Background: High-resolution, low-noise detectors with minimal dead-space at chest-wall could improve posterior coverage and microcalcification visibility in dedicated cone-beam breast CT (CBBCT). However, their smaller field-of-view necessitates laterally-shifted detector geometry to enable optimizing the air-gap for x-ray scatter rejection. Objective: To evaluate laterally-shifted detector geometry for CBBCT with clinical projection datasets that provide for anatomical structures and lesions. Methods: CBBCT projection datasets (n=17 breasts) acquired with a 40x30-cm detector (1024x768-pixels, 0.388-mm pixels) were truncated along the fan-angle to emulate 20.3x30-cm, 22.2x30-cm and 24.1x30-cm detector formats and correspond to 20, 120, 220-pixels overlap in conjugate views, respectively. Feldkamp-Davis-Kress (FDK) algorithm with three different weighting schemes were used for reconstruction. Visual analysis for artifacts and quantitative analysis of root-mean-squared-error (RMSE), absolute difference between truncated and 40x30cm reconstructions (Diff), and its power spectrum (PS Diff) were performed. Results: Artifacts were observed for 20.3x30-cm, but not for other formats. The 24.1x30-cm provided the best quantitative results with RMSE and Diff (both in units of μ, cm-1) of 4.39x10-3 ±1.98x10-3 and 4.95x10-4 ±1.34x10-4 , respectively. The PS Diff (>0.3 cycles/mm) was in the order of 10-14 μ 2 mm 3 and was spatial-frequency independent. Conclusions: Laterally-shifted detector CBBCT with at least 220-pixels overlap in conjugate views (24.1x30-cm detector format), provides quantitatively accurate and artifact-free reconstruction.