Planning the breast boost: How accurately do surgical clips represent the CT seroma?

Abstract: Background and purpose: To measure the distance between surgical clips and edge of CT-defined seroma in a coronal plane in women who have undergone wide local excision of breast cancer and to evaluate dosimetric coverage of CT-defined boost volumes by conventional clip-based electron fields. Materials and methods: Planning CT images of 30 lumpectomy cavities from 30 patients were reviewed. All seroma cavities had at least 4 clips and Cavity Visualization Score ⩾3. Distances between clips and seroma edge (D c–s) were measured at the radial margins for each patient. Clips-based electron fields were generated by including all the clips with 2cm margin in the coronal plane and three-dimensional conformal radiotherapy plans (3D-CRT) were devised based on CT tumor beds (CT-TBs). The parameters of dose–volume histogram between the two boost treatment plans were analyzed. Results: The mean seroma edge extended beyond the clips by 0.3–0.5cm. In all 120 D c–ss, 76.7% were ⩽0.5cm, 8.3% were >1cm and 15% were between 0.5 and 1cm. Twenty patients (20/30) had D c–smax (The maximal D c–s of each patient)>0.5cm and 7 patients had D c–smax >1cm. With the electron fields, only 46.7% (14/30) had D 90 (The minimal dose received by 90% of the planning target volume (PTV))>90% and geographical miss (any portion of the PTV receiving <50% of the prescribed dose) was found in 36.7% (11/30). D c–smax >0.5cm was associated with D 90 <90% (P <0.001) and >1cm was associated with geographic miss (P =0.001). Conclusions: Surgical clips are not always consistent with the edge of seroma. Electron boost field based on clips leads to insufficient dose coverage to the CT-TB. 3D-CRT planning should be considered to ameliorate the dose coverage to the tumor bed. [Copyright &y& Elsevier]