RESUMEN
PURPOSE: The aim of this study was to demonstrate feasibility and analyze dosimetric differences in prone and supine position breast cancer radiotherapy in women with large or pendulous breast. METHODS: Ten post-lumpectomy breast cancer patients underwent supine and prone computed tomography-based treatment plan. On each data set, the whole breast, the ipsilateral lung and the heart were outlined. Multisegment tangential-fields plans were generated for each position. Target coverage, homogeneity, overdosage outside breast and organ at risk sparing were analyzed and compared for supine and prone position. RESULTS: Coverage and dose homogeneity of the PTV measured by D 90 and V(95)% were similar for both plans although breast maximum dose was higher in the supine plan (p = 0.017). Prone position reduced the percentage of ipsilateral lung receiving 20 Gy (V(20Gy)) from 26.5 to 2.9 % (p = 0.007), medium lung dose, as well as the percentage of the heart receiving 35 Gy heart (V(35Gy)) from 3.4 to 1.2 % (p = 0.038). Overdosage of areas outside breast PTV was also consistently reduced with prone position (p = 0.012). In addition, average number of segments and monitor units needed was reduced in prone position. CONCLUSIONS: Prone position in large breast women appears to favor normal tissue sparing in breast radiotherapy as compared to supine position, without diminishing the target coverage.