Aria 15

All patients were planned using External Beam Application in ARIA 15.6 (Varian Medical Systems, Palo Alto, California, USA) using a hybrid IMRT technique.²³ This technique involves treating the patient with open tangential fields followed by IMRT tangential fields. The open fields are those static fields delivered without MLCs, defined by setting the jaws according to anatomical landmarks of clinical interest. Additional MLC shielding can be added to the open fields to shield the heart or to shield part of the lung when the collimator is set to zero degrees (for patients receiving supraclavicular irradiation). The jaws of the IMRT fields are set to the same size as the static fields, and the plan is optimized to deliver a uniform dose throughout the breast, typically resulting in a smooth sweep of MLCs. The static fields delivered between 50% and 80% of the dose, and these are the fields where EPID images were acquired and the position of the chest wall was identified. This was only done for the static fields since the sweeping MLCs of the IMRT fields will eventually block the chest wall.