Evaluation of compensation in breast radiotherapy: A planning study using multiple static fields

Purpose: A method that uses electronic portal imaging to design intensity-m odulated beams for compensation in breast radiotherapy was implemented usin g multiple static fields in a planning study, We present the results of the study to verify the algorithm, and to assess improvements to the dosimetry , Methods and Materials: Fourteen patients were imaged with computed tomograp hy (CT) and on a treatment unit using an electronic portal imager, The port al imaging data were used to design intensity-modulated beams to give an id eal dose distribution in the breast. These beams were implemented as multip le static fields added to standard wedged tangential fields. Planning of th ese treatments was performed on a commercial treatment planning system (Tar get 2, IGE Medical Systems, Slough, U.K.) using the CT data for each patien t. Dose-volume histogram (DVH) analysis of the plans with and without multi leaf collimator (MLC) compensation was carried out. This work has been used as the basis for a randomized clinical trial investigating whether improve ments in dosimetry are correlated with the reduction of long-term side effe cts from breast radiotherapy. Results: The planning analysis showed a mean increase in target volume rece iving 95-105% of prescribed dose of 7.5% (range -0.8% to 15.9%) when additi onal MLC compensation was applied, There,vas no change to the minimum dose for all 14 patient data sets, The change in the volume of breast tissue rec eiving over 105% of prescribed dose, when applying MLC compensation, was be tween -1.4% and 11.9%, with positive numbers indicating an improvement, The se effects showed a correlation with breast size; the larger the breast the greater the amount of improvement, Conclusions: The method for designing compensation for breast treatments us ing an electronic portal imager has been verified using planning on CT data for 14 patients. An improvement was seen in planning when applying MLC com pensation and this effect was greater the larger the breast size. (C) 2000 Elsevier Science Inc.