This study was designed to investigate the effect of the different topograms (AP and dual AP/Lateral) on patient dose indices and image quality in thorax and abdomen-pelvis CT. Size-specific dose estimation (SSDE), volumetric CT dose index (CTDIvol), milliampere seconds (mAs), effective dose, as well as signal to noise ratio (SNR) and contrast to noise ratio (CNR) of 60 thorax and 60 abdomen-pelvis CT scans were analyzed. In thorax CT, SSDE, mAs, CTDIvol and effective dose were significantly reduced by using dual topograms (p < 0.05) but not significantly reduced in abdominal-pelvic scans (p > 0.05). There was no significant difference between CNR parameter in the two groups for thorax CT (p > 0.05) and SNR parameter in abdomen-pelvic CT (p < 0.05) and all images were diagnostically acceptable. The use of two topograms in thorax CT is an efficient approach to reduce dose indices without decreasing the image quality.