Dosimetric comparison of three different external beam whole breast irradiation techniques

Introduction: The purpose of this study was to compare the dosimetries of three different external beam whole breast radiotherapy techniques: two-dimensional RT (2D-RT), three-dimensional conformal RT (3D-CRT), and field-in-field intensity-modulated RT (FiF-IMRT). In addition, we aimed to evaluate the patients who needed more or less complex treatment modalities. Methods: Thirty patients were included in the study. All the patients had earlystage breast cancer and conserving surgery had been performed. Plans that employed the three techniques were generated for each patient. Dosimetric comparisons were conducted, and correlations with patient characteristics and dosimetric outcomes were analyzed. Results: The 2D-RT technique was found to be suboptimal for treating the intact breast. Its dose homogeneity index (DHI) was 20.68. The authors were unable to define a patient characteristic in which 2D-RT dosimetry would perform better. FiF-IMRT was found to be the superior technique with a better homogeneity in the breast (DHI=9.35 and P=0.000002 when compared to 3D-CRT). When compared according to patient characteristics, again the FiF-IMRT planning is the best for all subgroups, but the DHI gets worse by increased breast volume and separation. While FiF-IMRT achieves better DHI in the breast, it has little effect on heart and lung doses. But the normal tissues' volume (cc) that gets the 100% of the prescribed dose (V100) was lowered because of the treatment without wedges and scatter and with less monitor unit. Conclusions: 2D-RT could not be performed safely on the intact breast in any of the subgroups. FiF-IMRT is a superior technique for breast dosimetry, and normal tissue. For patients with large breast size or separation, further intensive techniques must be investigated.