Development of Highly Accurate Radiotherapy System for Breast Conservation Therapy for Breast Cancer

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1.In 1995, we started place metal clips along the resection margin during breast conserving surgery. In CT-Simulation (CT-S), these metal clips were identified on the CT image and the boost irradiation field was automatically generated around the clips. This method enabled more accurate set-up of the boost irradiation field than conventional method. However, the size of the boost radiation field thus generated was approximately 50% larger than those based on conventional method. To address this issue, We started to correlate the pathological information with individual clip.2.In a series of 20 patients, we compared the 3-D dose distribution between the plans created with CT-S and those created conventionally with surface anatomical markers. For posterolateral margin of the tangential beam, if mid-axillary line was used or posterior axillary line was used with head rotation of the gantry, significant part of the breast tissue escaped from the radiation field. The technique using posterior axillary line as a reference with head rotation of the gantry resulted in the comparable coverage of the breast tissue., CT-S was, however, superior in that it generated more individualized plan for each patient.3.In a series of 24 patients, we compared the 3-D dose distribution between the two plans with same dimensions but different radiation source (60Co-gamma ray and 6 MV photon). In patients with large breast (<greater than or equal>400 cm3) or long separation, which was defined as the distance between the anteromedial and posterolateral margin at the isocenter plane, homogeneity of the dose distribution was significantly worse if 60Co-gamma ray was used. These results provided a guideline for an appropriate selection of radiatio