Partial breast irradiation with IORT using Xoft®. Experience at Catalan Institute of Oncology

ABSTRACT

Purpose or Objective external beam whole breast irradiation (WBI) for low-risk early-stage breast cancer patients after breast conserving surgery. We present the experience at our center treating patients with PBI using an IORT technic with Xoft® Axxent® Electronic Brachytherapy (eBx®) System®. Materials and Methods Between April 2019 and August 2021, 44 patients diagnosed with low-risk early-stage breast cancer who met international criteria for PBI, received IORT in a single fraction of 20 Gy to the tumor bed after lumpectomy. Toxicities and follow up were prospectively registered. Results 3 of the 44 initial patients were discarded for IORT due to non-compliance with the minimum safety distance (<1 cm) between the applicator and the skin. Of the remaining patients, 32/41 patients (78%) received a PBI, while 9/41 (22%) required adjuvant WBI due to adverse prognostic factors identified on the definitive biopsy. The most frequent risk factor was close resection margins (<2mm), present in 8/9 patients (88,8%). Two patients additionally presented sentinel node involvement and in 1 case no axillary sample was obtained. The most used IORT applicator was the 3-4 cm balloon, with most likely filling volumes between 30cc and 40 cc. For all treatments, the mean filling volume of the applicator was 45 cc and there were no complications during the irradiation procedure. Surgical bed seroma was the most common acute effect, observed in 29/41 patients (70,7%), although only 8/29 (27,5%) required drainage. We observed wound dehiscence in 7/41 cases (17%), inflammatory complications requiring antibiotics in 9/41 cases (19,5%), and 4/41 cases of hematoma (9,7%). Regarding late toxicity, at the time of the analysis it was only assessable for 37 patients. We observed low rates of local grade I fibrosis (21,6%) and only 1 case of tumor bed G2 fibrosis. Hyperpigmentation G1 was observed in 8,1% of patients and 10,8% presented occasional mild local discomfort. With median follow-up of 17.14 months (range 4-29 months), no relapses were observed, but 1 patient died from covid-19 pneumonia. Conclusion Intra operative PBI with Xoft® Axxent® Electronic Brachytherapy (eBx®) System® is a feasible approach to treat low-risk early-stage breast cancer patients. Our preliminary results show that it presents advantages over conventional WBI allowing for less toxic and shortened treatment courses while maintaining good local tumor control.