Intensity-modulated radiotherapy technique for three-field breast treatment

Purpose: To develop a simplified intensity-modulated radiotherapy (IMRT) algorithm for three-field breast treatment using a single isocenter setup. The algorithm aims to deliver a uniform dose throughout the breast volume. Special attention was paid to the highly divergent nature of the beam configuration. Methods and Materials: Computed tomography (CT) image setup of the patient was acquired. On each CT slice, the computer automatically generated lines parallel to the posterior edge of the tangent field. The mid-point of each line segment that intersected the breast was determined and the dose from an open field calculated. The intensity of the divergent pencil beam corresponding to the mid-point was set to be inversely proportional to the open field dose to the mid-point. Forward dose calculation was then performed using this intensity distribution. Results: A total of 15 breast cancer patients undergoing three-field IMRT who underwent planning and treatment with this algorithm were included in this study. Compared with standard wedged pair tangents, the IPIRT plan produced statistically significant better dose distributions in terms of target coverage and target dose uniformity, as well as reduced dose to the contralateral breast and reduced hot spots to the ipsilateral lung. Conclusion: Since March 2004, the new IMRT algorithm has been used for planning and treatment of > 20 patients undergoing three-field treatment, as well as > 200 patients undergoing regular two-field tangent treatment, all with excellent dose distributions throughout the breast volume. (c) 2005 Elsevier Inc.