Prone versus supine breast irradiation in early stage breast cancer patients.

Abstract

Abstract Abstract #5130 Introduction
 External beam radiotherapy for breast cancer patients is necessary after breast conserving therapy. Volume of breast tissue which needs to be irradiated is close to critical structures such as lung, heart; therefore an alternative prone position could be used to improve dose homogeneity during radiotherapy. The purpose of this study was to compare dose distribution within target and normal tissue volumes between two radiotherapy plans in prone and supine position in women with large and also with small breasts.
 Material and methods
 36 early breast cancer patients (15 – right side and 21 left side, 7 – small, 9 - median, and 20 – large breast size) in clinical stage T1-2N0 were treated with breast conserving therapy and were dedicated for further radiotherapy. Planning CT was performed in a prone and supine position and two treatment plans for each patient were developed using conventional tangents technique. Dose volume histograms were produced and plans were compared with regard to dose volumes parameters. Comparison of the different techniques was statistically analyzed using the Wilcoxon signed rank test.
 Results
 The mean doses to the target volume were (50.9 Gy ± 0.59 for supine position and 50.3 Gy ± 0.81 for prone position, p=0.005), minimum dose (39.9 Gy ± 3.7 vs. 38.7 Gy ± 7.7, p=0.6) and maximum dose (54.9 Gy ± 0.5 vs. 54.4 Gy ± 0.9, p=0.02), the dose in 95 % of PTV was significantly higher in supine compare to prone position (48.0 Gy ± 1.3 vs. 46.7 Gy ± 1.8, p=0.0002). The percentage of ipsilateral lung receiving specified dose were significantly higher in supine position compare to prone position: V5 Gy was 26.8% ± 9.5 for supine position and 7.7% ± 6.4 for prone position (p<0.0001), V10 Gy was 18% ± 7.9 vs. 4.8% ± 4.6 (p<0.0001) and V20 Gy was 12.1 ± 4.9 vs. 2.7% ± 2.8 (p=0.0001). Furthermore, the maximum and mean dose to the ipsilateral lung and heart was lower in prone position (max/mean lung 44.4/2.2 Gy, max/mean heart 27.9/2.4 Gy) compare to supine position (max/mean lung 51.4/7.8 Gy, max/mean heart 30.8/3.4 Gy).
 In the last part we precisely evaluated dose to the heart in left side breast patients. In this case there was significant decrease in maximum, mean and dose to the heart in prone position (max/mean heart 42.9/3.3 Gy, for prone position and max/mean heart 48.1/5 Gy for supine position). There was also smaller heart volume which received 5 Gy (10% ± 5.7 vs. 15.5 ± 11.1). Decrease in dose to the organ at risk was seen not only in large breast size patients but also in patients with smaller breasts.
 Conclusion
 Irradiation of patients in prone positions compare to supine positions did not improved dose distribution within target volume. Using plans generated in prone position we were able to reduce the dose to the organ at risk especially ipsilateral lung and heart. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 5130.