Comparing the Outcome of Boost Dose of Intraoperative Radiotherapy with Electron (IOERT) and Low-kV X-Ray (IOXRT) and External Beam Radiotherapy (EBRT) in Breast Cancer After Neoadjuvant Chemotherapy

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Background: In the large breast tumors or locally-advanced breast cancers, breast conserving surgery (BCS) after neoadjuvant chemotherapy (NACT) had an acceptable local control, but greater risk of recurrence. Adding boost dose radiation to whole breast radiotherapy is involved with a reduced risk of recurrence. Boost radiotherapy can be delivered in 3 methods, including (1) external beam radiotherapy (EBRT), (2) intraoperative radiotherapy with electron (IOERT), and (3) intraoperative radiotherapy with low-kV X-ray (IOXRT). Objectives: This study compared the outcomes of these 3 methods with each other. Methods: Within 60 months, 217 unselected breast cancer patients in Cancer Research Center of Shahid Beheshti were under treatment with BCS after NACT. They received boost dose radiation in 3 groups; 115 patients in the EBRT group, 39 patients IOXRT group, and 63 patients in the IOERT group. All of them received WBRT after surgery. Results: The patients had large tumors or stage 3 breast cancer. Local recurrences were 1 (2.5%) in IOXRT, 2 (3.2%) in IOERT, and 1 (0.9%) in EBRT groups. Systemic recurrences were 4 (10.3%) in IOXRT, 10 (15.9%) in IOERT, and 16 (13.9%) in EBRT groups. Deaths were 3 (7.7%) in IOXRT, 2 (3.2%) in IOERT, and 10 (6.9%) in EBRT groups. Patients with any events were 4 (10.3%) in IOXRT, 11 (17.5%) in IOERT, and 33 (15.2%) in the EBRT group. Death due to distant metastases was lower in IOERT group, but it was not significant. No significant difference was observed in disease-free survival (DFS) among 3 groups. IOXRT group had non-significant, lower events, and better DFS. Especially, in non-PCR (non-pathologic complete response) patients, multivariate COX analysis showed better outcome (DFS) in IOXRT group (HR = 0.50), although it was not significant (P = 0.53). Conclusions: Intraoperative radiotherapy (IORT or IOXRT) as tumor bed boost during BCS after NACT had at least non-inferiority compared with EBRT. In non-PCR patient, IOXRT group had non-significant better outcomes (DFS).