The Role of Magnetic Resonance Imaging in The Evaluation of Response of The Locally Advanced Rectal Cancer to The Chemoradiotheraphy

Aim: Investigate the role of Magnetic Resonance Imaging (MRI) in the evaluation of response of the locally
advanced rectal cancer to the chemoradiotheraphy (CR T).
Patients and Methods: T2-weighted and Diffusion Weighted Imaging (DWI) of 24 cases with locally advanced
rectal cancer who have undergone total mesorectal excision 6-8 weeks following the CRT between 2015 and
2020 were evaluated retrospectively. The evaluated radiological parameters were as follows; Tumor morphology,
localization, length, mrT/mrN stages, and extramural vascular invasion (EMVI). Post-CRT MRI residue scoring
was performed (0: No residual tumor, 1: No significant residual tumor, fibrotic wall thickening, 2: Residual tumor
present). Regression grading was as follows; 1: No tumor, 2: Good response, mostly fibrosis, 3: Fibrosis and
mucin more than 50%, 4: Slight response, 5: No response.
Results: There was a significant decrease in the craniocaudal length of tumor and a significant increase
in the mean ADC of tumor after CRT (p=0.001). A significant and high correlation was observed between
histopathological T (pT) and post-CRT mrT (r=0.54, p=0.006). There was a significant correlation between pre-
CRT EMVI and perineural invasion (PNI) (r=0.53, p=0.008). A significant correlation was found between residue
scoring and regression grading (r=0.6; p=0.001), pT (r=0.48; p=0.02), and tumor length (r:0.51; p=0.01). There
was a significant correlation between regression grading and EMVI (r=0.43, p=0.036), PNI (r=0.46, p=0.02), pT
(r=0.41; p=0.048), pN (r=0.55; p=0.006), and metastatic/total lymph node ratio (r=0.46; p=0.02).
Conclusion: Post-CRT MRI is highly correlated with postoperative pathological evaluation of the locally
advanced rectal cancer. MRI is highly successful in re-staging as well as primary staging. The evaluation of
treatment response by MRI regression grading may contribute to the surgical planning.