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

Ranish Deedar Ali Khawaja MD, Abstract Co-Author: Nothing to Disclose

Atul Padole MD, Presenter: Nothing to Disclose

Alexi Otrakji MD, Abstract Co-Author: 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

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

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

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

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

To measure point organ doses at different tube potential (kV) using fixed and automatic exposure control (AEC) techniques in a human cadaver experimental study. We also compared the measured organ doses to the estimated organ doses from a commercially available dose tracking software.

An 88 year-old male cadaver (height, 183cm & weight, 67kg, BMI 20 kg/m2) was acquired for this experiment from an accredited organization. Six thimble dosimeters were surgically placed in following locations: (i) stomach, (ii) urinary bladder (iii) ascending colon, (iv) liver, (v) pancreas, and (vi) left kidney. The cadaver was iso-centered in the gantry and scanned on a 128 slice dual source MDCT (Siemens Definition Flash CT) at 8 different settings – 4 with AEC (at constant CTDIvol 2.5mGy) & 4 with fixed mA (at constant CTDIvol 4mGy). Scans were performed at 80, 100, 120 and 140 kV with mA values changed to achieve the aforementioned CTDIvol for each kV. Scans were repeated 3times for each of the 8 scanning protocols. All image series were exported to a dose tracking software (Xposure, Bayer) to obtain absorbed organ doses for comparison. Image noise was measured in the liver and pelvic fat. ANOVA and Pearson correlation coefficients were used for analysis.

At constant CTDIvol, there was a significant fluctuation in measured organ doses with changes in the applied kV with lower kV associated with lower point doses. There were significant differences in measured and estimated (from software) organ doses at constant CTDIvol at different kV settings (p <0.005). At constant CTDIvol, mean point dose measurements increased with kV ranging from 10-34% for fixed mA & 20-30% for AEC protocol. Urinary bladder had the highest point organ dose at all tube potentials compared to other organs while kidney point dose was the lowest (p <0.001). Compared to measured point dose measurements, there was 8-33% overestimation (stomach, liver, intestine) & 11-19% underestimation by the dose tracking software (kidney, bladder, colon).

At constant CTDIvol, both measured and calculated (with software) organ doses fluctuate substantially with changing kV, with lower kV settings associated with lower dose in both fixed and modulated mA.

CT at lower kV settings is associated with lower organ doses even at constant CTDIvol.

Lira, D, Khawaja, R, Padole, A, Otrakji, A, Singh, S, Kalra, M, Liu, B, Zhang, D, Xu, G, Effect of KV on CT Radiation Dose: Internal Organ Dosimetry in a Human Cadaver.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14017933.html