In this work we investigated the benefit of the use of two lateral camera units additional to a central camera unit for 3D surface imaging for image guidance in deep-inspiration breath-hold (DIBH) radiotherapy by comparison with cone-beam computed tomography (CBCT). Ten patients who received DIBH radiotherapy after breast-conserving surgery were included. The performance of surface imaging using one and three camera units was compared to using CBCT for setup verification. Breast-surface registrations were performed for CBCT as well as for 3D surfaces, captured concurrently with CBCT, to planning CT. The resulting setup errors were compared with linear regression analysis. For the differences between setup errors an assessment of the group mean, systematic error, random error, and 95% limits of agreement was made. Correlations between derived surface-imaging [one camera unit;three camera units] and CBCT setup errors were: R2=[0.67;0.75], [0.76;0.87], [0.88;0.91] in left-right, cranio-caudal, and anterior-posterior direction, respectively. Group mean, systematic and random errors were slightly smaller (sub-millimeter differences) and the limits of agreement were 0.10 to 0.25cm tighter when using three camera units compared with one. For the majority of the data, the use of three camera units compared with one resulted in setup errors more similar to the CBCT derived setup errors for the craniocaudal and anterior-posterior directions (p<0.01, Wilcoxon-signed-ranks test). This study shows a better correlation and agreement between 3D surface imaging and CBCT when three camera units are used instead of one and further outlines the conditions under which the benefit of using three camera units is significant.