Xiang Li, Presenter: Research grant, General Electric Company

Ehsan Samei PhD, Abstract Co-Author: Advisory Board, Ion Beam Applications, SA Consultant, Siemens AG

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 Consultant, General Electric Company Research Consultant, Siemens AG

To estimate patient-specific radiation dose and cancer risk from pediatric chest CT examinations and to systematically evaluate factors affecting dose and risk, including patient size/age and scan parameters.

The study included 30 pediatric patients (0-16 years old). Full-body computer models were recently created from the patients’ clinical CT data. A validated Monte Carlo program was used to estimate organ dose received by each patient from eight chest scan protocols for a clinical CT scanner (LightSpeed VCT), representing clinically relevant combinations of bowtie filter, collimation, pitch, and tube potential. Organ dose was used to calculate effective dose, risks of cancer incidence for radiosensitive organs, and effective risk. The dose and risk estimates were correlated with body size. The effects of each scan parameter on dose and risk were independently studied.

Tube-current-normalized dose and risk estimates decreased exponentially with increasing average chest diameter. The medium bowtie filter was associated with the highest dose/risk. Compared with using a 20-mm collimation, using a 40-mm collimation resulted in slightly lower lung dose, higher large intestine dose, and slightly higher effective dose and effective risk. The ratio between pitch of 0.984 and pitch of 1.375 ranged between 1.37-1.38, 0.97-1.13, 1.28-1.32, and 1.27-1.33 for lung dose, large intestine dose, effective dose (male), and effective risk (male), respectively, lower than the theoretical value of 1.40 (1.375/0.984). The ratio between 120 kVp and 100 kVp ranged between 1.53-1.63, 1.54-1.69, 1.55-1.65, and 1.56-1.64 for lung dose, large intestine dose, effective dose (male), and effective risk (male), respectively, lower than the volume-weighted CTDI ratio of 1.70.

Radiation dose and cancer risk in pediatric chest CT are exponential functions of patient chest diameter. The effects of any scan parameter depend on patient size, which is not reflected by the difference in the volume-weighted CT dose index. The data provided in this study can serve as a basis library to determine effective dose and effective risk as functions of patient size and scan parameters for a variety of CT protocols.

Patient-specific dose and risk information may aid in decisions for image utilization, especially when multiple examinations are being considered. They can further guide the design of CT protocols.

Li, X, Samei, E, Segars, W, Sturgeon, G, Colsher, J, Frush, D, Patient Specific Radiation Dose and Cancer Risk in Pediatric Chest CT: A Systematic Evaluation of the Effects of Patient Size and Scan Parameters  .  Radiological Society of North America 2010 Scientific Assembly and Annual Meeting, November 28 - December 3, 2010 ,Chicago IL. http://archive.rsna.org/2010/9004642.html