The Value of Magnetic Resonance Imaging to Assessing Response and Prognosis to Total Neoadjuvant Treatment (TNT) in Locally Advanced Rectal Cancer

Abstract

To investigate the potential value of magnetic resonance imaging (MRI) in assessing response and prognostic relevance to total neoadjuvant treatment (TNT) in locally advanced rectal cancer (LARC) with high risk factors. This was a retrospective study of pre-, during, and post-TNT MRI of patients with LARC with high risk factors who underwent TNT before operation. Patients received three cycles of induction chemotherapy (ICT) followed by neoadjuvant radiotherapy and 2 cycles of concurrent chemotherapy (CRT).After that, 3 cycles of consolidation chemotherapy (CCT) were delivered. Radiation dose of pelvic IMRT/VMRT was 50.4 Gy/28f. MRI scans were performed before TNT (baseline), after CRT (post-CRT) and after CCT(post-CCT), respectively. MRI parameters such as the apparent diffusion coefficient (ADC) values of tumor, T2 adjusted values of tumor (T2 values of tumor/T2 values of gluteus maximus muscle) (T2a), maximum cross-sectional area of tumor on diffusion-weighted imaging (SDWI) and T2-weight (ST2), the numbers of lymph node metastases (LNN) and diameter of lymph node (LND), were measured by two experienced readers independently. In addition, the changes in MRI parameters relative to baseline were calculated. Spearman’s correlation coefficient and Wilcoxon’s rank sum test were used to assess association between MRI parameters and complete response (CR). Cox regression was used to evaluate association between MRI parameters and OS/DFS. We analyzed MRI images of 52 patients who underwent TNT from 2015 to 2017 retrospectively. Among them, there were 22 patients (42%) who achieved CR, including 15 pathologic CR (pCR) in those who underwent surgery and 7 clinical CR (cCR). The median follow-up was 30 months (11-39 months). As to the baseline MRI parameters, only ADC was correlated with CR (r=0.312, p=0.026). 1 and 2-year OS rate of the whole cohort was 98.1% and 93.2%, respectively. 1 and 2-year DFS rate were 92.3% and 84.3%, respectively. Multivariate analysis showed that baseline T2a ≥5 (HR 0.048, 95% CI 0.009 - 0.265; p<0.001) and baseline SDWI ≥2cm2 (HR 17.875, 95% CI 1.854-172.306; p=0.013) were independent prognostic factors for unfavorable DFS. There were 25 patients who had complete baseline, post-CRT, and post-CCT MRI images. For these patients, baseline ADC (r=0.544, p=0.005), post-CCT ADC (r=0.522, p=0.007), ΔADC (post-CCT relative to baseline) (r=0.522, p=0.007), post-CRT LNN (r=-0.400, p=0.047), ΔLNN (post-CRT relative to baseline) (r=0.677, p=0.000199), and ΔLND (post-CRT relative to baseline) (r=0.594, p=0.002) were correlated with CR. ΔSDWI (post-CRT relative to baseline) >30 cm2 (HR 0.036, 95% CI 0.004 - 0.363; p=0.005) was independent prognostic factor for better DFS. Baseline ADC, ΔADC, ΔLNN, and ΔLND seem to have correlation with response to TNT. T2 adjusted value, baseline SDWI and ΔSDWI > 30 cm2 might relate to better DFS.