Comparison of Pre and Post Treatment Magnetic Resonance Features of Rectal Cancer Between Patients Undergoing Long and Short Course Neoadjuvant Treatment at the Kenyatta National Hospital

Abstract

Study Background: The treatment of locally advanced rectal carcinoma involves the use of neoadjuvant chemo radiation. The types of neoadjuvant treatment offered to these patients can be long-term or short-term. The choice of course of treatment to be undertaken remains under debate. No clear reason for the choice of treatment is given. Short course treatment can be preferred in cases of proximally located tumors, cost-effectiveness or convenience since it takes a shorter time. Long course treatment is preferred in cases of more distal tumors. Thereafter, MRI is used for follow-up evaluation of the disease to assess for response to the neoadjuvant treatment. During MRI evaluation, restaging of the disease is done which then determines the next step treatment / management following neoadjuvant therapy and eventually determines the treatment outcome/success of treatment for these patients. Evaluation of rectal carcinoma using MRI involves the use of anatomical and functional techniques to assess the morphology and biology of the tumor therefore increasing the confidence of assessing for tumor response on MRI. There is no local study done to assess the MRI findings of rectal tumor response post CRT or compare the tumor response between patients who have undergone long course and short course treatment. Study Objective: This study assessed the pre-treatment and post-treatment MRI features of rectal tumors that underwent either long course or short course treatment, categorized and compared the treatment response categories between the two groups. Study design and site: This was a comparative cross-sectional study done at the Kenyatta National Hospital Radiology and cancer treatment center department with the MRI treatment response category as the outcome and the treatment duration as the exposure of treatment. Study participants and methods: Adult patients with rectal cancer who had undergone both long and short courses of neoadjuvant treatment were included in this study. A complete enumeration was done where all patients on post treatment follow up were included in the study; 25 patients on long neoadjuvant treatment group and 15 patients on short course neoadjuvant treatment group. Data management: Statistical Package for Social Sciences version 28 was used for analysis. Demographic and clinical characteristics of the patients were analyzed and presented as frequencies and percentage for categorical data, and as means with standard deviation or median with interquartile range for continous data. Assessment for the response by comparing the changes in tumor size, T2w signal intensity, DWI/ADC map, ADC values on the ADC map were done with the use of McNemar’s test and Paired Sample t-test. The difference in tumor response in those who had long course versus short course CRT was done with the use of Pearson Chi-square test. All statistical tests were considered significant where the p-value < 0.05. Significance of the study: This study will aid in assessing the MRI treatment features and give surrogate information on whether either of the two treatment forms are similar in their outcome or not. Results: Of the 40 patients included in the study, 65% were female and 35% were male. The median age was 54.7 years with the youngest being 24 years and the oldest being 90 years. The xv average time to repeat MRI was 7.05 weeks. Majority of the patients undergoing long course treatment were noted to have bulkier low level disease with the majority having T3d staging. A larger diameter of residual disease (mean=2.37 cm) and higher fibrosis (mr-TRG mean of 3.83) was seen in the long course group. An improvement in the CRM status was noted in the short course group which could be attributed to less bulky disease initially. A rise in ADC value was also seen in the patients who underwent long course treatment (M= 1.91). An overall improvement in nodal disease was noted. However residual nodal disease was present in the long course group. Conclusion: This study established that the overall radiological response to treatment was better in the long course group when compared to the short course group. This result may however have been secondary to the smaller number of short course patients sampled. Less bulky disease (T3a-T3c tumours) were more likely to have short course treatment recommended while low level, bulky disease with sphincter involvement were more likely to have long course treatment recommended. An increase in ADC values was established to have a role in the indication of tumour response to treatment