Choonsik Lee PhD, Presenter: Nothing to Disclose

Randell L. Kruger PhD, Abstract Co-Author: Nothing to Disclose

Philip F. Judy PhD, Abstract Co-Author: Nothing to Disclose

Wesley E. Bolch PhD, Abstract Co-Author: Nothing to Disclose

Dianna D. Cody PhD, Abstract Co-Author: In-kind support, General Electric Company

Michael James Flynn PhD, Abstract Co-Author: Nothing to Disclose

We calculated doses to major organs associated with CT screening examinations for 23,773 CT scans, a subset of the total cohort of the National Lung Screening Trial (NLST), using a library of computational human phantoms coupled with Monte Carlo radiation transport technique.

First, we collected scan parameters (patient ID, age, gender, height, weight, scanner manufacturer, model, scan length, kVp, and mAs) from 23,773 CT scans. Second, organ dose conversion coefficients (organ dose normalized to CTDIvol of a reference CT scanner) was calculated using Monte Carlo code, MCNPX2.7, where experimentally-validated CT scanner simulation was coupled with 193 adult hybrid computational phantoms representing the height and weight of the current U.S. population. Finally, dose to selected organs (lung, heart, and thyroid) were calculated by using the organ dose library and the abstracted scan parameters. The other set of organ doses was also calculated for comparison using organ dose conversion coefficients based on a single adult male phantom with reference body size.

We established a comprehensive organ dose library for 193 adult phantoms: six dimensional dose matrix, D (31 organs, 190 slices max, 7 height bins, 19 weight bins, 2 genders, and 6 x-ray spectra). Patient size-specific organ doses were calculated for 23,773 CT scans using the dose library coupled with abstracted technical parameters. Mean doses to lung, heart, and thyroid were 4.5 (SD=1.6), 4.5 (SD=1.6), and 3.7 (SD=2.0) mGy, respectively, while mean CTDIvol was 3.6 mGy (SD=1.2). Organ doses based on the reference size phantom under- or over-estimated the values of thin and obese patients, respectively, up to 60%.

We calculated individualized doses to major organs for 23,773 CT scans involved in the NLST by using size-dependent computational phantoms coupled with Monte Carlo calculations. The organ dose conversion coefficients and batch calculation technique developed in this study can be also used for other studies including patient dose monitoring, epidemiological studies of cancer risk, and the analysis of CT dose trend.

The results from the study provide the individualized organ dose estimations for NLST patient cohort. The dosimetry method used in this study will be useful for calculation patient size-specific organ dose in other studies without performing intensive Monte Carlo simulation.

Lee, C, Kruger, R, Judy, P, Bolch, W, Cody, D, Flynn, M, Calculation of Individualized Organ Dose for CT Patients in National Lung Screening Trial.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14011196.html