Background
Secondary analysis of radiotherapy fields used in ACOSOG Z0011 patients. Radiation field data were reviewed for 228 patients treated at multiple institutions participating in the Z0011 trial. The objective was to characterize what axillary volumes were irradiated in this trial, which randomized patients with 1-2 positive SLNs undergoing BCS to SLNB alone vs ALND.
Interventions and follow up
Arm A: Fields reviewed from SLNB-only arm of Z0011
Arm B: Fields reviewed from ALND arm of Z0011
Primary endpoint: Proportion of patients receiving high tangents (covering lower axilla) or deliberate third-field nodal RT
mFollow up: N/A — field review study
Arm B: Fields reviewed from ALND arm of Z0011
Primary endpoint: Proportion of patients receiving high tangents (covering lower axilla) or deliberate third-field nodal RT
mFollow up: N/A — field review study
Results
Intentional nodal RT (third-field or supraclavicular): 18.9% of patients in SLNB arm; 17.1% in ALND arm
High tangents (unintentional lower axillary coverage): ~50% of patients in both arms received tangent fields extending into level I/II axilla
Total with any axillary coverage: Majority of patients received some level of axillary irradiation through standard WBI fields
High tangents (unintentional lower axillary coverage): ~50% of patients in both arms received tangent fields extending into level I/II axilla
Total with any axillary coverage: Majority of patients received some level of axillary irradiation through standard WBI fields
Adverse events
Main adverse events: Not a treatment study; no AE data collected.
Conclusions
A substantial proportion of Z0011 patients received either deliberate nodal RT or inadvertent axillary coverage through high tangent fields. This axillary irradiation may have contributed to the low axillary failure rates observed in the SLNB arm, partially explaining why ALND could be safely omitted. The safety of SLNB omission in Z0011 may not be fully generalizable to settings where standard low tangents are used without any axillary coverage.
Key Limitations
Key Limitations: Field review was not part of the Z0011 protocol — radiation technique was not standardized. Only 228 of 891 randomized patients had RT fields reviewed. Classification of "high tangent" was not uniform. Cannot establish causality between axillary irradiation and outcomes in Z0011 from this secondary analysis alone.
Clinical Context
This paper is critical for interpreting Z0011: it reveals that the "sentinel lymph node biopsy alone" arm was not truly a "no axillary treatment" arm for many patients. This supports the concept that regional nodal irradiation (RNI) covering the low axilla may be sufficient for disease control in patients with limited nodal involvement, and informs subsequent studies like ALLIANCE Z11102 and AMAROS. It also supports intentional use of high tangents or formal nodal RT in patients with positive SLNs who do not undergo ALND.
References