607 Background: IORT for breast cancer using either electrons or low-energy x-rays is of increasing interest over the last few years. In our institution, IORT is delivered by a mobile x-ray source (Intrabeam™) producing isotropic 50 kV x-ray fields. Because this treatment method includes single high doses to the normal breast tissue, careful and long-term evaluation of early and late toxicity is mandatory. To date there are still fewdata on long-term follow-up of patients treated with low-energy x-rays. Methods: Between 2/02 and 12/06 204 breast cancer patients received IORT either as a tumour-bed boost (133) followed by 46 Gy external beam radiotherapy (EBRT) or as partial breast irradiation (PBI) only (71). Median age was 66.4 years (35–95), median tumour size was 9 mm (1–45). Spherical applicators (median 4. 0 cm) were inserted into the tumour-cavity and a single dose of 20 Gy was given. Follow-up (f/u) included physical examination and ultrasound 1 week, 2 months, then every 6 months after therapy and mammography at yearly intervals. Radiobiological modelling of the expected spatial distribution of late reactions was done for typical cases using the linear-quadratic model with special consideration of relative biological effectiveness, spatial dose distribution and dose rate. Results: Median f/u was 28 months (1–56). Minor postoperative side effects included erythema (5%), delayed wound healing (4%), mastitis (1%) and hematoseroma (4%). A fibrotic induration of the tumour bed was observed in 9, 18, 24, 23, 26% and 24% of the patients at 2, 6 12, 24, 36 and 48 month f/u. These fibrosis rates were distributed equally in both groups. Reoperation was required in 2 patients after 10 (fibrosis) and 12 months (fat necrosis). Conclusions: Although two thirds of the patients were treated with a combination of IORT and EBRT, acute reactions in all patients were mild. A fibrotic induration confined to the tumourbed was observed in up to 25% of all patients after 2 years. The low level of clinically observed late reactions so far is in agreement with predictions from radiobiological modelling. No significant financial relationships to disclose.
Clinical aspects of intraoperative radiotherapy in early breast cancer: short-term complications after IORT in women treated with low energy x-rays
