External partial-breast radiation is a method of therapy that zeroes in on the area around where the cancer was, minimizing or avoiding radiation to most of the remaining breast tissue.
The thought behind external partial-breast radiation is to treat only the area of the breast that is at highest risk of recurrence. The risk of cancer coming back in a different part of the same breast is quite low.
Only a few very small studies with very little follow-up have been done on giving partial-breast radiation externally after surgery. (Most partial-breast radiation techniques are considered internal radiation.) Researchers are studying partial-breast external radiation for use after lumpectomy to see how the benefits compare to the current standard of radiation to the whole breast.
External beam partial-breast radiation starts with a planning session (simulation). A special CAT scan of the breast is done and is used to map out small treatment fields for the area at risk. The type and distribution of radiation is designed to maximize the dose to the area that needs to be treated and avoid or minimize radiation to tissue near the area. The radiation is delivered with a linear accelerator, the same machine used in regular external radiation, twice a day for 1 week.