Evaluation of an Objective MRI-Based Tumor Regression Grade (mrTRG) Score and a Subjective Likert Score for Assessing Treatment Response in Locally Advanced Rectal Cancers-A Retrospective Study

Purpose:  Magnetic resonance imaging (MRI) with the help of MRI-based tumor regression grade (mrTRG) score has been used as a tool to predict pathological tumor regression grade (pTRG) in patients of rectal cancer post-neoadjuvant chemoradiation. Our study aims to evaluate the ability of MRI in assessing treatment response comparing an objective mrTRG score and a subjective Likert score, with a focus on the ability to predict pathologic complete response (pCR). Methods:  Post-treatment MRI studies were retrospectively reviewed for 170 consecutive cases of histopathologically proven rectal cancer after receiving neoadjuvant chemoradiation and prior to surgery by two oncoradiologists blinded to the eventual postoperative histopathology findings. An objective (mrTRG) and a subjective Likert score were assigned to all the cases. Receiver operating characteristic curves were constructed to determine the ability of Likert scale and mrTRG to predict pCR, with postoperative histopathology being the gold standard. The optimal cutoff points on the scale of 1 to 5 were obtained for mrTRG and Likert scale with the greatest sum of sensitivity and specificity using the Youden Index. Results:  The most accurate cutoff point for the mrTRG to predict complete response was 2.5 (using Youden index), with a sensitivity of 69.2%, specificity of 69.6%, positive predictive value (PPV) of 85.6%, negative predictive value (NPV) of 46.4%, and accuracy of 69.3%. The most accurate cutoff for the Likert scale to predict complete response was 3.5, with a sensitivity of 47.5%, specificity of 89.1%, PPV of 91.9%, NPV of 39.4%, and accuracy of 59%. mrTRG had a lower cutoff and was more accurate in predicting pCR compared to Likert score. Conclusion:  An objective mrTRG was more accurate than a subjective Likert scale to predict complete response in our study.

MRI in rectal cancer patients on 'watch and wait': patterns of response and their evolution

PURPOSE

Evaluate MR patterns of response and their evolution in rectal cancer patients on watch and wait (WW).

METHODS

We retrospectively reviewed 337 MRIs of 60 patients (median follow-up: 12 months; range: 6-49 months). Baseline MRIs (available in 34/60 patients) were evaluated for tumor morphology, location, thickness, circumferential involvement, nodal status and EMVI. First post-treatment MRIs (in all patients) were additionally evaluated for pattern of response on T2 and DWI. Change in post-treatment scar thickness and scar depth angle between the first and second post-treatment scans was also evaluated. Evolution of the response pattern/recurrence were evaluated till the last available scan.

RESULTS

On the baseline scans, 20/34 (59%) patients had polypoidal tumor with 12/20 having ≤ 25% circumferential wall involvement. We saw five patterns of response-normalized rectal wall (2/60-3%), minimal fibrosis (23/60-38%), full thickness fibrosis (16/60-27%), irregular fibrosis (11/60-18%) and split scar (6/60-10%), with 2/60 (3%) showing possible residual disease. On the first post-treatment scans, 12/60 (20%) had restricted diffusion, with 3/12 having persistent restriction till last follow-up. Post-treatment fibrosis/split scar remained stable in 44/60 (73%) cases and improved further in the rest. 9/60 (15%) patients developed regrowth/recurrence. Patients with recurrence had < 10 mm scar thickness and < 21° change in scar angle between the first and second post-treatment MRIs.

CONCLUSION

Most patients on WW protocol developed minimal or full thickness fibrosis, majority of which remained stable on follow-up.

Dose Escalation Using Magnetic Resonance Guided High-Dose-Rate Endorectal Brachytherapy to Enhance Clinical Response after Neoadjuvant Radiotherapy in Rectal Adenocarcinoma

PURPOSE/OBJECTIVE(S)

To assess the proportion of patients with rectal adenocarcinoma achieving clinical complete response after neoadjuvant chemoradiation (NACTRT) and MR guided endorectal brachytherapy boost (MR-ERBT) MATERIALS/METHODS: Patients with rectal cancers (T2-T4/N0-N+) treated with concurrent chemoradiotherapy (50Gy/25# with Capecitabine) between June-2017 to April-2022. Post RT, patients having residual non-circumferential lesions <8cm in length were administered escalated-dose MR-ERBT with Ir192 HDR source. A median dose of 12Gy (8-15Gy) in 3 (2-3) fractions at 3-5 day intervals was delivered using MR-ERBT after external radiation. Data on near complete/complete clinical response (nCR/cCR) rates, local regrowth rates and clinical outcome were collected for analysis.

RESULTS

Of the 145 patients who received MR-ERBT, majority were staged as T3(78.7%) and N1-2 (77.5%) rectal cancers. Median tumor length was 4cm and 123 (85%) of the tumors were located in the lower rectum (0-5cm from anal verge). Seventy-six (52%) patients achieved cCR or nCR (37 cCR, 39 nCR) and were advised observation or watch and wait (WW) management. The 69 patients having partial response were advised surgery. The patients having nCR 16 (29%) underwent resection, of these 10 (62%) had pathological complete response (pCR). The patients with partial or poor response, 57 underwent resection and of these 11 (19%) had pCR, 12 patients refused surgery due to fear of permanent stoma and continued to be on follow up. Of the 79 patients undergoing resection, 36 (45.5%) had sphincter preserving surgeries. At the median follow up of 30 months, local regrowth was seen in 8 (10.5%) of patients on WW and 6 were surgically salvaged while other 2 had synchronous metastatic relapse. Thus, 56 (41%) achieved organ preservation and continued to be on WW management. Twelve (8,2%) patients developed distant metastasis in the entire cohort, 3 in the WW group and 9 in the resected group. There were no pelvic recurrences seen in the resected patients. The disease-free survival at 3 years were (96.1% vs 89% Observation vs. resected (p_0.05) respectively. The overall survival at 3 years were (93% vs 98% Observation vs. resected (p_0.44) respectively. Late rectal toxicity was observed in 16(11%) patients on observation CONCLUSION: Dose Escalated MR-EBRT is an effective and safe method to enhance complete clinical response, thus improving the rate of organ preservation for distal rectal cancers.

Imaging Recommendations for Diagnosis, Staging, and Management of Small Bowel and Colorectal Malignancies

Small bowel malignancies are rare, though colorectal cancers are common. This article reviews the current imaging recommendations for small bowel and colorectal malignancies. Contrast-enhanced computed tomography (CT) is the imaging modality of choice for diagnosis/staging/response evaluation/follow-up of the small bowel and colonic tumors. Magnetic resonance imaging of the pelvis with high-resolution T2-weighted images in sagittal, oblique axial, and coronal planes is the imaging modality of choice for staging/response evaluation of anorectal tumors. CT colonography may be utilized as a tumor screening modality, alternative to colonoscopy.

Gastrointestinal Stromal Tumor (GIST) from esophagus to anorectum - diagnosis, response evaluation and surveillance on computed tomography (CT) scan

Gastrointestinal stromal tumor (GIST) are the most common non epithelial tumor of the gastrointestinal (GI) tract. They arise from interstitial cells of Cajal present in the myenteric plexus. They can also arise outside the GI tract from mesentery, retro peritoneum and omentum. With the advent of new targeted molecular therapy c- tyrosine kinase inhibitor (Imatinib), it has become important to differentiate between response and pseudo-progression of the disease as response evaluation criteria for GIST are different from Response Evaluation Criteria in Solid Tumors (RECIST). Purpose of this pictorial essay is to enumerate the characteristic CT features of GIST, and discuss atypical features and response evaluation criteria.

Can Post-Treatment MRI Features Predict Pathological Circumferential Resection Margin (pCRM) Involvement in Low Rectal Tumors

The MERCURY II study demonstrated the use of MRI-based risk factors such as extramural venous invasion (EMVI), tumor location, and circumferential resection margin (CRM) involvement to preoperatively predict pCRM (pathological CRM) outcomes for lower rectal tumors in a mixed group of upfront operated patients and patients who received neoadjuvant treatment. We aim to study the applicability of results of MERCURY II study in a homogeneous cohort of patients who received neoadjuvant chemoradiation (NACTRT) prior to surgery. After Institutional Review Board approval, post NACTRT restaging MRI of 132 patients operated for low rectal cancer between 2014 and 2018 were retrospectively reviewed by two radiologists for site of tumor, EMVI status, distance from anal verge (< 4 or > 4 cm), and mrCRM positivity. Findings were compared with post surgery pCRM outcomes using Fisher's exact test. Only 9/132(7%) patients showed pCRM involvement on histopathology, 8 of them being CRM positive on MRI (p = 0.01). The positive predictive value (PPV) of mrCRM positive status and pCRM status was 12.7% (95% CI: 9.7-16.5%), while the negative predictive value was 98.5% (95% CI: 91.4-99.8%) (p = 0.01). EMVI positive and anteriorly located tumors showed higher incidence of pCRM positivity but were not found to be significant (15% vs 5.2% and p = 0.13 and 8.6% vs 2.1% and p = 0.28, respectively). Unsafe mrCRM was the only factor significantly associated with pCRM positivity on post neoadjuvant restaging MRI. Tumors less than 4 cm from anal verge, anterior tumor location, and mrEMVI positivity did not show statistically significant results to predict pCRM involvement.