RecruitingPhase 3Radiation therapyIntensity Modulated Radiotherapy (IMRT) vs. 3D-conformal Accelerated Partial Breast Irradiation (APBI) for Early Stage Breast Cancer After LumpectomyIn the setting of radiotherapy as part of breast-conservation therapy for patients with early stage breast cancer, the novel planning and delivery method of intensity modulated radiotherapy is an effective and safe alternative to the commonly-used standard 3D-conformal external beam radiotherapy, spares more normal breast and lung tissue, and may lead to improved clinical outcomes.