Irradiation in early-stage breast cancer: conventional whole-breast, accelerated partial-breast, and accelerated whole-breast strategies compared.

Whole-breast irradiation (WBI) following breast-conserving surgery (BCS) has been used for several decades as an alternative to mastectomy in the treatment of localized breast cancer, and it has been shown to decrease rates of local-regional recurrence and improve survival rates compared with BCS alone. WBI is delivered using high-energy external beam radiation and typically consists of approximately 5 weeks of daily treatments to the entire breast, with or without inclusion of a "boost" to the primary site. Accelerated partial-breast irradiation (APBI) and accelerated whole-breast irradiation (AWBI) have been developed as alternatives to conventional WBI for selected patients with early-stage breast cancer. Given its large size and long follow-up, the Canadian trial of AWBI has been widely considered as practice-changing, and additional studies of AWBI are maturing or newly-launched. Use of APBI is based on the observation that the majority of local recurrences occur near the primary tumor site. Because a smaller portion of the breast is irradiated, treatment courses can often be abbreviated, and techniques such as conformal external beam, catheter- or balloon-based brachytherapy, and intra-operative radiation have been developed. Data from early APBI randomized trials and retrospective studies report mixed results. However, given the protracted time to local recurrence and complications following breast-conserving therapy, definitive results from contemporary randomized clinical trials comparing conventional WBI against AWBI or APBI are still limited.