The Effectiveness of Intraoperative Clip Placement in Improving Radiation Therapy Boost Targeting After Oncoplastic Surgery.

PURPOSE: The role of surgical clips as markers of the tumor bed cavity for radiation therapy boost targeting after oncoplastic surgery is not well understood. Therefore, we sought to evaluate whether the placement of surgical clips can reduce interobserver variability in the delineation of the tumor bed cavities of oncoplastic surgery patients and ultimately determine an optimal number of clips to place.

METHODS AND MATERIALS: We reviewed records of 39 women with breast cancer who underwent oncoplastic breast surgery and adjuvant radiation therapy at our institution. Three radiation oncologists contoured tumor bed cavity volumes on planning computed tomography simulation images. Interobserver variability was measured both by a coefficient of variation of radiation oncologists contour volume and a concordance index 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 1-way analysis of variance. 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 concordance index was significantly reduced in patients who received intraoperative surgical clips (F = 5.755; P = .001). A similar trend was seen in contour volume (F = 2.616; P = .052). Results of 1-way analysis of variance and post hoc analysis showed that 4 clips are effective and sufficient for reproducible delineation of the tumor bed cavity for the radiation therapy boost. Increasing excision volume does not result in an increase in interobserver variability (r2  = 0.00003).

CONCLUSIONS: In oncoplastic surgery patients, intraoperative placement of surgical clips is beneficial and effective in improving the delineation of the tumor bed cavity for the radiation therapy boost. Four clips are necessary and sufficient for accurate boost targeting after lumpectomy with oncoplastic reconstruction.