Comparison of iridium implant boost versus electron boost as a component of breast conservation treatment for early-stage breast carcinoma.

CTRC-AACR San Antonio Breast Cancer Symposium: 2008 Abstracts Abstract #5144 Background: Breast conservation treatment includes lumpectomy followed by definitive radiation therapy, with radiation delivered to the whole breast followed by tumor bed boost. Currently, the boost is typically delivered by electron beams, but was previously delivered by iridium-192 implants. With re-emergence of implant radiotherapy techniques in current practice, long-term outcomes of both boost techniques are important. Methods: From 1977 to 1983, 141 patients with early-stage breast cancer were treated with iridium-192 boost after whole breast radiation. These patients were matched 1:1 to 141 patients who received electron boost from 1980 to 1990. Most implant patients were treated before widespread electron availability. Matching criteria included age at diagnosis, final pathologic margin status, pathologic tumor stage, and pathologic nodal stage. All patients had AJCC Stage I or II invasive breast carcinoma, had surgical excision of the primary tumor, and underwent definitive radiation to at least 60 grays. Chemotherapy was administered to 30 implant patients and 41 electron patients (p=0.014), and hormonal treatment to 3 implant patients and 12 electron patients (p=0.032). These systemic treatment variations were expected due to treatment era differences. Median follow-up was 16.7 years for implant patients (range 0.7-28.5) and 12.6 years for electron patients (range 1.4-25.4) (p<0.001). Results: Electron boost patients were more likely to have excellent/good cosmesis versus fair/poor cosmesis than implant boost patients. At 1-year follow-up, this was significant (p=0.014). This trend continued, with odds ratio of having excellent/good cosmesis versus fair/poor cosmesis in implant patients compared to electron patients being 0.29 after 5 years (95% CI 0.027-1.38, p=0.114) and 0.24 after 10 years (95% CI 0.005-1.93, p=0.266). Incidence of all complications evaluated did not differ between the two groups (all p≥0.07). Incidence of breast fibrosis was 3% per year in implant patients and 4% per year in electron patients (p=0.17). In total, breast fibrosis developed in 41% of implant patients and 16% of electron patients. Incidence of infection was 14% per year in the implant group and 6% per year in the electron group (p=0.09). In total, infection developed in 7% of implant patients and 9% of electron patients. Incidence of rib fracture was 2% per year in both groups (p=0.8). Incidence of cardiopulmonary complications was 4% per year in implant patients and 3% per year in electron patients (p=0.7). Incidence of non-cardiac vascular complications was 4% per year in both groups (p=0.1). Incidence of neuropathy was 4% per year in implant patients and 1% per year in electron patients (p=0.07). Conclusions: Patients treated with electron boost were more likely than those treated with implant boost to have excellent/good cosmesis, though this observation did not reach statistical significance at 5- and 10-year follow-up. Complication rates did not differ significantly between the groups with long-term follow-up. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 5144.