Mireille Parent MSc, Abstract Co-Author: Nothing to Disclose

Chantale Lapierre MD, Abstract Co-Author: Nothing to Disclose

Sylvain Deschênes PhD, Presenter: Research Consultant, EOS imaging SA

Size-Specific Dose Estimate (SSDE) is a new metric proposed by American Association of Physicists in Medicine (AAPM) to better estimate irradiation from CT scan . Based on the patient dimension, SSDE offers a more accurate assessment of children dose who are not well represented by the phantom used for the computation of CTDIvol. We have calculated and compared SSDE and CTDIvol for chest and abdominopelvic CT performed in pediatric patients.

A retrospective study covering the last five years was conducted on 558 routine CT scans (chest: 461, abdominopelvic: 97). SSDE was calculated on examinations performed on a 64 array CT-scan in a children’s hospital. CTDIvol and phantom size were obtained from automatically generated dose reports whereas the patient’s dimensions were measured from axial images. SSDE conversion factors were taken from tables presented by AAPM Taskgroup 204.

Compared to SSDE, CTDIvol underestimates the dose received for all abdominopelvic CT and 91% of chest CT. For abdominopelvic examinations, the underestimation ranges between 1% and 130%, with 46% of cases being underestimated by more than 75%. For chest exams, underestimation reaches a peak at 157%, with 17% of cases being underestimated by more than 75%. Overestimation is encountered in 9% of the cases with a peak at 17%. We observed that SSDE and CTDIvol show better correlation when expressed with respect to weight rather than age.

Using CTDIvol commonly leads to false estimation and misinterpretation of the radiation dose received by patients undergoing a CT-scan. Conversely, SSDE is easy to calculate and offers a more truthful way to evaluate patient dose. Because of the weak correlation between patients’ age and dimensions, protocols built on the basis of age could lead to a less effective dose management. This emphasizes the idea that protocols would gain to be optimized as a function of weight since it better correlates with SSDE.

SSDE increases awareness of size effects on dose absorbed and provides a more accurate tool to assess risk for the patients.

Parent, M, Lapierre, C, Deschênes, S, Use of Size-specific Dose Estimate (SSDE) to Report CT-Scan Dose in a Children’s Hospital.  Radiological Society of North America 2012 Scientific Assembly and Annual Meeting, November 25 - November 30, 2012 ,Chicago IL. http://archive.rsna.org/2012/12025111.html