KEY POINTS
- This single-centre retrospective study included 100 consecutive patients undergoing postoperative whole-breast radiotherapy after breast-conserving surgery. All were simulated supine during free breathing using four-dimensional computed tomography divided into 10 respiratory phases.
- Mean clinical target volume centre displacement was 0.94 ± 0.52 mm laterally, 1.29 ± 0.59 mm anteroposteriorly, and 1.00 ± 0.51 mm superoinferiorly. Anteroposterior movement was significantly greater than movement in the other directions (p<0.001).
- No patient had displacement exceeding 3 mm in any individual direction. Mean three-dimensional displacement was 1.99 ± 0.68 mm, with a maximum of 3.51 mm.
- Respiratory internal margins calculated using the Van Herk formula were 1.02 mm laterally, 1.24 mm anteroposteriorly, and 1.03 mm superoinferiorly.
- Right-sided treatment and lower body mass index were independently associated with greater motion. The analysis measured only target centre displacement and did not evaluate deformation, dose distributions, interplay effects, or motion reproducibility during treatment.
CLINICAL TAKEAWAY
For supine, free-breathing postoperative whole-breast radiotherapy, respiratory motion contributed approximately 1 mm to the required margin, supporting the adequacy of a conventional 5 mm clinical target volume-to-planning target volume margin. The findings do not extend to regional nodal irradiation, boost treatments, prone positioning, postmastectomy radiotherapy, or ultrahypofractionation and remain technically relevant rather than practice-changing.