Ranish Deedar Ali Khawaja MD, Presenter: Nothing to Disclose

Sarabjeet Singh MD, Abstract Co-Author: Research Grant, Siemens AG Research Grant, Toshiba Corporation Research Grant, General Electric Company Research Grant, Koninklijke Philips NV

Atul Padole MD, Abstract Co-Author: Nothing to Disclose

Alexi Otrakji MD, Abstract Co-Author: Nothing to Disclose

Diego Alfonso Lira MD, Abstract Co-Author: Nothing to Disclose

Mannudeep K. S. Kalra MD, Abstract Co-Author: Nothing to Disclose

Da Zhang PhD, Abstract Co-Author: Nothing to Disclose

Bob Liu PhD, Abstract Co-Author: Nothing to Disclose

George Xu PhD, Abstract Co-Author: Nothing to Disclose

Andrew Primak PhD, Abstract Co-Author: Employee, Siemens AG

To determine the effect of patient centering technique on in-vitro organ dose measurements in a human cadaver scanned with routine abdomino-pelvic CT protocol. 

A human cadaver (88years, BMI 20 kg/m2) was scanned with a routine abdomino-pelvic CT protocol on a 128 slice-dual source MDCT (Definition Flash, Siemens). A total of 18 scans were performed using two scan protocols (a)120kV-200mAs fixed-mA (CTDIvol 14mGy) (b) 120kV-125mAs (7mGy) with automatic exposure control(AEC, CareDose 4D) at three different positions (a)gantry isocenter, (b)upward off-centering (c)downward off-centering. Scanning was repeated three times at each position. Six thimble (in liver, stomach, kidney, pancreas, colon, urinary bladder) & four MOSFET(on cornea, thyroid, testicle, breast) dosimeters were placed. Automatic dose measurements were also retrieved from dose-tracking software (Xposure, Bayer) for comparison. Statistical analysis was performed using SPSS v22. 

There was a significant difference between the trends of organ point doses with AEC and fixed-mA at all three positions (P <0.01). Degree of fluctuation of point dose between fixed-mA & AEC protocols was statistically significant across all organs at all table positions (P <0.001). With fixed-mA protocol, there was up to 5% decreased point dose with upward off-centering & up to 6% increased point dose with downward offcentering relative to gantry isocenter. With AEC protocol, there was up to 6% decreased & increased dose with upward & downward off-centering, respectively. With both protocols, there were statistical significant differences in point dose measurements at all positions derived from dosimeters &dose tracking software (mean difference for internal organs, 5-36% for fixed-mA & 7-48% for AEC protocols; P <0.001; mean difference for surface organs, >92% for both protocols; P <0.0001). For both protocols, the highest mean difference in point doses was found for stomach and lowest for colon.    

Measured absorbed organ doses in abdomino-pelvic CT vary significantly with patient centering in the gantry isocenter. Automatic dose tracking software did not capture the change in absorbed organ doses with patient off-centering.  

Patient off-centering directly affects in-vitro point dose measurements for body surface and internal organs. Urinary bladder, colon and liver point doses vary most significantly with off-centering. 

Khawaja, R, Singh, S, Padole, A, Otrakji, A, Lira, D, Kalra, M, Zhang, D, Liu, B, Xu, G, Primak, A, Effect of Patient Centering Technique on In-Vitro Human Organ Doses for Abdominal CT.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14004232.html