Baseline Diffusion Weighted Magnetic Resonance Imaging to Predict Recurrence of Anal Squamous Cell Carcinoma (ASCC) Following Chemoradiotherapy

Abstract

The aim of this study was to investigate the added value of baseline diffusion weighted MRI (DWI) heterogeneity analysis to predict response to chemoradiotherapy (CRT) in patients with primary squamous cell carcinoma of anal canal. We have previously demonstrated that MRI heterogeneity features may have an added value in response prediction in ASCC, here, we present the effect of DWI texture features on disease free survival in an expanded patient cohort. An IRB waiver was obtained for retrospective analysis of standard of care MRI including diffusion weighted sequences from consecutive patients with ASCC undergoing CRT treatment between 2010 and 2016. Whole tumor 3D volume of interest (VOI) was manually delineated on apparent diffusion coefficient (APC) parametric maps with reference to T2 & diffusion weighted imaging by two experienced readers in consensus generating 76 imaging features/VOI. Primary endpoint was disease recurrence (local or metastatic). Patients were censored either at time of event or last follow up. Kaplan Meier survival curves with log rank p-values were calculated for clinic-pathological variables. Most predictive univariate imaging features were selected based on their highest permutation based importance using Random Forest algorithm for survival. 65 patients were included in the current analysis (42 female, 23 male, median age 60 (range 37-85)). 33/65 patients had T3 or T4 disease and 48/65 were node positive. 43 patients achieved a complete response (CR) on re-staging MRI at 10-12 weeks post CRT. Median follow-up was 36 months (2-102). Recurrence occurred in 20/65 patients. Higher T stage (T3/T4), node positivity, gender and presence of CR alone were not significantly associated with improved disease free survival (p=0.52, 0.84, 0.28 and 0.3, respectively). Five baseline DWI imaging features with highest importance were found to be significantly associated with recurrence free survival: ADC maximum, ADC standard deviation, ADC CoV, ADC Log Entropy 1.5, ADC Range (HR>1, p < 0.001). Baseline ADC may have a role in predicting long term outcome in patients with ASCC undergoing CRT treatment and warrants further investigation in prospective trials.