Long-term oncologic outcome of intraoperative radiotherapy (IORT) with low-energy X-rays as a tumor-bed boost in Korean patients with breast cancer

Abstract

Background: Although the use of intraoperative radiotherapy (IORT) for accelerated partial breast irradiation is growing, there are not many studies on its effectiveness specifically in Asian population. In this study, we aimed to investigate the long-term oncologic outcomes of Korean patients who received IORT with low-energy X-ray as a tumor-bed boost.

Methods: We conducted phase II, prospective, single-arm trial to evaluate the local toxicity and oncologic outcomes in breast cancer patients receiving IORT with low-energy X-rays as a tumor-bed boost (NCT02213991). Patients underwent IORT as a tumor-bed boost with low-energy X-rays (20 Gy) followed by external beam radiotherapy for whole breast irradiation (46 Gy). Patients diagnosed with early-stage breast cancer or ductal carcinoma in situ who were suitable for lumpectomy were considered eligible. Kaplan-Meier analysis was used to assess oncologic outcomes with an extended follow-up period.

Results: A total of 194 patients underwent IORT between August 2014 and September 2016 according to the protocol outlined in our study. During the median follow-up of 85.6 months, 12 cases (6.19 %) of recurrence were reported, of which 4 (2.06 %) were reported ipsilateral breast tumor recurrence (IBTR) as the first recurrence event. The 5- and 8-year IBTR rates were both 2.1 % (95 % confidence intervals (CIs), 93.8 - 98.9). The 5-year loco-regional recurrence-free survival (LRRFS), recurrence-free survival (RFS), and overall survival (OS) rates were 97.37 %, 96.32 %, and 100 %, respectively.

Conclusion: We identified the oncologic safety of IORT with low-energy X-rays as a tumor-bed boost in Korean patients during an extended follow-up period.