Axillary Irradiation with High Tangent Fields for Clinically Node-Negative Breast Cancer: Can 3-D Conformal Radiotherapy with a Field-in-Field Technique Better Control the Axilla?

Summary Background: The target volume for postoperative breast irradiation is the remaining breast tissue, and the axillary region is not an intentional target volume. Patients and Methods: Between 2001 and 2009, eligible women with pT1–2cN0/pN0(sn) breast cancer underwent breast­con­ serving therapy without axillary dissection. Treatment outcomes between 2 radiotherapy planning groups, high tangent fields with 2­dimensional (2­D) simulation­based planning and 3­dimensional (3­D) computed tomogra­ phy­based planning with a field­in­field technique, were compared. The correlating factors for axillary failure were also calculated. Results: In total, 678 patients were eligible. As of May 2009, the median follow­up times for the 2­D (n = 346) and 3­D (n = 332) groups were 94 and 52 months, respectively. Patient characteristics were bal­ anced, except for a younger population in the 2­D group and more lymphovascular invasion in the 3­D group. On multivariate analysis, 2­D planning was the only risk factor for axillary failure. In the 2­D and 3­D groups, the 5­year cumulative incidences of axillary failure were 8 (3.1%) and 1 (0.3%) (log­rank p = 0.009), respectively. The respective 5­year overall survival rates were 97.4 and 98.4% (p = 0.4). Conclusion: High tangent irradiation with 3­D planning improved axillary control compared to that with 2­D planning, suggesting that optimizing axillary dose distribution may impact outcomes.