4D Image-Guided Partial Breast Radiation in Stage 0 and l Breast Cancer

Inclusion Criteria:

* The patient must consent to be in the study and must have a signed an approved consent form conforming with institutional guidelines.
* Patient must be \> 50 years old.
* The patient should have a life expectancy of at least two years with a karnofsky performance status \> 70.
* The patient must have stage 0 or I breast cancer.
* On histological examination, the tumor must be DCIS or invasive adenocarcinoma of the breast.
* Surgical treatment of the breast must have been lumpectomy. The margins of the resected specimen must be histologically free of tumor (\>2mm, DCIS and invasive). Re-excision of surgical margins is permitted.
* Gross disease must be unifocal with pathologic (invasive and/or DCIS) tumor size 2 cm or less. (Patients with microscopic multifocality are eligible as long as total pathologic tumor size is 2 cm or less.)
* Patients with invasive breast cancer are required to have axillary staging which can include sentinel node biopsy alone (if negative), sentinel node biopsy followed by axillary dissection or sampling with a minimum total of 6 axillary nodes or axillary dissection alone (with a minimum of 6 axillary nodes). Axillary staging is NOT required for patients with DCIS.
* The patient must have simulation within 8 weeks/56 days of the final surgery for their breast cancer (lumpectomy, re-excision of margins, or axillary staging procedure).
* Patients with a history of non-ipsilateral breast malignancies are eligible if they have been disease-free for 2 or more years prior to enrollment. Patients with the following cancers are eligible even if diagnosed and treated within the past 2 years: carcinoma in situ of the cervix, colon, melanoma in situ, and basal cell and squamous cell carcinoma of the skin.
* Chemotherapy is permitted if planned for ≥ 2 weeks after radiation.
* Urine pregnancy test must be performed and be negative on all women younger than 60 who have not had a tubal ligation, oophorectomy, or hysterectomy.
* Separate incisions for the lumpectomy and sentinel node biopsy should be present. Use of only one incision will typically result in a contiguous cavity with the tumor bed and the sentinel node sampling, and inability of the radiation oncologist to delineate the tumor bed from the sentinel node bed.
* The patient must have a cavity which is able to be targeted with external beam APBI, either through surgical clip placement, or CVS 3 or higher. The cavity to whole breast ratio must be 30% or less.

Exclusion Criteria:

* Men are not eligible for this study as men are not breast conservation candidates.
* T0, T2 (\> 2.0 cm), T3, node positive, stage III or IV breast cancer.
* Any positive axillary nodes.
* Palpable or radiographically suspicious ipsilateral or contralateral axillary, supraclavicular, infraclavicular or internal mammary nodes, unless biopsy proven to be negative for tumor.
* Suspicious microcalcifications, densities or palpable abnormalities in either breast unless biopsy proven to be benign.
* Non-epithelial breast malignancies such as sarcoma or lymphoma.
* Proven multicentric carcinoma in more than one quadrant or separated by more than 2 centimeters.
* Paget's disease of the nipple.
* History of invasive breast cancer or DCIS in the same breast.
* Surgical margins that cannot be microscopically assessed or are less then 2 mm.
* Collagen vascular disease, specifically dermatomyositis with a CPK level above normal or with an active skin rash, systemic lupus erythematosis or scleroderma.
* Pregnancy or lactation at the time of proposed radiation. Women of reproductive potential must agree to use an effective non-hormonal method of contraception during therapy.
* Psychiatric or addictive disorders or other conditions that, in the opinion of the treating physician, would preclude the patient from meeting the study requirements.
* Patients with coexisting medical conditions in whom life expectancy is \< 2 years.
* Patients with skin involvement, regardless of tumor size.