The Effectiveness of Intra-Operative Clip Placement in Improving Radiotherapy Boost Targeting Following Oncoplastic Surgery.

Abstract Purpose The role of surgical clips as markers of the tumor bed cavity for radiotherapy boost targeting after oncoplastic surgery is not well understood. Therefore, we sought to evaluate whether the placement of surgical clips can reduce inter-observer variability in the delineation of the tumor bed cavities of oncoplastic surgery patients and ultimately, determine an optimal number of clips to place. Methods We reviewed records of 39 women with breast cancer who underwent oncoplastic breast surgery and adjuvant radiotherapy at our institution. Three radiation oncologists (RO) contoured tumor bed cavity volumes on planning computed tomography simulation images. Inter-observer variability was measured both by a coefficient of variation of RO contour volume (COVTBV) and a concordance index (CI) defined as the quotient of the intersecting and aggregated volume of the contours. Patients were stratified by the number of surgical clips placed and compared by one-way ANOVA. Simple linear regression was used to evaluate the relationship of total excised volume and interobserver variability in patients with a sufficient quantity of surgical clips. Results Interobserver variability in the delineation of the tumor bed cavity as measured by CI was significantly reduced in patients who received intra-operative surgical clips (F = 5.755, p = 0.001). A similar trend was seen in COVTBV (F = 2.616 p = 0.052). Results of one-way ANOVA and post-hoc analysis showed that 4 clips are effective and sufficient for reproducible delineation of the tumor bed cavity for the radiotherapy boost. Increasing excision volume does not result in an increase in inter-observer variability (r2 = 0.00003). Conclusions In oncoplastic surgery patients, intra-operative placement of surgical clips is beneficial and effective in improving the delineation of the tumor bed cavity for the radiotherapy boost. Four clips are necessary and sufficient for accurate boost targeting following lumpectomy with oncoplastic reconstruction.