Xiang Li, Presenter: Research grant, General Electric Company

Ehsan Samei PhD, Abstract Co-Author: Advisory Board, Ion Beam Applications, SA Advisory Board, onTargetJobs

William Paul Segars PhD, Abstract Co-Author: Nothing to Disclose

Gregory M Sturgeon MS, Abstract Co-Author: Nothing to Disclose

James G. Colsher PhD, Abstract Co-Author: Employee, General Electric Company

Donald P. Frush MD, Abstract Co-Author: Research funded, General Electric Company

Current methods for organ and effective dose (ED) estimations in pediatric MDCT are very limited. Our purpose was to use actual pediatric (patient-specific) MDCT data to determine a more accurate method for these dose estimations.

The IRB waived informed consent for this study. The study consisted of 6 pediatric patients, aged 3-11 years old, weighting 21-43 kg, who underwent MDCT (VCT, GE) examinations. The scan protocol investigated was the standard size-based chest scan protocol: 120 kVp, 80 or 95 mA, 0.4-second gantry period, pitch of 1.375, and medium bowtie filter. An NURBS (nonuniform rational B-spline) based computer model (technique similar to that used in Pixar animation) of each patient was created using the patient’s actual CT data (ref: abstract ID # 6016700), with each organ individually mapped. Organs outside the scan coverage were added according to patient age to match the ICRP 89 reference standards. The models were voxelized at 2-mm isotropic resolution for input into a Monte Carlo code. The Monte Carlo code was previously developed based on PENELOPE (Universitat de Barcelona) and was used to model the exact imaging geometry and protocol. The code was benchmarked against experimental measurements (dose error < 5.4%).

The 6 patients had a chest MDCT ED of 1.4-2.0 mSv. For a given size group (21-24 kg), ED was variable (5.2%), but was generally smaller in magnitude than the variation in organ dose (4.4%-31.6%). Formulae that relate total mAs per scan (instead of the conventional mAs per slice) and scan length were derived which allowed ED and directly exposed large organ doses to be reliably determined (heart: 3.68 mGy-4.40 mGy, lung: 3.62-4.08 mGy, bone marrow: 0.56-0.72 mGy). Dose estimation, however, was less deterministic for small organs in the beam and for partially or indirectly exposed organs.

This investigation provides a more accurate ED determination method for a set of chest MDCT parameters and patient sizes than existing models or the DLP method, and provides unique and previously unavailable methods for organ dose estimations that may help in assessing risk including use in IRB reviews of chest MDCT in children.

Unique organ dose and more accurate ED calculations enable more accurate radiation risk estimations in children undergoing chest MDCT.

Li, X, Samei, E, Segars, W, Sturgeon, G, Colsher, J, Frush, D, Pediatric Chest MDCT: Unique Method for Patient-specific Organ and Effective Dose Estimations.  Radiological Society of North America 2008 Scientific Assembly and Annual Meeting, February 18 - February 20, 2008 ,Chicago IL. http://archive.rsna.org/2008/6015246.html