To analyze the displacement of titanium clips for tumor bed localization after breast-conserving surgery for breast cancer and its influential factors.

A retrospective analysis was performed on the cone-beam computed tomography (CT) images of 14 patients with breast cancer who received radiotherapy after breast-conserving surgery from April to October, 2016.The relative position of the chest wall and the errors of the titanium clips in radiotherapy were measured. A Pearson correlation analysis was used to analyze the correlation of the displacement of titanium clips with the relative position of titanium clips, the breast volume, the vertical distance between the titanium clips and the tangential line of the chest wall, and the maximum thickness of the breast.

The system errors of the chest wall in left-right, superior-inferior, and anterior-posterior directions were 4.42, 3.44, and 5.13 mm, respectively, and the random errors were 3.55, 3.07, and 4.54 mm, respectively. The titanium clips had a large displacement relative to the chest wall, mainly in the left-right direction. The maximum system error was 4.39 mm and the random error was 2.42 mm. The displacement of titanium clips was not significantly correlated with the breast volume and the maximum thickness of the breast (P>0.05). However, the relative position of titanium clips in superior-inferior direction was significantly correlated with the displacement of the lowest, the most lateral, the most anterior, and the most posterior titanium clips (P<0.05). As to the uppermost clips, there was a significant difference in displacement between the clips close to the chest wall and the clips far from the chest wall (P=0.02).

Due to large setup error and displacement of titanium clips during radiotherapy, simultaneous integrated boost is not suitable for patients with breast cancer who are immobilized by vacuum cushion and received radiotherapy. The unstable immobilization may be the major influential factor for the displacement of titanium clips.

Tomography, X-ray computed, cone beam; Breast neoplasms/surgery; Variation of surgical clips