Long-Term Clinical and Cosmetic Outcomes of Once-Daily Accelerated Partial Breast Irradiation in Early Breast Cancer.

Purpose: Accelerated partial breast irradiation (APBI) is one of the standard treatment options in early-stage node negative breast cancer in selected patients. However, the optimal dose fractionation schedule still represents a challenge. We present the 12-year follow up results of clinical and cosmetic outcomes of once daily APBI with external beam radiation therapy which provides an APBI radiation dose equivalent to the whole breast radiation with a boost. Methods and Materials: From July 2008 to August 2010, we enrolled 34 patients with T1, T2 (< 3cm) N0 to receive once daily APBI with three dimensional conformal radiation therapy (3D-CRT) to a total dose of 49.95 Gy over 15 single daily fractions over 3 weeks at 3.33 Gy per fraction. Ipsilateral breast tumor recurrence (IBTR), acute toxicity, late toxicity and cosmesis was analyzed. The median follow-up for all patients is 144 months (12 years). Results: The median age of the patients was 61 years (range 46-83). Nine patients had ductal carcinoma in situ (DCIS) and 25 patients had invasive cancer. The median size of the tumor with DCIS pathology was 0.5 cm, while median size of the tumor with invasive cancer pathology was 1.0 cm. All of the patients had negative margins and negative nodes. Two IBTR was observed (5.8%). One patient had DCIS at recurrence and other had invasive recurrence. Two patients died due to non-cancer cause. The 12-year actuarial ipsilateral breast recurrence free survival was 93.5% and the 12-year actuarial overall survival was 93.2%. Late Grade 2 toxicity was observed in 6 patients and late grade 3 toxicity was seen in 1 patient. 91% of the patients had excellent to good cosmesis. Conclusions: This novel APBI dosing schema is based on an equivalent dose compared to whole breast radiation plus a tumor bed boost. This once daily APBI scheme is well-tolerated and demonstrates good to excellent cosmetic outcome and low rates of late complications on long term follow-up.