Objective  To compare the positioning errors fixed by vacuum bag and breast bracket, and to explore the feasibility of vacuum bag in posture fixation for postoperative radiotherapy breast cancer patients with total mastectomy.

  Methods  Retrospective analysis of data of 78 postoperative radiotherapy patients with breast cancer was performed, including 42 patients with posture fixation by breast bracket (breast bracket group), and 36 patients using vacuum bag for body position fixation (vacuum bag group). Cone-beam computed tomograpgy(CBCT) image registrations were used for 1 time to 2 times per week during radiotherapy so as to obtain more accurate data. The right, left, forward, backward, up, down directions positioning errors were collected. And planning target volume margin was calculated by the formula.

  Results  The positioning errors of the breast bracket group in left, forward and up directions were (0.34±0.24), (-0.36±0.33), and (-0.44±0.29) cm, respectively, and were (0.26±0.27), (-0.28±0.18), (-0.29±0.20) cm, respectively in the vacuum bag group. The positioning error of the vacuum bag group was less than that of the breast carrier group (P < 0.05). The calculated planning target volume margin of the breast bracket group in right, left, forward, backward, up, down directions were 0.40, 0.49, 0.81, 1.21, 0.62, 0.70 cm, respectively, and 0.39, 0.57, 0.32, 0.55, 0.41, 0.64 cm, respectively in the vacuum bag group.

  Conclusion  For breast cancer patients with postoperative radiotherapy, vacuum bag and breast bracket can be both accepted in clinic, but vacuum bag has less positioning error and higher accuracy in treatment.