RTOG 0413 volumes of interest. The balloon, PTV_EVAL, ipsilateral breast, and air volumes are depicted. The balloon is contoured at the edge of the contrast medium. PTV_EVAL is a 1‐cm expansion from the balloon surface, excluding the balloon volume, the chest wall and pectoralis muscle, and the first 5 mm inside the skin surface. Air pockets inside the treatment volume are contoured, but air pockets within the balloon are not included. The ipsilateral breast is contoured as are all tissues within the standard tangential field borders, except the lung.