Intensity Modulated Radiotherapy (IMRT) vs. 3D-conformal Accelerated Partial Breast Irradiation (APBI) for Early Stage Breast Cancer After Lumpectomy

Inclusion Criteria:

* Histologically confirmed disease (AJC Classification): Tis, T1, T2 (≤ 3.0 cm), N0, M0.
* Microscopic multifocal disease is only allowed when the entire span of identified disease measures 3.0 cm or less.
* Negative surgical margins ( ≥ 0.2 cm) after final surgery.
* Subjects with infiltrating lobular histologies or high nuclear grade DCIS will be required to have breast MRI scanning as part of the initial staging to verify localized disease.
* Subjects with DCIS will be included in the study only if they had an MRI prior to lumpectomy.
* Findings on MRI scanning revealing relevant suspicion of disease outside of planned lumpectomy volume should be further evaluated by ultrasound and, if necessary biopsy, to exclude multicentric/multifocal disease.
* Subjects with malignant calcifications on mammography will be required to have repeat mammography after surgery to ensure removal of all malignant calcifications.
* Willing to complete additional screening requirements and meet eligibility criteria as defined in protocol Sec. 4.4.
* Successful placement of fiducial markers for IGRT requiring nonmigrating fiducials.
* PTV to ipsilateral breast ratio (IBR) ≤ 25 %.
* Radiotherapy anticipated to begin within 10 weeks of lumpectomy or re-excision of margins.

Exclusion Criteria:

* Pregnancy or breast-feeding.
* Have collagen-vascular disease.
* Inadequate surgical margins ( \< 0.2 cm) after final surgery.
* Subjects with persistent malignant/suspicious micro-calcifications.
* Gross multifocal disease and microscopic disease greater than 3.0 cm.