Background: There has been a rapid increase in the use of new radiation techniques for postlumpectomy radiation, including partial breast irradiation via brachytherapy (APBI-b), 3-dimentional conformal radiotherapy (3D-CRT), and intensity modulated radiotherapy (IMRT) techniques. However, it is unknown if these new radiation techniques provide survival benefit equivalent to external beam whole-breast irradiation (WBI) in patients undergoing breast conservation. Additionally, compliance with the 2009 ASTRO guidelines for partial breast radiation has not been examined in a contemporary cohort of patients.

Method: From the National Cancer Database, we identified 718,392 women diagnosed with AJCC stage 0-III breast cancer between 2003 and 2010, who underwent breast conserving surgery. Patients were classified into suitable, cautionary, or unsuitable for APBI-b according to ASTRO guidelines. Cox proportional hazard models were used to examine the effectiveness of the new irradiation modalities on overall survival in all eligible patients and within each ASTRO category.

Results: Overall, 37,363 patients (6.4%) underwent APBI-b, 40,767 (5.7%) underwent IMRT, 45,721 (6.4%) underwent 3D-CRT, 421,497 (58.7%) underwent conventional WBI. The utilization of the three new radiation techniques increased over the study period, and 31.3% of all patients treated with radiotherapy after lumpectomy actually used one of the three new methods in 2010. Overall, 35% of patients receiving APBI-b fell in the suitable category, 47% in the cautionary category, and 18% in the unsuitable category. After publication of the ASTRO guideline, the proportion of patients receiving APBI-b in the suitable category has increased from 34% in 2008 to 40% in 2010. After a median follow up of 46 months, 52,099 patients died. In invasive breast cancer patients, we found patients undergoing APBI-b had a 38% reduction in the risk of death, compared to patients without radiotherapy (hazard ratio, HR = 0.62, 95% CI: 0.57-0.66, p<0.001) after adjusting for age, tumor stage, tumor grade, hormone receptor status, race/ethnicity, insurance, and other clinical, pathologic, and facility factors. The adjusted HR was 0.63 (95% CI: 0.59-0.67, p<0.001) for IMRT, 0.60 (95% CI: 0.57-0.64, p<0.001) for 3D-CRT, and 0.62 (95% CI: 0.60-0.64, p<0.001) for conventional WBI. The effectiveness of the four radiation modalities was similar (p = 0.84). In the ASTRO suitable category, the HR of APBI-b was 0.70 (95% CI: 0.63-0.79), which is similar to the effect of APBI-b in the cautionary category (HR = 0.64, 95% CI: 0.56-0.73).

Conclusions: In a large cohort of women with early stage breast cancer, radiotherapy using three new techniques (APBI-b, IMRT, and 3D-CRT) was found to be as effective in reducing mortality as conventional whole breast irradiation. Although this is promising, long-term follow-up studies and randomized clinical trials are warranted.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P5-14-09.