advance Workstation (AWS) software. The Deff and Dw was computed according to TG- 204 and TG-220 reports, respectively. Further, we performed the correlation analysis between Deff and BMI, Dw and BMI and SSDE and BMI for both the TG- reports. The Student’s paired t-test was performed to compare the two of SSDE calculation methods. Results: The results confirm that the mean value of SSDE is 13.04 (𝑚𝐺𝑦) and 13.60 (𝑚𝐺𝑦) for AAPM TG-220 and AAPM TG-204, respectively. And a good positive correlation was observed between Deff and BMI, Dw and BMI with r = 0.67 and r = 0.68 respectively. Also, the weak correlation was observed between SSDE and BMI for both the TG - reports. The Student’s paired t-test shows that the two means of SSDE calculation methods are significantly different (𝑝< 0.01) in abdominal computed tomography. Conclusion: We confirm the AAPM TG reports 204/220 using clinical data for SSDE calculation that the mean SSDE values computed from Deff and Dw in abdomenal computed tomography are significantly different and we conclude that the SSDE calculated by Dw method gives a more accurate evaluation of SSDE for the patients undergoing abdominal computed tomography scan then the SSDE calculated by Deff method.