|Inclusion Criteria:||1) The patient must have stage 0, I, or II breast cancer. If stage II, the tumor size must be 3 cm or less.|
2) On histological examination, the tumor must be DCIS or invasive adenocarcinoma of the breast.
3) Surgical treatment of the breast must have been lumpectomy. The margins of the resected specimen must be histologically free of tumor (DCTS and invasive). Re- excision of surgical margins is permitted.
4) Gross disease must be unifocal with pathologic (invasive and/or DCIS) tumor size 3 cm or less. (Patients with microscopic multifocality are eligible as long as total pathologic tumor size is 3 cm or less.)
5) Patients with invasive breast cancer are required to have axillary staging which can include sentinel node biopsy alone (if sentinel node is negative), sentinel node biopsy followed by axillary dissection or sampling with a minimum total of 6 axillary nodes (if sentinel node is positive), or axillary dissection alone (with a minimum of 6 axillary nodes). (Axillary staging is not required for patients with DCIS.)
6) The patient must be randomized within 42 days following the last surgery for breast cancer (lumpectomy, re-excision of margins, or axillary staging procedure).
7) Patients must have an estrogen receptor (ER) analysis performed on the primary tumor prior to randomization. If ER analysis is negative, then progesterone receptor (PgR) analysis must be performed. If ER analysis is positive, PgR analysis is desired but not mandatory. ("Marginal" or "borderline" results [i.e., those not definitively negative] will be considered positive regardless of the methodology used.)
8) The target lumpectomy cavity must be clearly delineated and the target lumpectomy cavity/whole breast reference volume must be </= 30% based on the postoperative/pre-randomization CT scan.
9) Patients are eligible if, based on the postoperative/pre-randomization CT scan, PBI is judged to be technically deliverable by a technique for which the radiation oncology facility has been credentialed.
10) Patients with a history of non-breast malignancies are eligible if they have been disease-free for 5 or more years prior to randomization and are deemed by their physician to be at low risk for recurrence. Patients with the following cancers are eligible if diagnosed and treated within the past 5 years: carcinoma in situ of the cervix, carcinoma in situ of the colon, melanoma in situ, and basal cell and squamous cell carcinoma of the skin.
11) Patients must be >/= 18 years old.