Abstract P1-10-20: A multi-center trial of intra-operative electronic brachytherapy during breast conservation surgery for early stage breast cancer: Early results of unplanned boost participants (2017)

Abstract Objective To assess the safety and efficacy of single-fraction, intra-operative radiation therapy (IORT) delivered as a boost using the Xoft® Axxent® Electronic Brachytherapy System® (eBx®) immediately following surgical resection for treatment of early stage breast cancer. Methods This phase 4, open-label, single-arm, prospective, non-randomized trial is still enrolling participants and is currently being conducted at 26 hospitals in the USA (25) and Portugal (1). 878 participants with biopsy-proven ductal carcinoma in situ (DCIS) or invasive ductal carcinoma who met the inclusion criteria underwent lumpectomy followed by single-fraction IORT to the lumpectomy cavity. Briefly, a small, presterilized lead shield piece was placed on the chest wall to reduce the dose to the ribs, and then a balloon applicator, suitable to the surgical bed, was placed in the lumpectomy cavity and inflated with saline (30-75 cc); skin was temporarily closed over the balloon and ultrasound was used to confirm a balloon surface-to-skin distance ≥ 1.0 cm. The Xoft System was used to deliver the 20 Gy dose at the balloon applicator surface. The balloon was deflated, lead shield and balloon removed and the surgical site sutured. Upon the presence of additional risk factors, 37 participants subsequently received whole breast radiation therapy (WBRT); thus, these participants received an unplanned IORT boost and were removed from the primary analysis but will continue to be followed for the duration of the 10-year study. Cosmesis (Harvard Scale) was assessed in this subset of participants. The primary outcome for the main trial is recurrence of ipsilateral breast tumor at 5 years. Trial Registry: ClinicalTrials.gov; Identifier: NCT01644669. Early Findings 37 boost participants received WBRT (up to 50 Gy) after IORT (36 received the prescribed 20 Gy dose; one received 14 Gy). Mean follow-up time was 430 days (range 13-1119). Mean age at IORT was 62 years (range 45-78). Boost participants had either DCIS (N=5) or invasive ductal carcinoma (N=32). The DCIS nuclear grade was high (N=3), intermediate (N=1), or low (N=1). Invasive cancers were Grade 1 (N=15), 2 (N=10), 3 (N=6), or unknown (N=1). 29 participants had T1, 3 had T2, and 5 had Tis lesions. Mean tumor size was 13.04 ± 10.26 mm. For the two participants who have reached 3-year follow-up, cosmesis was excellent (N=1) and fair (N=1). For the six participants who have reached 2-year follow-up, cosmesis was excellent (N=4), good (N=1), and fair (N=1). There was one serious adverse event with a Grade 3 for skin necrosis. The most frequent side effects were seroma (10%), edema (9%), pain (9%), erythema (6%), and induration (5%). There have been no deaths, recurrences, or new primary tumors among the boost participants to date. Conclusions Early results from this multi-center trial suggest that IORT as a tumor-bed boost using the Xoft Axxent eBx System at the time of breast conservation surgery is safe and has low morbidity. To date, the majority of participants receiving an unplanned IORT boost have had excellent to good cosmetic results and the majority of adverse events have been low-grade. Funding Funded by Xoft, Inc., a subsidiary of iCAD, Inc. Citation Format: Syed AMN, Chang H, Schwartzberg B, Bremner A, Boylan S, Lopez-Penalver C, Vito C, Davis M, Dooley W, Chakravarthy AB, Coomer C, Proulx G, Golder S, Ivanov O, Fernandez K, Farha MJ, Gonzalez V, Wengler C, Bhatnagar A, Neuner GA, Kopkash K, Rahman S, Costa P. A multi-center trial of intra-operative electronic brachytherapy during breast conservation surgery for early stage breast cancer: Early results of unplanned boost participants [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P1-10-20.