Abstract P4-16-08: INTRAOPERATIVE ELECTRON RADIOTHERAPY IN EARLY STAGE BREAST CANCER. A SINGLE-INSTITUTION EXPERIENCE

Abstract

Abstract Background: Women with early stage disease not only have a better prognosis, but also have the opportunity to preserve their breasts. Despite the positive evidence and outcomes for breast-conserving therapy (BCT), many women are unable or unwilling to undergo 5–7 weeks of external-beam radiotherapy (EBRT). We report the results of a single-institution phase II trial of accelerated partial breast irradiation (APBI) using a single dose of intraoperative electron radiotherapy (IOERT) in patients with low risk early stage breast cancer. Methods and materials: From July 2006 to December 2009, 226 patients suitable for BCT were enrolled in a phase II trial with IOERT as radical treatment immediately after surgical resection. All patients had biopsy proven cancer. After the surgeon temporarily re-approximated the excision cavity, a dose of 21 Gy using IOERT was delivered to the tumor bed with a margin of 2 cm laterally. Results: No acute reactions were reported after irradiation. Three patients experienced a transient edema. In 7 others a haematoma was observed. No cases of liponecrosis were observed. With a mean follow-up of 49 months (range 31–66 months), only one case of local recurrence has been reported. The observed toxicity was considered acceptable. As to cosmetic results, at 6 months after the end of IORT, 71/226 patients (31.4.%) had a score of 2 for symmetry and contour (asymmetry exhibited by 1/3 or less of volume breast), while 19/226 (8.4%) had a score 3 (asymmetry greater than 1/3 of breast volume). These findings remained unchanged at the following examinations. No breast oedema, discoloration at site or scar prominence were observed. Discussion: IOERT has significant advantages compared to other post-operative APBI approaches. The surgical re-approximation of the tumor bed, combined with the high quality of electron beam radiation, generates substantially more uniform dose distributions. IOERT offers the advantage of an excellent delineation of the tumor bed under visual control and high sparing of normal tissue, including the skin. IOERT delivers a very high biologically dose at the time of the surgery, when residual tumor cells are more rapidly proliferating. IOERT is insensitive to chemotherapy sequencing since all of the radiation is given during the surgery. IOERT offers low-risk women the possibility of a one-day procedure to treat their cancer and preserve their breast. The results of our study are very encouraging compared with other series with IOERT or APBI. The absolute recurrence rate of 0.4% and the recurrence rate per year of 0.2% of the present study are lower compared to the ones from the largest series with IOERT ever published (3.6% and 1.2%, respectively) (1). Conclusion: APBI using a single dose of IOERT can be delivered safely in women with early, low risk breast cancer. A longer follow-up is needed to ascertain its efficacy compared to that of the current standard treatment of whole breast irradiation.