BACKGROUND AND PURPOSE: Radiotherapy can induce tissue reactions with an edema leading to increased breast volume. The aim of the present study was to quantify this increase and analyze its effect on the electron boost technique. PATIENTS AND METHODS: 140 patients with breast cancer treated with breast-conserving surgery underwent CT planning before, during and/or after radiotherapy in order to evaluate breast volume changes due to radiotherapy. CT data were analyzed using the HELAX planning system and dose distribution was assessed. Determination of the breast volume was achieved using an interpolation algorithm. Three subgroups were analyzed: group 1 (n = 47): < or = 670 cm(3), group 2 (n = 46): 671-999 cm(3), and group 3 (n = 47): > or = 1000 cm(3) breast volume. RESULTS: The mean initial breast volume was 907 cm(3) (100-3073 cm(3)). After radiotherapy, mean breast volume increased by 81 cm(3) to 988 cm(3) (109-3185 cm(3)). Significant changes in volume were observed after a dose of 40 Gy. According to the subgroups mean volume increase was as follows: group 1: 53 cm(3) (3-120 cm(3)), group 2: 85 cm(3) (20-200 cm(3)), and group 3: 105 cm(3) (5-340 cm(3)). This difference was statistically significant for all subgroups (p < 0.001). Corresponding to the volume increase, depth of the boost target volume changed up to 1.0 cm. CONCLUSION: As radiotherapy may lead to a significant increase in breast volume, it seems appropriate to perform a second planning CT after about 40 Gy in order to optimize dose distribution for boost irradiation.
BACKGROUND AND PURPOSE: Radiotherapy can induce tissue reactions with an edema leading to increased breast volume. The aim of the present study was to quantify this increase and analyze its effect on the electron boost technique. PATIENTS AND METHODS: 140 patients with breast cancer treated with breast-conserving surgery underwent CT planning before, during and/or after radiotherapy in order to evaluate breast volume changes due to radiotherapy. CT data were analyzed using the HELAX planning system and dose distribution was assessed. Determination of the breast volume was achieved using an interpolation algorithm. Three subgroups were analyzed: group 1 (n = 47): < or = 670 cm(3), group 2 (n = 46): 671-999 cm(3), and group 3 (n = 47): > or = 1000 cm(3) breast volume. RESULTS: The mean initial breast volume was 907 cm(3) (100-3073 cm(3)). After radiotherapy, mean breast volume increased by 81 cm(3) to 988 cm(3) (109-3185 cm(3)). Significant changes in volume were observed after a dose of 40 Gy. According to the subgroups mean volume increase was as follows: group 1: 53 cm(3) (3-120 cm(3)), group 2: 85 cm(3) (20-200 cm(3)), and group 3: 105 cm(3) (5-340 cm(3)). This difference was statistically significant for all subgroups (p < 0.001). Corresponding to the volume increase, depth of the boost target volume changed up to 1.0 cm. CONCLUSION: As radiotherapy may lead to a significant increase in breast volume, it seems appropriate to perform a second planning CT after about 40 Gy in order to optimize dose distribution for boost irradiation.