Three-field breast irradiation technique using tangential quarter fields.

We have developed and implemented in clinical practice an isocentric three-field breast irradiation technique using tangential quarter fields. In this technique, the same isocenter is used for the supraclavicular and the tangential breast fields. The superior-posterior corner of the tangential breast fields is placed at the central axis by asymmetric collimation of both the length and the width of the field. Consequently, the beam divergence at both the superior and posterior edges is eliminated, allowing a perfect geometric match between the posterior borders of both tangential breast fields and the supraclavicular field without table rotation. Compared to conventional techniques requiring table rotations, the present method produces a more uniform dose distribution in the target volume and requires significantly less simulation time.