We investigated the detective quantum efficiency (DQE) of thin gadolinium
oxysulfide phosphor-based flat-panel detectors (FPDs) using cascaded-systems
analysis and Monte Carlo (MC) simulations for applications in megavoltage
(MV) x-ray industrial imaging. We decomposed the DQE formula into
(dose-independent) upper-limit DQE and (dose-dependent) DQE-reduction
factors. We obtained the absorbed energy distributions (AEDs) for
various x-ray detector designs and photon energies using MC simulations
and applied the AED analysis to the DQE formula. The investigations
examined include the x-ray-detector-only DQE and the effect of the
coupling efficiency between the x-ray detector and readout panel,
including electronic noise, on the upper-limit DQE. This study confirms
that the design of the metal build-up layer on the phosphor is effective
for MV imaging and emphasizes the importance of designing the readout
panel to maintain the upper-limit DQE. We expect the proposed DQE
analysis to be suitable for designing and evaluating FPDs for high-energy
nondestructive x-ray testing.