Accurate targeting of treatment sites should increase local control by radiation therapy for breast-cancer lumpectomy patients. Currently, ultrasound localization is used for prostate cancer patients to locate the prostate before daily radiation treatments. There is now documented evidence that the lumpectomy site does change during the external radiation therapy. Thus, treatment efficacy should be increased by localizing the target, monitoring volume changes, and adjusting the radiation target prior to the boost radiation dose.

Study participants will have weekly ultrasounds performed of the lumpectomy cavity to determine shift and volume changed from the initial treatment-planning CT to the time of the radiation boost (approximately 4 weeks). These ultrasounds are done prior to their weekly doctor's appointment with Radiation Oncology.

When it is time to perform the radiation boost (when the radiation is more targeted to the lumpectomy cavity), the ultrasound will be done daily with the participant in treatment position. The SonArray system used for the ultrasound-driven targeting for prostate cancer will be utilized. If the lumpectomy cavity is observed, the ultrasound suggested shifts will be noted and compared to the shifts needed for standard clinical set up.

Once the subject has completed radiation therapy, the study participation is complete.

Inclusion Criteria:

• Ability to understand and the willingness to sign a written informed consent document.
• Patients must have histologically or cytologically confirmed breast carcinoma with voluntarily elected breast conservation techniques (i.e., lumpectomy)
• Age >18 years. Breast cancer, while not restricted only to adult women, is rare in the younger population.
• Radiation indicated as a post-surgical adjuvant treatment for breast conservation.
• Life expectancy of greater than 6 months.
• Karnofsky of greater or equal to 60
• The effects of radiation therapy on the developing human fetus at the recommended therapeutic dose can be abortifacient. For this reason, and because radiation therapy is known to be teratogenic, women of child-bearing potential and men must agree to use adequate contraception (hormonal or barrier method of birth control; abstinence) prior to study entry and for the duration of study participation. Should a woman become pregnant or suspect she is pregnant while participating in this study, she should inform her treating physician immediately.

Exclusion Criteria:

• Patients who have not recovered from adverse events due to agents administered more than 4 weeks earlier.
• The inability to visualize or reliably contour the lumpectomy cavity from the Radiation Oncology treatment planning CT scan.
• Patients with known brain metastases should be excluded from this clinical trial because of their poor prognosis and because they often develop progressive neurologic dysfunction that would confound the evaluation of neurologic and other adverse events.
• Uncontrolled intercurrent illness including, but not limited to, ongoing or active infection, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or psychiatric illness/social situations that would limit compliance with study requirements in the opinion of the principal investigator.
• Pregnant women are excluded from this study because radiation therapy has the potential for teratogenic or abortifacient effects. Because there is an unknown but potential risk for adverse events in nursing infants secondary to treatment of the mother with standard chemotherapeutic regimens (if applicable), breastfeeding should be discontinued if the mother is treated any adjuvant chemotherapy.

Women and men who have had lumpectomy for the definitive treatment of breast cancer and have a defined cavity from this procedure.