OBJECTIVE Currently, cardiac interventional radiology equipment has tended toward using flat-panel detectors (FPDs) instead of image intensifiers (IIs) because FPDs offer better imaging performance. However, the radiation dose from an FPD in cardiac interventional radiology is not clear. The purpose of our study was to measure the radiation doses during cineangiography and fluoroscopy of many cardiac radiology systems that use FPDs or IIs, in clinical settings. METHODS This study examined 20 radiology systems in 15 cardiac catheterization laboratories (11 used FPD and nine used II). The entrance surface doses with digital cineangiography and fluoroscopy were compared for the 20 systems using acrylic plates (20-cm thick) and a skin dose monitor. RESULTS For fluoroscopy, the average entrance surface doses of the 20-cm-thick acrylic plates were identical for FPD (average +/- SD, 16.63 +/- 7.89 mGy/min; range, 5.7-26.4 mGy/min; maximum/minimum, 4.63) and II (17.81 +/- 12.52 mGy/min; range, 6.5-42.2 mGy/min; maximum/minimum, 6.49) (p = 0.799). For digital cineangiography, the average entrance surface dose of the 20-cm-thick acrylic plate was slightly lower with FPD (29.68 +/- 16.40 mGy/10 s; range, 8.9-58.5 mGy/10 s; maximum/minimum, 6.57) than with II (38.50 +/- 33.71 mGy/10 s; range, 15.2-117.1 mGy/10 s; maximum/minimum, 7.70), although the difference was not significant (p = 0.487). CONCLUSIONS We found that the average entrance doses of cineangiography and fluoroscopy in FPD systems were not significantly different from those in II systems. Hence, FPDs did not inherently reduce the radiation dose, although FPDs possess good detective quantum efficiency. Therefore, to reduce the radiation dose of cardiac interventional radiology systems, even FPD systems, practical measures are necessary.