Dosimetric improvements following 3D planning of tangential breast irradiation

Purpose: To evaluate the dosimetric difference between a simple radiation t herapy plan utilizing a single contour and a more complex three-dimensional (3D) plan utilizing multiple contours, lung inhomogeneity correction, and dose-based compensators. Methods and Materials: This is a study of the radiation therapy (RT) plans of 85 patients with early breast cancer. All patients were considered for b reast-conserving management and treated by conventional tangential fields t echnique. Two plans were generated for each patient. The first RT plan was based on a single contour taken at the central axis and utilized two wedges . The second RT plan was generated by using the 3D planning system to desig n dose based compensators after lung inhomogeneity correction had been made . The endpoints of the study were the comparison between the volumes receiv ing greater than 105% and greater than 110% of the reference dose, as well as the magnitude of the treated volume maximum dose. Dosimetric improvement was defined to be of significant value if the volume receiving > 105% of o ne plan was reduced by at least 50%,vith the absolute difference between th e volumes being 5% or greater. The dosimetric improvements in 49 3D plans ( 58%) were considered of significant value. patients' field separation and b reast size did not predict the magnitude of improvement in dosimetry. Conclusion: Dose-based compensator plans significantly reduced the volumes receiving > 105%, >110%, and volume maximum dose. (C) 2000 Elsevier Science Inc.