Recurrence rates for patients with early-stage breast cancer treated with IOERT at a community hospital per the ASTRO consensus statement for APBI

Abstract

Purpose: To report the recurrence rates after single-fraction intraoperative electron radiotherapy (IOERT) in patients with early-stage breast cancer treated on a single institution prospective Phase I/II protocol at a community hospital. Results were retrospectively analyzed according to suitability criteria from the updated American Society for Radiation Oncology (ASTRO) consensus statement for accelerated partial breast irradiation (APBI).

Methods and materials: Patients over 40 years with early-stage invasive or in situ breast cancer (<2.5 cm and node negative) were enrolled. IOERT 2100 cGy was delivered during breast conservation surgery, and patients were followed up for a median of 3 years (0.8-6.5 years) to determine toxicity and recurrence rates.

Results: Single-fraction IOERT was performed in 215 cases (6 bilateral treatments, 196 patients) with 13 patients receiving whole-breast radiation (WBR) after IOERT for adverse pathologic features. Of 202 cases of IOERT without WBR, 89 patients experienced an ipsilateral breast tumor recurrence (IBTR) giving a cumulative incidence of 3.96%. When the ASTRO APBI suitability criteria were applied, the IBTR rate was significantly lower for suitable patients vs. cautionary or unsuitable patients (1.6% vs. 3.4% vs. 21.0%, p = 0.0002). 3-year progression-free survival after IOERT alone was 93.4%. For patients who received standard WBR (4500-5040 cGy) after IOERT, no Grade 3 or 4 toxicities (acute or late) occurred and all patients are disease-free.

Conclusions: Single-fraction IOERT results in a low rate of IBTR when strictly adhering to ASTRO criteria for APBI suitability. Standard dose WBR for unfavorable pathologic results after 2100 cGy IOERT is well tolerated.

Keywords: APBI; ASTRO guideline; Breast cancer; IOERT; Recurrence.