Background and Objectives: The objectives of this study were to test the feasibility of sole interstitial high-dose-rate brachytherapy (HDR-BT) after breast-conserving surgery (BCS) for T1 breast cancer in a phase I-II study, and to present the initial findings of a phase III trial comparing the efficacy of tumor bed radiotherapy (TBRT) alone with conventional whole breast radiotherapy (WBRT). Methods: Forty-five prospectively selected patients with T1 breast cancer undergoing BCS were enrolled into a phase I-II study of TBRT alone, using interstitial HDR implants. HDR-BT of 7 × 4.33 Gy (n = 8) and 7 × 5.2 Gy (n = 37) was delivered to the tumor bed. Based on the results of this phase I-II study, a further 126 patients were randomized to receive 50 Gy WBRT (n = 63) or TBRT alone (n = 63); the latter consisted of either 7 × 5.2 Gy HDR-BT (n = 46) or 50-Gy wide-field electron irradiation (n = 17). Breast cancer related events and side effects were assessed. Results: In the phase I-II study, at a median follow-up of 57 months, 2 (4.4%) local, 3 (6.7%) axillary, and 3 (6.7%) distant failures were observed. Two patients (4.4%) died of breast cancer. The 5-year probability of cancer-specific, relapse-free and local recurrence-free survival was 90.0%, 85.9%, and 95.6%, respectively. The cosmetic results were judged to be excellent in 44 of 45 patients (97.8%). Severe (higher than grade 2) skin sequelae or fibrosis was not found. Symptomatic fat necrosis occurred in one patient (2.2%). In the phase III study, at a median follow-up of 30 months, the locoregional tumor control was 100% in both arms. The 3-year probability of cancer-specific and relapse-free survival was 98.1% and 98.4% in the WBRT group and 100% and 94.4% in the TBRT group, respectively (P = NS). There was no significant difference between the two treatment arms regarding the incidence of radiation side effects. Conclusions: Five-year results of our phase I-II study prove that sole HDR-BT of the tumor bed with careful patient selection and adequate quality assurance is a feasible alternative to WBRT. However, long-term results of phase III trials are required to determine the equivalence of TBRT alone, compared with WBRT in the management of selected patients with early breast cancer.
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