A comparative study on the volume and localization of the internal gross target volume defined using the seroma and surgical clips based on 4DCT scan for external-beam partial breast irradiation after breast conserving surgery

BACKGROUND To explore the volume and localization of the internal gross target volume defined using the seroma and/or surgical clips based on the four-dimensional computed tomography (4DCT) during free-breathing. METHODS Fifteen breast cancer patients after breast-conserving surgery (BCS) were recruited for EB-PBI. On the ten sets CT images, the gross target volume formed by the clips, the seroma, both the clips and seroma delineated by one radiation oncologist and defined as GTVc, GTVs and GTVc+s, respectively. The ten GTVc, GTVs and GTVc+s on the ten sets CT images produced the IGTVc, IGTVs, IGTVc+s, respectively. The IGTV volume and the distance between the center of IGTVc, IGTVs, IGTVc+s were all recorded. Conformity index (CI), degree of inclusion (DI) were calculated for IGTV/IGTV, respectively. RESULTS The volume of IGTVc+s were significantly larger than the IGTVc and IGTVs (p<0.05). There was significant difference between the DIs of IGTVc vs IGTVc+s, the DIs of IGTVs vs IGTVc+s. There was significant difference among the CIs of IGTV/IGTV. The DIs and CIs of IGTV/IGTV were negatively correlated with their centroid distance (r<0, p<0.05). CONCLUSIONS There were volume difference and spatial mismatch between the IGTVs delineated based on the surgical clips and seroma. The IGTV defined as the seroma and surgical clips provided the best overall representation of the 'true' moving GTV.