[en] Objective: To investigate the dosimetric differences among three types of breath hold mode (free breath: FB, thoracic deep inspiration breath hold: T-DIBH, abdomen deep inspiration breath hold: A-DIBH) and to explore the optimal breath hold method in the postoperative radiotherapy of left-side breast cancer patients with minimum dose to normal tissues and organs at risk. Methods: A total of eighteen patients with left-side breast cancer patients who underwent postoperative radiotherapy were enrolled in this study. Three CT simulation scans with three different breath hold method (FB, T-DIBH, and A-DIBH) were performed for each patient. Dosimetric differences were compared among plans generated on these three different CT image sets. Results: There was no significant difference in the volume, mean dose, and homogeneity of planning target volume (PTV) among plans generated from three different image sets (P > 0.05). The mean heart dose, mean LAD dose and mean ipsilateral lung dose in plans generated from CT image sets with FB, T-DIBH and A-DIBH were (3.21 ± 1.02), (1.74 ± 0.51),(1.31 ± 0.41) Gy (W = 171, P < 0.05), (34.61 ± 13.51), (14.38 ± 10.20), (9.21 ± 6.53) Gy (W = 171, P < 0.05), and (8.31 ± 2.75), (7.46 ± 1.96), (6.89 ± 1.79) Gy (W = 171, P < 0.05), respectively. Conclusions: Compared with plans with FB, plans with DIBH (T-DIBH and A-DIBH) achieved lower cardiac, LAD and pulmonary doses. A-DIBH achieved a better normal dose reduction than T-DIBH. (authors)