Intensity-modulated tangential beam irradiation of the intact breast

Purpose: To evaluate the potential benefits of intensity modulated tangenti al beams in the irradiation of the intact breast. Methods and Materials: Three-dimensional treatment planning was performed o n five left and five right breasts using standard wedged and intensity modu lated (IRI) tangential beams. Optimal beam parameters mere chosen using bea ms-eye-view display. For the standard plans, the optimal wedge angles were chosen based on dose distributions in the central plane calculated without inhomogeneity corrections, according to our standard protocol. Intensity-mo dulated plans were generated using an inverse planning algorithm and a stan dard set of target and critical structure optimization criteria. Plans were compared using multiple dose distributions and dose volume histograms for the planning target volume (PTV), ipsilateral lung, coronary arteries, and contralateral breast. Results: Significant improvements in the doses to critical structures were achieved using intensity modulation. Compared with a standard-wedged plan p rescribed to 46 Gy, the dose from the IM plan encompassing 20% of the coron ary artery region decreased by 25% (from 36 to 27 GS) for patients treated to the left breast; the mean dose to the contralateral breast decreased by 32% (from 1.2 to 0.7 Gy); the ipsilateral lung volume receiving more than 3 6 Gy decreased by 30% (from 10% to 7%); the volume of surrounding soft tiss ue receiving more than 46 Gy decreased by 31% (from 48% to 33%). Dose homog eneity within the target volume improved greatest in the superior and infer ior regions of the breast (approximately 8%), although some decrease in the medial and lateral high-dose regions (approximately 4%) was also observed. Conclusion: Intensity modulation with a standard tangential beam arrangemen t significantly reduces the dose to the coronary arteries, ipsilateral lung , contralateral breast, and surrounding soft tissues. Improvements in dose homogeneity throughout the target volume can also be achieved, particularly in the superior and inferior regions of the breast. It remains to be seen whether the dosimetric improvements achievable with IR-IRT will lead to sig nificant clinical outcome improvements. (C) 1999 Elsevier Science Inc.