Statistical Analyses
HEART
All CBCT images were analyzed to assess whether the heart was displaced away from the chest in a manner consistent with the DIBH-planned images. The CBCT images were uploaded to the planning system and registered with the planning CTs based on the breast target. The heart during treatment was contoured on the CBCT ((A, upper left) Heart contour on the voluntary deep inspiration breath-hold (VDIBH)-planned computed tomography (CT) (brown); (B, upper right) heart contour on cone beam computed tomography (CBCT) (yellow); (C, lower middle) all heart contours from CBCT images registered to the voluntary deep inspiration breath-hold (VDIBH)-planned CT of one patient for heart position and heart dose evaluation.A predesigned questionnaire was completed by patients and involved radiotherapists to assess the acceptance of this technique. The translational set up errors were calculated by comparing CBCT with planning CT, and the planning target volume margins were calculated using the following formula: 2.5Σ + 0.7δ, wherein Σ and δ represent the standard deviations of the systematic and random errors, respectively.