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Breast-conserving radiation therapy: potential of inverse planning with intensity modulation
M C Smitt1, S D Li, C A Shostak
1Department of Radiation Oncology, Stanford University Medical Center, CA 94305, USA.
Purpose:
To evaluate inverse planning with beam-intensity modulation in breast-conserving radiation therapy.
Materials And Methods:
A prototype inverse treatment-planning system was used in five patients with early-stage breast tumors. The prescription for the breast was 5,040 cGy in 180-cGy fractions, with the primary tumor site receiving 6,000 cGy in 214-cGy fractions. Isodose distributions from the prototype were compared section by section with those from conventional three-dimensional planning.
Results:
The inverse planning system showed dose variation of 84%-98% to 111%-113% in the primary tumor site. For whole-breast irradiation, 95% of the target volume received at least 4,000 cGy. High-dose areas were adjacent to the primary site. Lower-dose areas were in the most medial part of the breast. Compared with the conventional system, target doses were similar. The volume of lung and heart that received high doses was smaller; however, larger lung and heart volumes received doses of less than 1,200 cGy.
Conclusion:
Intensity modulation may accomplish "concomitant boost" treatment. Acceptable dose gradients are achieved in the target volumes, with lower volumes of high-dose treatment in normal tissue. Plans that required comprehensive nodal radiation, in particular, were improved relative to conventional plans. Optimization of the planning system is needed to minimize the lung and heart volumes that receive low-dose radiation.