The purpose of this study was to demonstrate CTDI estimation using GATE simulations, and to extend its techniques to
various CT applications. We simulated various phantom sizes to estimate CTDI100 values for different patients. The
simulations were performed using a single axial scan using standard PMMA (polymethylmethacrylate) head and body
phantoms. Simulations of exposure in air were performed to compare simulated results with physically measured data.
Simulations of absorbed dose in PMMA digital phantoms were performed to compare simulated results with physically
measured data in corresponding PMMA physical phantoms at 5 different positions (at center, and 12hr, 3hr, 6hr, 9hr
positions in phantoms). Additional simulations were performed for PMMA digital phantoms of various diameters (1-50
cm) at various kVp (80, 100, 120, 140 kVp) and mAs (100, 200, 300, 400 mAs) levels. For the PMMA head and body
phantoms, the results of simulations showed an agreement with measured data by a maximum percent difference of 8.3%
(head), 4.2% (body) for all energies applied. For the different positions, the results of simulations showed an agreement
with measured data by a maximum per position difference of 4.7% (head), 5.1% (body) for 120 kVp. Within these
limitations, for both various kVp and mAs levels, the results showed that CTDI100 values nonlinearly decreased as a
function of diameter. For various diameters, the results showed that the CTDI100 values nonlinearly and linearly
increased as a function of kVp and mAs, respectively.