Xochitl Lopez-Rendon MSc, Presenter: Nothing to Disclose

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

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

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

To evaluate patient-specific effective dose (E) estimations obtained with CT-Expo and PCXMC, for thorax and abdomen CT exams performed with TCM.

99 consecutive adult patients (47 female, 52 male) underwent thorax/abdomen scans performed with TCM (Siemens Definition Flash) at 120 kVp, 110(thorax) and 200(abdomen) reference mAs. Longitudinal TCM information and CTDIvol (based on patient average effective mAs) were registered. To compute E (ICRP 103 guidelines), CT-Expo (v.2.0) and PCXMC (v.2.0) calculators were used. CT-Expo permits gender-specific E estimations, for a normal size adult phantom, uses patient average effective mAs and built-in beam qualities. Instead, PCXMC 2.0 allows estimation of E for a hermaphrodite phantom resizable to patients’ dimensions and can be adjusted to use patient’s modulated mAs; equivalent filtration has to be specified. Wilcoxon test was applied to asses estimated E for statistical significant difference.

CT-Expo predicts significantly higher values (p<0.001) for thorax scans in female patients (CT-Expo median 4.9±1.5 mSv, PCXMC 3.4±0.9 mSv), due to the use of average mAs. TCM indeed decreases the mAs at the lungs and breast. For thorax male, no significant difference was found (p=0.8, CT-Expo median 4.2±1.2 mSv and PCXMC 4.3±1.0 mSv) as the TCM dose reduction is partially offset by the use in PCXMC of a hermaphrodite phantom that accounts for breast dose regardless of gender. For abdomen CT, a significant difference (p<0.001) was found for both female and male (CT-Expo median 8.0 ± 4.5 mSv and PCXMC 7.5 ± 2.7 mSv, CT-Expo median 7.2 ± 2.4 mSv and PCXMC 8.2 ± 2.4 mSv, respectively). TCM profiles for male exhibited higher mAs at the stomach and liver than for female, which explain PCXMC higher E than CT-EXPO.

Neither CT-Expo nor PCXMC provides a realistic estimation of patient-specific E. CT-Expo is not meant for estimating patient specific dose, as it does not account for patient size and TCM. PCXMC accounts for patient size and TCM but not for beam shaping filters; patient size rescaling is based on organ rescaling; no fat is added. Moreover, E is not gender dependent but an average of male and female doses.

Accurate dose estimation in CT is needed, but current software is outdated for state-of-the-art CT. New software tools should be tuned towards patient-specific organ doses, TCM and shaped filters.

Lopez-Rendon, X, Bosmans, H, Oyen, R, Zanca, F, Towards Patient-specific Dose Estimation for Thorax and Abdomen CT Exams Performed with Tube Current Modulation (TCM): What Can Be Obtained With Existing Dose Calculation Tools.  Radiological Society of North America 2012 Scientific Assembly and Annual Meeting, November 25 - November 30, 2012 ,Chicago IL. http://archive.rsna.org/2012/12043893.html