Three-field technique for breast irradiation using tangential field corner blocks.

A further modification of the three-field technique for the radiotherapy of the breast has been developed. Two isocentric opposing tangential fields encompass the breast, chest wall, and may include the internal mammary lymph nodes. The third, an anterior field, encompasses the axilla and supraclavicular areas. As with our previously reported techniques, the objectives of the present modification is to make the posterior edges of the tangential fields coplanar and to match the cephalad geometric edges of the tangential fields to the caudad geometric edge of the supraclavicular field. A half-beam block is used to shield the caudad half of the anterior field, thus producing a vertical transverse plane to which the tangential fields are matched. Small corner blocks are used on the cephalad edges of the tangential fields to produce the vertical edge necessary for matching to the anterior field. It is essential that the match between the tangential fields and the anterior field be geometrically correct to ensure both local control of disease and good cosmetic results. Two advantages of the present technique are the ease with which it can be carried out and the precision of the match plane without the use of cumbersome mechanical accessories.