Room: AAPM ePoster Library
Purpose: To investigate the possibility of planning prone breast patients with wedges instead of open fields to eliminate the need for subfields covering the dose shadow cast by the breast board.
Methods: Tangents passing through a prone breast board were found to be attenuated by around 20% causing planners to utilize subfields to increase target coverage. Multiple prone breast patients who have been previously treated with open tangent fields were replanned with wedged fields. The quality of the new plans was compared to the originals, specifically focusing on maintaining coverage to the breast itself, and gaining coverage to the chest wall without the need of extra subfields to do so.
Results: From the visual plan comparisons and the averaged dose statistics across the plans, a claim can be made from the data that switching the plans to using wedged fields allows for deeper coverage without having to shoot large amounts of MUs specifically through the board. The coverage in the actual breast itself has worsened slightly in doing so, but that can be easily corrected and still should not require subfields for the breast board itself.
Conclusion: The improvement in coverage by switching to wedges indicates that prone breast plans can be made much more robust. When a subfield is needed specifically to increase dose to the chest wall, this can result in extreme over or under dosing if the patient is shifted even slightly on the day of treatment so that the beam is no longer shooting exactly through the breast board. This would not be an issue with a wedged field however, since a small shift in patient positioning would not result in as large of a dose discrepancy.