Objective To comprehensively and accurately analyze the out-performance of low-dose chest CT (LDCT) vs. standard-dose CT (SDCT). Methods The image quality, size measurements and radiation exposure for LDCT and SDCT protocols were evaluated. A total of 117 patients with extra-thoracic malignancies were prospectively enrolled for non-enhanced CT scanning using LDCT and SDCT protocols. Three experienced radiologists evaluated subjective image quality independently using a 5-point score system. Nodule detection efficiency was compared between LDCT and SDCT based on nodule characteristics (size and volume). Radiation metrics and organ doses were analyzed using Radimetrics. Results The images acquired with the LDCT protocol yielded comparable quality to those acquired with the SDCT protocol. The sensitivity of LDCT for the detection of pulmonary nodules (n=650) was lower than that of SDCT (n=660). There was no significant difference in the diameter and volume of pulmonary nodules between LDCT and SDCT (for BMI <22 kg/m(2), 4.37 vs. 4.46 mm, and 43.66 vs. 46.36 mm(3); for BMI >= 22 kg/m(2), 4.3 vs. 4.41 mm, and 41.66 vs. 44.86 mm(3)) (P>0.05). The individualized volume CT dose index (CTDIvol), the size specific dose estimate and effective dose were significantly reduced in the LDCT group compared with the SDCT group (all P<0.0001). This was especially true for dose-sensitive organs such as the lung (for BMI <22 kg/m(2), 2.62 vs. 12.54 mSV, and for BMI >= 22 kg/m(2), 1.62 vs. 9.79 mSV) and the breast (for BMI <22 kg/m(2), 2.52 vs. 10.93 mSV, and for BMI >= 22 kg/m(2), 1.53 vs. 9.01 mSV) (P<0.0001). Conclusion These results suggest that with the increases in image noise, LDCT and SDCT exhibited a comparable image quality and sensitivity. The LDCT protocol for chest scans may reduce radiation exposure by about 80% compared to the SDCT protocol.