The place of the boost in the breast cancer treatment: State of art

Several randomized controlled trials have demonstrated the benefit of a boost to the tumor bed (TB) to reduce the risk of ipsilateral breast tumor recurrence. Recent technological progress has facilitated improved conformation of isodoses around the target volume. The accuracy and reproducibility of TB delineation have become even more essential. The purpose of this study is to review the extant knowledge on the boost delineation in breast cancer, focusing on interobserver variability (IOV) and the influence of various factors, such as the presence of clips or different imaging modalities to improve IOV. Most studies investigating IOV for boost delineation have shown poor reproducibility (with comparison indices such as the dice similarity index around 0.5). Clips in the lumpectomy cavity (LC), postoperative fluid accumulation in the LC and/or high cavity visualization score appeared to be associated with improved IOV. Likewise, the use of preoperative imaging (CT and/or MRI) may also be useful in improving the accuracy of TB definition but without any real gain in terms of IOV. Moreover, the delineation of boost has become even more challenging since the development of oncoplastic surgery. To improve the reproducibility and the accuracy of boost delineation, this review suggests that within each center, a group of multidisciplinary experts, including surgeons, radiation oncologists, pathologists, and radiologists, should convene to develop local guidelines, which may include the choice of preoperative imaging, the number and location of surgical clips, pathological margins, and orientation. The elaboration of contouring atlas is certainly of great assistance.