Purpose: To estimate conversion factors for calculating effective dose (E) and organ dose taking tube current modulation (TCM) and patient size into account in adult thorax and abdomen CT examinations. Method: 99 consecutive adult patients were included in this study. All examinations were performed with TCM (CareDose 4D. Siemens Definition Flash) at 120 kVp and 110 (thorax) and 200 (abdomen) reference mAs. E and organ dose were estimated with PCXMC 2.0 (STUK. Helsinki. Finland). using an extension of the software from a planar geometry to spiral acquisitions of aCT scanner. This software accounts for patient size by rescaling the anthropomorphic phantom to actual patient weights and heights. E and organ doses were normalized to the CTDi_vol as reported in the patient's report. These conversion factors (d_E and d_organ were studied as a function of different patient metrics: lateral and anterior-posterior (AP) diameter. sum of the lateral and AP diameter, area of a cross section image and effective diameter. Results:. No trend was found for any of the metrics neither forE nor for the organs investigated (lungs. breasts. stomach and liver). Average value ± 2 standard deviation were calculated. For a thorax examination, the average d_E was 0.57 ± 0.14 mSv/mGy. d_lungs was 1.26 ± 0.28 mGy/mGy and d_breasts was 1.29 ± 0.40 mGy/mGy. For an abdomen scan dE was 0.82 ± 0.18. mSv/mGy. d,tomooh was 1.42 ± 0.26 mGy/mGy. d_liver was 1.42 ± 0.30 mGy/mGy. Conclusion:. For the scanner studied, average conversion factors, which account for TCM and patient size, were proposed. This is a first step towards patient-specific dosimetry.

Date Published: 6 March 2013
PDF: 8 pages
Proc. SPIE 8668, Medical Imaging 2013: Physics of Medical Imaging, 866842 (6 March 2013); doi: 10.1117/12.2007880

Published in SPIE Proceedings Vol. 8668:
Medical Imaging 2013: Physics of Medical Imaging
Robert M. Nishikawa; Bruce R. Whiting; Christoph Hoeschen, Editor(s)