A phase II trial of brachytherapy alone following lumpectomy for stage I or II breast cancer: initial outcomes of RTOG 9517

565 Background: In order to shorten the conventional 6–7 week radiation treatment time, and to treat only the tissue at greatest risk for recurrence, this phase II trial evaluates partial breast irradiation with 4–5 days of interstitial brachytherapy as an alternative to external beam. Methods: Eligibility criteria included patients (pts) with invasive ≤ 3cm non-lobular carcinoma, 0–3 positive axillary nodes with no extracapsular extension and at least 6 nodes removed, negative surgical margins, no residual suspicious microcalcifications, no extensive intraductal component, and no collagen vascular disease. After lumpectomy and axillary dissection, pts were treated with either high (34 Gy in 10 fractions over 5 days) or low (45 Gy in 3.5–5 days) dose rate (HDR or LDR) brachytherapy. Treatment volume was the lumpectomy cavity plus 2cm, except where limited by chest wall or skin. Systemic therapy was given after brachytherapy at physician discretion. Endpoints included local and regional control, disease-free (DFS) and overall survival (OS). Results: One hundred pts were enrolled and one was ineligible because only a sentinel node was removed. Median follow-up is 3.7 years, range 0.6–5.7. Eighty-seven pts had T1 and 12 had T2 tumors. Seventy-nine were pathologically N0 and 20 were N1. The actuarial 4-year breast and nodal recurrence rate is 3% (3 pts, all HDR, T1N0 x2 and T1N1) and 3% (2 pts, both HDR, T1N0 x2), respectively. Distant metastasis occurred in 6 pts, 3 T1N0 and 3 T2N1, for an actuarial 4-year rate of 6%, HDR 8% and LDR 4%. DFS and OS were 85% and 93% at 4 years (82% and 95% HDR, 90% and 90% LDR). Contralateral breast cancer developed in 3 pts, 1 HDR and 2 LDR. Six pts had non-breast second primaries, 4 HDR and 2 LDR. Conclusions: We conclude that partial breast brachytherapy on this RTOG trial yields excellent tumor control at this early analysis (<1% local failure per year), warranting support for a future phase III trial. Author Disclosure Employment or Leadership Consultant or Advisory Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration Nucletron Proxima Therapeutics