Xochitl Lopez-Rendon MSc, Presenter: Nothing to Disclose

Guozhi Zhang, Abstract Co-Author: Nothing to Disclose

Raymond H. Oyen MD, PhD, Abstract Co-Author: Nothing to Disclose

Hilde Bosmans PhD, Abstract Co-Author: Co-founder, Qaelum NV Research Grant, Siemens AG

Federica Zanca PhD, Abstract Co-Author: Nothing to Disclose

To estimate organ doses from longitudinally modulated chest CT scans with CT-Expo dosimetry software and full Monte Carlo (MC) simulations for normal size patients.

Data from 9 patients (4 female, 5 male) with normal BMI (20.3- 24.4), who underwent a chest scan on a Siemens Definition Flash scanner were collected. Examinations were performed with longitudinal TCM, 120 kV and 110 reference mAs. Patients organ doses (lungs for both gender and breasts only for female) were calculated using the new CT-Expo v. 2.2, which includes a dose correction for exams performed with tube current modulation. Specifically it uses two unique mAs profiles, one for male and one for female, which are modified based on the specific scan range by a set of correction factors for each z-position every cm. Dose to the same organs were also calculated with MC simulation (EGSnrc) for the ICRP phantoms, but this time using the patient specific tube current modulation profiles. The longitudinal TCM information from each patient was extracted from the images using an in-house tool. Percentage error between the dose calculated with the full MC simulation and the commercial software was assessed with respect to the MC simulations.

For all the patients, doses estimated with the full MC simulation were higher than with CT-Expo. For female patients, the percentage error for breasts ranged from 3.9 to 12.4%, while for the lungs from 10.8 to 21.2%. The percentage error for dose to the lungs for male patients ranged from 10.9 to 13.3%.

All included patients were similar in BMI to the stylized CT-Expo phantoms and to the ICRP anthropomorphic phantoms used for MC simulations. Observed organ dose differences are due to the stylized phantoms and the two single TCM profiles used in CT-Expo. TCM profile can vary considerably even across normal size patients due to different body habitus.

To have accurate patient specific organs doses, even for normal patient sizes, MC simulations have to be preferred.

Lopez-Rendon, X, Zhang, G, Oyen, R, Bosmans, H, Zanca, F, Organ Doses from Longitudinally Modulated Chest CT Scans in Commercial Software and Monte Carlo Simulations.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14017712.html