Purpose: To report the 7-year results of a prospective study of accelerated partial breast irradiation (APBI) using interstitial high-dose-rate brachytherapy and compare the treatment results with those achieved by standard, whole breast radiotherapy (WBRT), with or without a tumor bed boost (TBB).
Methods and materials: Between 1996 and 1998, 45 prospectively selected patients with T1N0-N1mi (single nodal micrometastasis), nonlobular breast cancer without the presence of an extensive intraductal component and with negative surgical margins were treated with APBI using interstitial high-dose-rate implants. A total dose of 30.3 Gy (n = 8) and 36.4 Gy (n = 37) in seven fractions within 4 days was delivered to the tumor bed plus a 1-2-cm margin. During the same period, 80 patients, who met the eligibility criteria for APBI but who were treated with 50 Gy WBRT with (n = 36) or without (n = 44) a 10-16-Gy TBB, were selected as controls. The median follow-up for the APBI and control groups was 81 and 83 months, respectively. Local control, relapse-free survival, cancer-specific survival, late side effects, and cosmetic results were assessed.
Results: The crude rate of total ipsilateral breast failure was 6.7% (3 of 45), 11.4% (5 of 44), and 8.3% (3 of 36) for patients treated with APBI, WBRT, and WBRT + TBB, respectively. The differences in the 5- and 7-year actuarial rates of ipsilateral breast recurrence were not statistically significant among patients treated with APBI (4.4% and 9.0%), WBRT (4.7% and 14.8%), and WBRT + TBB (5.7% and 9.5%). No statistically significant difference in either the 7-year probability of relapse-free survival (79.8%, 73.5%, and 77.7% for APBI, WBRT, and WBRT + TBB, respectively) or cancer-specific survival (93.3%, 92.9%, and 93.9% for APBI, WBRT, and WBRT + TBB, respectively) was found. The 7-year actuarial elsewhere breast failure rate was 9.0% in the APBI group and 8.3% in the control group (p = 0.80). The rate of excellent/good cosmetic results was 84.4% in the APBI group and 68.3% in the control group (p = 0.04). The corresponding rates of asymptomatic fat necrosis were 20.0% and 20.6%. Symptomatic fat necrosis occurred in 1 patient (2.2%) treated with APBI. The incidence of Grade 2 or worse late radiation side effects was similar for both groups (26.7% vs. 28.6%).
Conclusion: Accelerated partial breast irradiation using interstitial high-dose-rate implants, with proper patient selection and quality assurance, yields similar 7-year results to those achieved with standard breast-conserving therapy. APBI does not increase the risk of elsewhere breast failures.