Breast cancer remains the most common type of cancer in women with over 200,000 cases diagnosed per year in the United States alone. When breast cancers are discovered at an early, "localized" stage and treated appropriately there is a 97% rate of five-year survival. The current standard of treatment for early-stage breast cancer is lumpectomy followed by radiation.

Breast conservation therapy (BCT) consists of a lumpectomy and whole-breast external-beam radiation therapy (WB-EBRT), which is usually delivered in a period of 5-6 weeks. This is an accepted and appropriate local treatment option for selected patients with early-stage breast cancer instead of surgically removing the breast (mastectomy).

Recently, new technologies have allowed for more attractive treatment options for the treatment of early stage breast cancer. Brachytherapy for example, uses high dose remote control radiation and is a highly desirable method to treat breast cancer patients.

The most common reasons for this are advanced age and/or difficulty with travel for daily treatment for 6 weeks. This has sparked interest in other treatment options such as accelerated partial breast irradiation (APBI) which uses brachytherapy to allow the delivery of more focused RT over a shorter period of time. APBI is superior to whole-breast external-beam radiation therapy (WB-EBRT) in two ways:
1. Radiation only targets the segment surrounding the tumor rather than the whole breast.
2. Radiation is delivered in fewer fractions at larger doses so that total treatment time is only 5 to 7 days.

The mammosite applicator consists of a double-lumen balloon catheter with a balloon similar to that of a Foley catheter, which is inflated once the catheter is inserted within the lumpectomy cavity.

During treatment, a computer controlled afterloader brachytherapy unit feeds a single radioactive source into the balloon. Once it has emitted the prescribed dose of radiation, the source is removed. After 10 sessions in five to seven days, the balloon is deflated, and the catheter is removed.

MammoSite delivers radiation to the area where it is needed most with minimal radiation exposure to healthy tissue reducing the potential for side effects.

Good to excellent cosmetic results are seen in most patients. The advantage of the shorter treatment time is especially helpful for patients who live far away from a center of radiation therapy. Older women are excellent candidates for this treatment as well because patients are treated on an outpatient basis. Finally, breast brachytherapy has the advantage that in patients who need a combination treatment with chemotherapy, the cancer drugs can be given immediately after the brachytherapy procedure causing no delay to the systemic treatment.