399P - Functional MRI in locally advanced rectal cancer: Can novel MRI techniques predict response to total neoadjuvant therapy?

Background

Recent advances in MRI with high resolution plays an important role in diagnosis and staging of rectal cancer. We aimed to assess the role of MRI quantitative techniques DWI/ADC and MRS in diagnosis and predicting response of rectal cancer to total neoadjuvant therapy (TNT).

Methods

The study included 38 patients with pathologically diagnosed rectal cancer who were planned to receive TNT protocol. TNT consisted of 4 cycles XELOX (oxaliplatin plus capecitabine) followed by concurrent radiotherapy (50.4 Gy/28 fractions to whole pelvis) with oral capecitabine day 1-5 each week. Before TNT, patients had baseline non-contrast MRI of rectum which was repeated 6-8 weeks after end of TNT and results were compared to assess the degree of response radiologically. Then, patients were referred to surgery. The radiological response was compared to the post-operative pathological response.

Results

Patients had mean age of 54.6 years ±10.37 with 36.8% males and 63.2% females. Following TNT, 76.9% and 23.1% patients had low anterior resection and abdominoperineal resection, respectively with 35.1% pathological complete response (PCR), 63.2% partial response and 3.8% no response. The ADC value was measured in each case before and after TNT. It ranged from 0.5-2.1 x10^-3mm²/s with mean value of 0.98 ±0.39. The ADC value significantly differentiates well to moderately from poorly differentiated carcinoma (p value = 0.001). The cut off value of ADC to predict poorly differentiated tumors was 0.85x10^-3mm²/s with sensitivity 87.5%, specificity 70%, PPV 40%, and NPV 91.3%. There was a significant increase in ADC value after TNT reflecting decreased cellularity in tumors with adequate response (p value >0.001). Choline signal to noise ratio (Cho SNR) was measured in each case before and after TNT and there was a significant association between Cho SNR ≤ 3 and PCR (p value <0.001). There was a significant negative correlation between DWI/ADC before TNT and the extent of Cho SNR reduction (p value <0.001, r=-0.42).

Conclusions

Functional MRI using non-invasive, non-contrast DWI and MRS by measuring ADC and Cho SNR can accurately diagnose rectal cancer, differentiate tumor grade and predict response to TNT.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

Ethical committee of Faculty of Medicine, Alexandria University.

Funding

Has not received any funding.

Disclosure

All authors have declared no conflicts of interest.