Purpose: A method that uses electronic portal imaging to design intensity-modulated beams for compensation in breast radiotherapy was implemented using 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 tomography (CT) and on a treatment unit using an electronic portal imager. The portal imaging data were used to design intensity-modulated beams to give an ideal dose distribution in the breast. These beams were implemented as multiple static fields added to standard wedged tangential fields. Planning of these treatments was performed on a commercial treatment planning system (Target 2, IGE Medical Systems, Slough, U.K.) using the CT data for each patient. Dose-volume histogram (DVH) analysis of the plans with and without multileaf collimator (MLC) compensation was carried out. This work has been used as the basis for a randomized clinical trial investigating whether improvements in dosimetry are correlated with the reduction of long-term side effects from breast radiotherapy.
Results: The planning analysis showed a mean increase in target volume receiving 95-105% of prescribed dose of 7.5% (range -0.8% to 15.9%) when additional MLC compensation was applied. There was no change to the minimum dose for all 14 patient data sets. The change in the volume of breast tissue receiving over 105% of prescribed dose, when applying MLC compensation, was between -1.4% and 11.9%, with positive numbers indicating an improvement. These 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 using an electronic portal imager has been verified using planning on CT data for 14 patients. An improvement was seen in planning when applying MLC compensation and this effect was greater the larger the breast size.