Nomogram For Predicting The Risk Of Locoregional Recurrence In Patients Treated With Accelerated Partial-Breast Irradiation

59 Background: There are limited tools to guide clinicians regarding the risk of locoregional recurrence (LRR) in patients wishing to pursue APBI. The purpose of this study was to develop a nomogram taking into account clinicopathologic features to predict LRR in patients treated with APBI for early stage breast cancer.A total of 2,000 breasts (1,990 women) were treated with APBI at William Beaumont Hospital (N=551) or on the ASBrS MammoSite Registry Trial (N=1,449). Techniques included multiplanar interstitial catheters (N=98), balloon-based brachytherapy (N=1,689), and 3D conformal radiotherapy (N=213). Clinicopathologic variables were gathered prospectively. A nomogram was formulated utilizing the Cox Proportional Hazards Regression model to predict for LRR. This was validated by generating a bias-corrected index and cross-validated with a C-index.Median follow-up was 5.5 years (0.9 to 18.3). Of the 2,000 cases, 435 were excluded due to missing data. Univariate analysis found that age <50, pre/perimenopausal status, close/positive margins, ER negativity, and high grade were associated with a higher frequency of LRR. These five independent covariates were used to create adjusted estimates, weighting each on a scale of 0 to 100. The total score is identified on a points scale to obtain the probability of an LRR over the study period. The model demonstrated good concordance for predicting LRR with a C-index of 0.641.The formulation of a practical, easy-to-use nomogram for calculating the risk of LRR in patients undergoing APBI will help guide the appropriate selection of patients for off-protocol utilization of APBI.