Figure 2. Radiotherapy (RT) Boost by Patient Characteristic.

Patients are compared between those who received an RT boost (boost group) vs those who did not (no-boost group), with additional stratification by characteristics. A, Negative (−) margin status indicates the National Surgical Adjuvant Breast Project B-17 definition of no ink on tumor; positive (+) margin status, ink on tumor. B, Margins were stratified using the Society of Surgical Oncology/American Society of Radiation Oncology definition of at least 2.0 vs less than 2.0 mm. The benefit of the RT boost in decreasing ipsilateral breast tumor recurrence (IBTR) is apparent in patients with margins of at least 2.0 mm but is not significant in patients with margins of less than 2.0 mm. C, Patients with negative margins were stratified by those younger than 50 years vs 50 years or older. IBTR estimates are significantly lower with the delivery of an RT boost relative to no boost.

^aP value was calculated with control by confounders.