Room: Track 1
Purpose: To create the tube current modulation (TCM) profiles from a series of reference computational human phantoms representing pediatric and adult males and females and to implement the results into an existing organ dose calculation program for computed tomography (CT) patients.
Methods: We created TCM profiles from the twelve International Commission on Radiological Protection (ICRP) reference pediatric and adult phantoms by using a ray-tracing algorithm (Li et al. PMB 2014) and x-ray spectra for a Siemens CT scanner. We averaged angular modulation in a single rotation to derive surrogate longitudinal modulation profiles with 10 mm interval from the top of the head to the bottom of the feet in each phantom. The TCM profiles were created for different x-ray spectra (80, 100, and 120 kVp) and filtrations (head and body) as well as four different modulation strength levels ranging from 0 to 1. The resulting profiles were implemented into an existing CT organ dose calculation program, National Cancer Institute dosimetry system for CT (NCICT). We compared organ doses for different scan protocols between fixed tube current and TCM scans.
Results: The ratio of modulated mA to reference mA varied from 0.6 to 3.2 when at the maximum modulation strength of 1 in case of the ICRP adult male phantom. The minimum and maximum ratios were observed around the phantom’s abdominal and shoulder regions, respectively. Organ dose reduction by using TCM compared to no TCM scans was up to 20% (small intestines) at the modulation strength of 1, followed by the heart wall (17%) and colon (13%).
Conclusion: A library of theoretical TCM profiles were established using a generic ray-tracing algorithm and implemented into the NCICT organ dose calculator. The new feature should facilitate more accurate estimation of organ doses for pediatric and adult CT patients.
Funding Support, Disclosures, and Conflict of Interest: Software licensed to PACS Health