A simple isocentric technique for irradiation of the breast, chest wall and peripheral lymphatics

The major problem with the standard technique for irradiation of the breast or chest wall and peripheral lymphatics is field matching at the junction between the supraclavicular and tangential fields. Overdosing or under-dosing across the junctions is unavoidable because of beam divergence. Various techniques using a half-blocked supraclavicular field in conjunction with special tangential fields have been introduced recently to eliminate the junction problem; they are, however, complicated, involving couch motions and machine isocentre repositioning when changing from the supraclavicular to the tangential fields. The breast treatment technique which we have used over the past twelve months utilises a supraclavicular half-blocked field, two tangential half-blocked fields and an optional posterior axillary field. The technique is simple and easy to set up since the same machine isocentre is used for all treatment fields and no couch movement or patient repositioning is required. The same half-block collimator which is used to define the caudad border of the supraclavicular field is used to define the cephalad edges of the two tangential fields. The margin of error of treatment is reduced and the dose measurements demonstrate excellent dose homogeneity through the entire treatment volume with no overdose or underdose at the field junction.