Pilot study of feasibility and dosimetric comparison of prone versus supine breast radiotherapy

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. 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. 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. 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.