Risk-Adapted Target Delineation for Breast Cancer: Controversies and Considerations

Abstract

The advent of computed tomography-based planning coupled with modern tools for target delineation and hypofractionated treatment schedules has increased efficiency and throughput for patients with breast cancer. While the benefit of adjuvant radiation therapy (RT) in reducing locoregional recurrences is established, disentangling local versus regional recurrence risks with modern treatment protocols has become an area of active research to de-escalate treatment. Delineation guidelines for nodal regions either attempt to replicate results of conventional RT techniques by translating bony landmarks to clinical target volumes or use landmarks based on the fact that lymphatic channels run along the vasculature. Because direct comparisons of both approaches are implausible, mapping studies of nodal recurrences have reported on the proportion of nodes included in these delineation guidelines, and larger, bony, landmark-based guidelines appear intuitively appealing for patients with unfavorable risk factors. A pooled analysis of these studies is reported here, along with literature supporting the exclusion of the true chest wall from postmastectomy/breast-conserving surgery clinical target volumes and the selective (versus routine) use of bolus during postmastectomy RT. The risk-adapted approach suggested here accounts for the risk of recurrence as well as toxicity and endorses nuanced target volume delineation rather than a one-size-fits-all approach.