Association Between Radiographic Mastectomy Flap Thickness and Risk of Post-Radiation Therapy Breast Reconstruction Complication

Abstract

Breast reconstruction after mastectomy is an important component of holistic care for many women with breast cancer. Post-mastectomy radiotherapy yields a large survival advantage for well-selected patients, and is a vital component of cancer care, however, it can raise the risk of reconstruction complications. Several risk factors, such as smoking and diabetes, have been implicated in complication risk. This study sought to assess the relationship between reconstruction complication risk and mastectomy flap thickness as measured radiographically at CT simulation. Women with breast cancer who had undergone mastectomy and immediate tissue expander (TE) placement and received post mastectomy radiation therapy at a single institution were identified. Those patients with available digital CT-simulation records were included. Flap thickness was measured using both 2D and 3D methods. In a 2D method fashion, flap thickness was measured as the linear distance between the TE and the skin at the top, bottom and center of the TE. For a 3D estimation, the entire flap as defined as the tissue between TE and the skin-air interface was contoured and its volume calculated. Demographic and health variables and all reconstruction complications were recorded during stage I (after TE placement) and stage II (after permanent implant) including: flap necrosis, TE or implant migration, TE or implant rupture, infection, seroma, TE or implant removal, exposure and/or dehiscence, contracture, and capsulotomy. Flap thickness was correlated to risk of complications using Cox regression. Receiver operating characteristic curves were created to identify threshold values for flap thickness. A total of 87 patients met the inclusion criteria. A total of 132 breasts with implants were studied. The incidence of flap necrosis was 12.1% during phase I and 2.7% during phase II of reconstruction. The rates of TE removal was 9% and the rates of permanent implant removal was 7%. On UVA, lower 2D flap thickness and lower 3D flap volume were associated with significantly higher combined complications during both phases of reconstructions with hazard ratio (HR) of 0.43 (p=0.04) and HR 0.9 (p=0.03), respectively. Threshold values were identified: average flap thickness less than 8.9 mm and flap volume less than 259cc were correlated to worse outcomes HR 0.3 (p=0.04) and HR 0.35 (p=0.02). These data support the notion that lower flap thickness is associated with a higher risk of reconstruction complications. This series represents the only analysis of the relationship between radiographic mastectomy flap thickness and reconstruction risk known to the authors. These data raise the possibility that the risk of reconstruction toxicity could be estimated more accurately after CT simulation, potentially facilitating prophylactic intervention for women at high risk.