The purpose of this study is to determine if an alternative imaging protocol done at the time of radiotherapy treatments for patients with breast cancer can improve accuracy in patient set-up.

Accurate patient positioning is critical in Radiation Therapy. Electronic imaging is used to compare a patient's actual treatment position, with that which was planned from an initial CT scan. Radiation Therapists compare planned and actual images using analysis software to determine if differences are within acceptable tolerances. At the VIC, we use 3 different breast imaging protocols depending on the patient set-up and treatment technique. Findings from our recent retrospective planning study show that our current electronic imaging protocols miss some clinically significant patient set-up errors, particularly in the medial/lateral direction, and that these errors can be better detected with the use of an anterior image. The purpose of this study is to test these findings prospectively in clinical practice, through the direct comparison of our current protocols with a proposed new protocol, which would include an anterior electronic portal image (EPI).

Inclusion Criteria:

• All patients (male or female) receiving tangential breast/chest wall radiotherapy only, or three or four field breast/chest wall and nodal radiotherapy will be eligible.

Exclusion Criteria:

• Those patients receiving partial breast treatment, those patients requiring an electron match field, those on another breast cancer radiotherapy trial, those who require radiotherapy using deep inspiration breath hold or multi-field intensity modulated radiotherapy, and all non-breast cancer patients will be excluded.