[Factors affecting the contralateral dose for the non-treated breast in irradiation following quadrantectomy]

We evaluated, with a treatment planning system, the maximum and the mean contralateral breast doses, and, with thermoluminescent dosemeters LiF100; the skin dose during radiation therapy after conservative surgery. The doses were correlated with technical parameters through statistical analysis. Since 1995, 100 patients have been considered, all of them treated with two 60Co tangential beams after quadrantectomy. The mean dose to the contralateral breast exhibited a statistically significant correlation with the gantry angle of the lateral (Pearson, p < .02) and medial beams (p < .01); the maximum dose was correlated with the gantry angle of the lateral (p < .002) and the medial beams (p < .002). In the last 50 patients, the skin dose (measured with TLDs) was correlated with: distance from beam edge (Pearson, p < .02), breast thickness (p < .01), gantry angle of the lateral beam (p < .005), gantry angle of the medial beam (p < .002). Furthermore, only the gantry angle of the lateral (p < .02) and of the medial beams (p < .01) exhibited statistically significant Spearman's correlation with skin dose. Wilcoxon's signed rank sum test for paired data was performed to study wedge dependence. The average contralateral breast dose using two wedges was statistically reduced with respect to the dose without wedges (p < .02). These results suggest that the dose to the contralateral breast could be significantly decreased by careful attention to the treatment details, which implies that the procedures related to the technical aspects of the therapy should be submitted to careful quality control.