Three-field isocentric breast irradiation using asymmetric jaws and a tilt board.

Perfect abutment of medial and lateral tangential breast portals with the adjacent supraclavicular field may be achieved with ease. A simple and safe approach was developed using a tilt board and new technology that is standard on a popular linear accelerator. The patient is secured on a tilt board as a means to level the chest wall. Isocenter is placed at depth on the matchline, where asymmetric jaws are used to produce non-divergent field edges and a perfect abutment. This is done without the need for table or collimator rotations, beam-splitters, or vertical cephalad blocks. The dorsal beam edge of the tangents is made coplanar by rotating the gantry more than 180 degrees. This procedure produces a dosimetrically sharp field edge and eliminates concern about block transmission and excess dose to the contralateral breast. Set-up is fast, and the steps involved are simple and few. Advantages and limitations of this technique are presented.