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[Radiation injury of the lung following postoperative radiotherapy of breast cancer using a single large portal technique--CT study].

When postoperative radiotherapy for breast cancer is indicated, we employ a single large portal technique with electron beams using a bolus made of MIX-R (soft tissue equivalent material) for the chest wall. The entire lymph node groups as well as the chest wall are irradiated uniformly, and the total dose is 50 Gy, 2 Gy/fraction, 5 days/week. Radiation changes of the lung in 35 breast cancer patients irradiated by this technique were evaluated by computed tomographic (CT) studies. Radiation injuries were detected in 12 patients out of 35 (34%). Among patients who were irradiated by three portal techniques without bolus, radiation injuries were detected in all 4 patients (100%) by CT and in 39 patients out 72 (54%: historical control group) by plain chest film. These results indicated the superiority of the single large portal technique. Radiation injuries were identified in CT studies at 135 day after commencement of radiotherapy, and their distributions were localized to areas of 80-100% dose level. Measurements in CT revealed that the thickness of the chest wall varied extremely according to surgical procedures, so that the adequacy of the selection of energy of electron beams in each patient by CT was indispensable.