Correlations between displacements of GTV, surgical clips, and skin markers in external-beam partial breast irradiation: a study based on 4DCT

Objective: To investigate the correlations between the displacements of surgical clips, skin markers and the gross tumor volume (GTV) delineated by surgical clip and seroma based on four-dimensional computed tomography (4DCT) during normal breathing. Methods: On each of the 10 respiratory phases of 4DCT with 15 patients of breast cancer, the surgical cavity, which was defined as GTV and formed by both surgical clips and seroma, all surgical clips in the cavity, and skin markers on the skin were delineated by the same radiation oncologist. The center displacements of GTV, selected boundary surgical clips and skin markers in the left-right (LR), anterior-posterior (AP), and superior-inferior (SI) directions were recorded and analyzed by Pearson method. Results: In the AP direction, there was a positive correlation between the displacements of the GTV and the inner clip (r = 0.643, P = 0.013). In the SI direction, the displacement of GTV was positively correlated with those of the lower clip and the skin marker at anterior body midline (r = 0.857 and 0.643, P = 0.002 and 0.013). In the LR and AP directions, there was a positive correlation between the displacements of the outer clip and the ipsilateral skin marker (r = 0.757 and 0.697, P = 0.001 and 0.025), but they were negatively correlated with each other in the SI direction (r = -0.647, P = 0.043). In the AP direction, there was a positive correlation between the displacements of the inner clip and the skin marker at the anterior body midline (r = 0.738, P = 0.015). Conclusions: The correlations between the displacement of GTV delineated by surgical clips and seroma and the displacements of surgical slips and skin markers vary under different conditions, and so does the correlation between the displacements of surgical clips and skin markers. (authors)