Background/Objectives: We quantitatively evaluated respiratory-induced clinical target volume (CTV) motion during postoperative whole-breast radiotherapy in patients undergoing breast-conserving surgery (BCS) using four-dimensional computed tomography (4DCT) and determined the internal margins for assessing respiratory motion. Materials and Methods: We enrolled 100 patients who underwent postoperative whole-breast breast RT after BCS. Simulation CT was performed using 4DCT, and the CTV was delineated for the 10 respiratory phases (0–90%). CTV center displacement was measured in the lateral, anteroposterior, and superoinferior directions and three-dimensional (3D) vector magnitudes were calculated. Internal margins for respiratory motion were calculated using the Van Herk formula (2.5Σ + 0.7σ). Results: Mean CTV center displacement (mm) was 0.94 ± 0.52 (lateral), 1.29 ± 0.59 (anteroposterior), and 1.00 ± 0.51 (superoinferior). The mean 3D vector magnitude was 1.99 ± 0.68 (range, 0.70–3.51) mm. Anteroposterior motion was significantly greater than the lateral and superoinferior motion (p < 0.001). No patient exhibited motion exceeding 3 mm in any direction. Right-breast 3D motion was significantly larger than the left-breast motion (2.17 ± 0.66 vs. 1.82 ± 0.65 mm, p = 0.008). Internal margins (mm) for respiratory motion were 1.02 (lateral), 1.24 (anteroposterior), and 1.03 (superoinferior). Conclusions: Respiratory-induced CTV motion during whole-breast RT after BCS was small, with anteroposterior dominance. Calculated internal margins were approximately 1 mm in all directions, suggesting that a conventional 5 mm CTV-to-planning target volume (PTV) margin is adequate to compensate for respiratory motion and indicating that routine 4DCT or respiratory motion management may be unnecessary for target coverage.
Jo et al. (Thu,) studied this question.
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