A single isocenter three-field breast irradiation technique using an empiric simulation and asymmetric collimator

The treatment of abutting fields presents multiple difficulties, including problems of field overlaps or gaps, complexity of simulation, and the difficulties of daily setup and variation. Multiple techniques have been described for the treatment of the breast/chest wall and supraclavicular nodes using tangents and a matched supraclavicular field. The techniques described have used collimator angles, couch angles, and/or corner blocks in an attempt to match these fields with no overlap or gap. Some of these techniques required complex calculations or treatment devices to achieve a geometric match between fields. We describe a technique for treatment of breast and supraclavicular nodes that uses a single isocenter and requires asymmetric collimator jaws to give half-blocked fields. The simulation and setup are done empirically, with no complex calculations required. The daily setup and treatment can be done rapidly and reliably, with no extra equipment required. Custom blocks may be used to conform to the chest wall contour and decrease the amount of lung in the treatment fields.