Utility of three-dimensional planning for axillary node coverage with breast-conserving radiation therapy: Early experience

PURPOSE:To examine the dosimetric axillary nodal coverage with standard tan gential breast radiation fields and determine the utility of three-dimensio nal treatment planning for such coverage. MATERIALS AND METHODS: Six consecutive patients who were to undergo whole-b reast irradiation underwent computed tomographic scanning with 5-mm section s at the time of treatment simulation. Contours were made with a commercial workstation for the lower axillary tissues, lungs, and heart. Axillary cov erage was examined with three-dimensional isodose visualization and dose-vo lume histograms for four plans for each patient: (a) standard tangential ra diation fields designed to cover only the breast, with clinical setup; (6) standard tangential fields with beam's-eye-view optimization of collimator angles for axillary and breast coverage; (c) standard tangential fields wit h adjustment of field width and collimator angles; and (d) customized field s, by adjusting width,collimator angle, and gantry angle and by using custo mized blocks. RESULTS: With plan a, only one patient had a simulated mean axillary dose g reater than 90% of that prescribed. Underdosing occurred primarily in the p osterior superior axillary nodal region. Plan b improved axillary coverage; five patients had a simulated mean axillary dose of 89% or more of the pre scribed dose, with adequate whole-breast coverage and no increased pulmonar y or cardiac doses. Adjusting the field width and gantry angle further impr oved simulated mean axillary doses; however, customized blocking was then r equired to avoid increased mean pulmonary and cardiac doses and-unacceptabl e contralateral breast doses. CONCLUSION: When coverage of lower axillary nodal tissue is desired at brea st irradiation, three-dimensional planning with beam's-eye-view adjustment of tangential fields should be considered.