Three-field isocentric technique for breast irradiation using individualized shielding blocks.

The three-field technique is the most common method used for breast and regional node treatment after conservative surgery. Several variants of this technique, which are characterized by complex geometrical problems, have been described. A possible simplification of this technique and the use of individualized shielding blocks both for anterior and for tangential fields is proposed, thus allowing for the simultaneous shielding of the half beam and the critical areas. Advantages of isocentrical techniques are thereby maintained, but the number of mechanical movements required is minimized and collimators and couch rotations are not needed. Patient set-up time is also greatly shortened. The accuracy of this technique has been verified using both photographic methods and thermoluminescent dosimetry.