Post-operative (lumpectomy or mastectomy) female breast cancer patients who will receive radiation to the whole breast or chest wall and the regional nodes.

ARM uses dye to track lymphatic flow of the upper extremities.We hypothesize that iodinated contrast injected into the upper inner arm (same site that surgeons inject during ARM) 15 minutes before the time of CT simulation will similarly be able to track the UELs. We will contour the visible iodinated dye and will measure if that anatomically correlates with the general known location of the UELs. Two radiation oncologists will independently determine if they can delineate the UELs. If both radiation oncologists can identify and contour the UELs in a reproducible fashion, we will code the patient as "UEL identified." If one or both physicians are either not able to identify the UEL on CT images or the contoured UEL structures are significantly different from each other, we will code the patient as "UEL not identified."

We will measure the Dmax, Dmin, Dmean, D25%, and D75%. Dmax is the maximum dose (in units of Gray) delivered to the UEL, while Dmin is the minimum dose and Dmean is the mean dose. D25% and D75% are the minimum dose delivered to 25% and 75% of the UEL, respectively. We will also look at the percent of theoretical radiation plans that could be safely modified. This will be a binary outcome: either the plan can be modified safely, or it cannot.