Dosimetric effects of target volume delineation with metal clip and seroma, alone or in combination, on external-beam partial breast irradiation: a study based on four-dimensional computed tomography

Abstract

Objective To evaluate the dosimetric effects of target volume delineation with metal clip and seroma, alone or in combination, on external-beam partial breast irradiation (EB-PBI) based on four-dimensional computed tomography (4DCT). Methods Twenty female patients undergoing EB-PBI from 2009 to 2013 were enrolled as subjects. The gross tumor volumes (GTVS), GTVC, GTVS, and GTVC+ S, were delineated on 4DCT images at 10 phases using metal clip, seroma, and both of them, respectively. The GTVS on 4DCT images at 10 phases were fused to generate the internal gross tumor volumes (IGTVS), IGTVC, IGTVS, and IGTVC+ S. The planning target volumes (PTVS), PTVC, PTVS, and PTVC+ S, were obtained via expansion of margin by 15 mm. The three-dimensional conformal radiotherapy plans were made by one physician based on PTVC, PTVS, and PTVC+ S on end-inhalation images. The target volume, homogeneity index (HI), conformity index (CI), and doses to organs at risk were compared between the three groups. Results The C+ S group had the largest IGTV, PTV, and the ratio of PTV to diseased breast volume, which was followed by the C group and the S group (all P 0.05). Conclusions The volume variation caused by target volume delineation on 4DCT images based on different references has little impact on dose distribution in target volume. However, it has substantial impact on radiation doses to the ipsilateral normal breast and lung. Key words: External-beam partial breast irradiation; Tmography, X-ray computed, four-dimensional; Surgical clips; Seroma; Target determination