Use of segmental boost fields in the irradiation of inguinal lymphatic nodes

En face electron fields to boost inguinal lymphatics have been used by oncologists for many years. With the introduction of multileaf collimators (MLC) and independent jaws, the practice of creating segmental fields to boost areas of interest has expanded. Typical anterior-posterior opposing field treatment of the pelvis may now be enhanced to include additional anterior segments to boost lymphatic tissue at a predetermined depth. This report illustrates the clinical implementation of one such segmental boost technique. Computer generated isodose plans utilize manual contour and CT-generated data for analysis of inguinal lymphatic depths. Potential areas of field overlap are discussed as well as the use of combined 6 and 15 MV photon energies to reduce areas of inhomogeneous dose. Technical details associated with MLC field size limits and other clinical factors are also discussed in relationship to smooth treatment delivery.