A Phase II Study Evaluating the Effect of Intensity Modulated Postmastectomy Radiation Therapy on Implant Failure Rates in Breast Cancer Patients With Immediate, 2-Stage Implant Reconstruction With an MRI Imaging Correlative Substudy

Abstract

BackgroundPostmastectomy radiation therapy (PMRT) is a mainstay in the adjuvant treatment of node-positive breast cancer, but it poses risks for women with breast reconstruction. Multi-beam intensity-modulated radiation therapy (IMRT) improves dose conformality and homogeneity, potentially reducing complications in breast cancer patients with implant-based reconstruction. To investigate this hypothesis, we conducted a single-arm phase II clinical trial of breast cancer patients who underwent mastectomy/axillary dissection and prosthesis-based reconstruction. MethodsThe primary endpoint was the rate of implant failure within 24 months of permanent implant placement, which would be considered an improvement over historical controls if below 16%. Implant failure (IF) was defined as removal leading to a flat chest wall or replacement with another reconstruction. Patients were analyzed in two cohorts. Cohort 1 (RT-PI) received RT to the permanent implant (PI). Cohort 2 (RT-TE) received RT to the TE. Implant failure rates, adverse events, and quality of life (QOL) were analyzed. Follow-up/post-RT assessments were compared to the baseline/pre-RT assessments at 3-10 weeks after exchange surgery. A subgroup underwent serial MRIs to explore the association of MRI-detected changes with capsular contracture, a known adverse effect of RT. ResultsBetween June 2014 and March 2017, 119 women were enrolled. Cohort 1 included 45 patients, and Cohort 2 had 74 patients. Among 100 evaluable participants, 25 experienced IF during the study period. IF occured in 8/42 (19%) and 17/58 (29%) in Cohorts 1 and 2, respectively. Among the IFs, the majority were due to capsular contracture (13), infection (7), exposure (3), and other reasons (2). Morphological shape features observed in longitudinal MRI images were associated with the development of Baker grade 3-4 contracture. ConclusionsThe rate of implant failure in reconstructed breast cancer patients treated with IMRT was similar to, but not improved over, conventional, 3D-conformal methods. MRI imaging features show promise for predicting capsular contracture but require validation in larger studies.