Acute and late side effects after intraoperative electron radiotherapy during breast conserving surgery of breast cancer.

1101 Background: Intraoperative boost irradiation as part of breast-conserving therapy is a perfect method to adequately capture the high risk tumor relapse area. The most homogeneous dose distribution is achieved with electrons. Intraoperative electron radiotherapy (IOERT) as a boost for breast cancer releases a high single dose of radiation to the breast tissue; therefore acute toxicity is of particular attention. To date there is only inadequate information available on breast cancer patients treated with IORT using electrons applied as a boost. We therefore analyzed the acute toxicity and late side effects after radiotherapy with 10 Gy as a boost with a minimum follow-up of 3 months. Methods: A total of 385 patients treated with IOERT (10 Gy with 5, 7 and 9 MeV electrons) with a dedicated robotic linac (NOVAC 7, New Radiant Technology, Aprilia, Italy) to the tumor bed during breast-conserving surgery as a boost followed by whole-breast radiotherapy (WBRT,50- 50.4 Gy; 1.8-2 Gy per fraction) were included in this study. All patients underwent a retrospective follow-up regarding acute and late side effects. Toxicities were documented using the common toxicity criteria (CTC 4.0 of the European Organization for Research and Treatment of Cancer) and normal tissues subjective, objective, management and analytic scales (LENT-SOMA). Results: The IOERT was well tolerated and the cosmetic results were good. As a side effect there were five patients with seroma. Two patients developed a secondary wound healing. Two patients developed chronic pain in the irradiated breast. Ten patients developed a grade 2 fibrosis. The remaining patients did not develop any grade 3 or 4 side effects. The observed toxicity rates were not influenced by age, tubus size, electron energy or systemic therapy. 80 patients had a follow up longer than 5 years. Three of them developed distant metastasis and one patient died. Conclusions: After IOERT of the breast using electrons we did not find any unexpected acute and late toxicity rates.