Abstract
BackgroundAccurate localisation of the lumpectomy cavity (LC) volume is one of the most critical points in 3D-conformal Partial breast irradiation (3D-APBI) treatment planning because the irradiated volume is restricted to a small breast volume. Here, we studied the role of the placement of surgical clips at the 4 cardinal points of the lumpectomy cavity in target delineation.MethodsForty CT-based 3D-APBI plans were retrieved on which a total of 4 radiation oncologists, two trainee and two experienced physicians, outlined the lumpectomy cavity. The inter-observer variability of LC contouring was assessed when the CTV was defined as the delineation that encompassed both surgical clips and remodelled breast tissue.ResultsThe conformity index of tumour bed delineation was significantly improved by the placement of surgical clips within the LC (median at 0.65). Furthermore, a better conformity index of LC was observed according to the experience of the physicians (median CI = 0.55 for trainee physicians vs 0.65 for experienced physicians).ConclusionsThe placement of surgical clips improved the accuracy of lumpectomy cavity delineation in 3D-APBI. However, a learning curve is needed to improve the conformity index of the lumpectomy cavity.
Highlights
Accurate localisation of the lumpectomy cavity (LC) volume is one of the most critical points in 3D-conformal Partial breast irradiation (3D-Accelerated Partial Breast Irradiation (APBI)) treatment planning because the irradiated volume is restricted to a small breast volume
In a previous study [5], we showed that surgical clips were needed to locate the lumpectomy cavity
We exclusively assessed inter-observer variability of LC delineation, focusing (i) on the entire CTV (CTV = surgical clips + remodelled breast tissue); (ii) only on the study of the CTV when it was restricted to the computed tomography (CT) slices which contained clips; and (iii) on the remodelled breast tissue
Summary
Accurate localisation of the lumpectomy cavity (LC) volume is one of the most critical points in 3D-conformal Partial breast irradiation (3D-APBI) treatment planning because the irradiated volume is restricted to a small breast volume. Accelerated Partial Breast Irradiation (APBI) is still under investigation to demonstrate equivalence to whole breast irradiation in terms of local control. Several issues related to this technique still warrant investigation: e.g. the identification and contouring of the lumpectomy cavity (LC), the patient's set-up and optimal dose determination. Unlike intra-operative partial breast irradiation, LC determination is critical as treatment delivery is delayed after breast surgery. In 3D-APBI, the GTV (Gross Tumour Volume) and CTV (Clinical Target Volume) are generally defined as the contouring of a seroma within the lumpectomy cavity, expanded by a 1 cm margin [2,3]. The delineation of the seroma could vary among different observers and even among experienced ones[4]
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