Accuracy of MRI for predicting the circumferential resection margin, mesorectal fascia invasion, and tumor response to neoadjuvant chemoradiotherapy for locally advanced rectal cancer

Findings in magnetic resonance imaging for restaging locally advanced rectal cancer

PURPOSE

We aimed to assess the prognostic value of restaging magnetic resonance imaging (MRI) in rectal cancer after neoadjuvant therapy and compare long-course chemoradiotherapy (LC-CRT) to short-course radiotherapy with delayed surgery (SCRT-delay).

METHODS

This retrospective study included 267 patients with locally advanced rectal cancer (LARC) operated on between January 2016 and April 2019, all of whom received either LC-CRT or SCRT-delay in the neoadjuvant setting. The primary outcomes were overall survival (OS) and cancer-specific survival (CSS) based on radiological response assessed using the magnetic resonance tumor regression grade (mrTRG).

RESULTS

In the LC-CRT group, cumulative 1-, 3-, and 5-year OS rates were 94.8%, 86.4%, and 79.0%, while in the SCRT-delay group, they were 83.3%, 68.9%, and 68.9% (P = 0.017). For CSS in the LC-CRT group, cumulative rates were 96.9%, 90.3%, and 85.0%, and in the SCRT-delay group, they were 88.6%, 81.4%, and 81.4% (P = 0.222). There were no significant differences in total histological response rates or local recurrence rates between the treatment groups. The good and moderate response group (mrTRG 1-3) had significantly better cumulative 1-, 3-, and 5-year OS and CSS compared to the poorer response group (mrTRG 4-5) (P = 0.023 for OS and P = 0.048 for CSS).

CONCLUSION

Unfavorable MRI response is a sign of poor prognosis in LARC. SCRT-delay is comparable to LC-CRT concerning the oncological outcome.

Predicting Positive Radial Margin on Restaging MRI of Patients with Low Rectal Cancer: Can We Do Better?

Objective  The aim of this study was to characterize the tissue involving the margin and study if this information will affect margin prediction on restaging magnetic resonance imaging (MRI) in low rectal adenocarcinoma (LRC) patients treated with neoadjuvant long-course chemoradiotherapy (LCCRT). Methods  In this retrospective study of nonmetastatic LRC (distal margin <5 cm from the anal verge) treated with LCCRT followed by surgery, a radiologist blinded to outcome reread the restaging MRI and documented if the radial margin was involved by tumor, fibrosis, or mucin reaction using T2 high-resolution (HR) and diffusion-weighted imaging (DWI). The diagnostic performance of tumor-involving margin on restaging MRI was assessed using surgical histopathology as a reference. Interobserver agreement between three independent radiologists was assessed in a subset. Results  We included 133 patients (80 males and 53 females) with a mean (range) age of 44.7 (21-86) years and 82% of them had well or moderately differentiated adenocarcinoma. Baseline MRI showed T3 ( n  = 58) or T4 ( n  = 60) disease in 89% of the patients. The pathological margin was positive in 21% ( n  = 28) cases. In restaging MRI, the circumferential resection margin (CRM) ≤1 mm in 75.1% ( n  = 100) cases and MRI predicted tumor, fibrosis, and mucin reaction at the margin in 60, 34, and 6%, respectively, and histopathology showed tumor cells in 33, 14.7, and 16.6% of them, respectively. LRC with tumor-involving margin and bad response (MR tumor regression grade [mr-TRG] 3-5) on restaging MRI had fourfold increased risk of positive pathological circumferential resection margin (pCRM). There was moderate and fair inter-reader agreement for the tissue type involving the CRM ( κ  = 0.471) and mr-TRG ( κ  = 0.266), p  < 0.05. The use of both distance criteria and tumor-involving margins improved the diagnostic accuracy for margin prediction from 39 to 66% on restaging MRI. Conclusions  Margin prediction on restaging MRI can be improved by characterizing the tissue type involving the margin in low rectal cancer patients. The inter-reader agreement was moderate for determining the tissue type.

Watch-and-Wait Approach to Rectal Cancer: The Role of Imaging

The diagnosis and treatment of rectal cancer have evolved dramatically over the past several decades. At the same time, its incidence has increased in younger populations. This review will inform the reader of advances in both diagnosis and treatment. These advances have led to the watch-and-wait approach, otherwise known as nonsurgical management. This review briefly outlines changes in medical and surgical treatment, advances in MRI technology and interpretation, and landmark studies or trials that have led to this exciting juncture. Herein, the authors delve into current state-of-the-art methods to assess response to treatment with MRI and endoscopy. Currently, these methods for avoiding surgery can be used to detect a complete clinical response in as many as 50% of patients with rectal cancer. Finally, the limitations of imaging and endoscopy and future challenges will be discussed.

Rectal MRI radiomics inter- and intra-reader reliability: should we worry about that?

PURPOSE

The aim of this review paper is to summarize the current literature regarding inter- and intra-reader reliability of radiomics on rectal MRI.

METHODS

Original studies examining treatment response prediction in patients with rectal cancer following neoadjuvant therapy using rectal MRI-based radiomics between January 2010 and December 2021 were identified via a PubMed/Medline search. Studies in which intra- and/or inter-reader reliability had been reported were included in this review.

RESULTS

Thirteen studies were selected, with an average number of patients of 145 (range, 20-649). All included studies evaluated T2-weighted imaging (T2WI) and/or diffusion-weighted imaging (DWI) sequences, while 3/13 (23%) also evaluated the contrast-enhanced T1-weighted imaging (T1WI) sequence. Most of the selected studies involved two readers (10/13, 77%), 6/13 (46%) studies used baseline MRI only, 1/13 (8%) study used restaging MRI only, and 6/13 (46%) used both. Segmentation was performed manually in 10/13 (77%) studies, and in a slight majority of studies (7/13, 54%), the entire tumor volume (3D VOI) was segmented, while 4/13 (31%) studies segmented the 2D ROI and 2/13 (15%) segmented both. Intraclass correlation coefficient (ICC) on intra-reader agreement varied from 0.73 to 0.93. ICC to assess inter-reader varied from 0.60 to 0.99. Overall, features obtained from baseline rectal MRI, using 3D VOI and first-order features, had higher agreement.

CONCLUSION

Based on our qualitative assessment of a small number of non-dedicated studies, there seems to be good reliability, particularly among low-order features extracted from the entire tumor volume using baseline MRI; however, direct evidence remains scarce. More targeted research in this area is required to quantitatively verify reliability, and before these novel radiomic techniques can be clinically adopted.

ACR Appropriateness Criteria® Staging of Colorectal Cancer: 2021 Update

Preoperative imaging of rectal carcinoma involves accurate assessment of the primary tumor as well as distant metastatic disease. Preoperative imaging of nonrectal colon cancer is most beneficial in identifying distant metastases, regardless of primary T or N stage. Surgical treatment remains the definitive treatment for colon cancer, while organ-sparing approach may be considered in some rectal cancer patients based on imaging obtained before and after neoadjuvant treatment. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

MRI at Restaging After Neoadjuvant Therapy for Rectal Cancer Overestimates Circumferential Resection Margin Proximity as Determined by Comparison With Whole-Mount Pathology

BACKGROUND

Current guidelines recommend restaging with MRI after neoadjuvant therapy for rectal cancer, but the accuracy of restaging MRI in estimating circumferential margin involvement requires additional clarification.

OBJECTIVE

The objective of this study was to measure the accuracy of circumferential resection margin assessment by MRI after neoadjuvant therapy and identify characteristics associated with accuracy.

DESIGN

MRI data were retrospectively analyzed for concordance with the findings of whole-mount pathology analysis of the corresponding surgical specimens. Univariate and multivariate logistic regression analyses were performed to identify characteristics associated with accuracy.

SETTING

This study was conducted at a comprehensive cancer center.

PATIENTS

Included in the study were consecutive patients who underwent total mesorectal excision for rectal cancer between January 2018 and March 2020 after receiving neoadjuvant therapy and undergoing restaging with MRI.

MAIN OUTCOME MEASURES

The primary outcome of this study included accuracy, sensitivity, specificity, and positive and negative predictive values for categorizing the circumferential resection margin as threatened; mean and paired mean differences were in proximity of the margin.

RESULTS

Of the 94 patients included in the analysis, 39 (41%) had a threatened circumferential resection margin according to MRI at restaging, but only 17 (18%) had a threatened margin based on pathology. The accuracy of MRI in identifying a threatened margin was 63.8%, with margin proximity overestimated by 0.4 cm on average. In multivariate logistic regression, anterior location of the margin and tumor proximity to the anal verge were independently associated with reduced MRI accuracy.

LIMITATIONS

A limitation was the retrospective design at a single institution.

CONCLUSIONS

The knowledge that MRI-based restaging after neoadjuvant therapy overestimates circumferential margin proximity may render some surgical radicality unnecessary and thereby help avoid the associated morbidity. With the recognition that MRI-based assessment of margin proximity may not be reliable for anterior margin and for distal tumors, radiologists may want to use greater caution in interpreting images of tumors with these characteristics and to acknowledge the uncertainty in their reports. See Video Abstract at http://links.lww.com/DCR/B814.

LA IRM EN LA REESTADIFICACIN LUEGO DE TERAPIA NEOADYUVANTE EN EL CNCER DE RECTO SOBRESTIMA LA PROXIMIDAD DEL MARGEN DE RESECCIN CIRCUNFERENCIAL SEGN LO DETERMINADO COMPARATIVAMENTE CON LA PIEZA DE ANATOMOPATOLOGA

ANTECEDENTES:Las pautas actuales recomiendan la re-estadificación por medio de la resonancia magnética luego de terapia neoadyuvante en los casos de cáncer de recto, pero la precisión de la reevaluación con la IRM para estimar el grado de implicación del margen circunferencial requiere aclaraciones adicionales.OBJETIVO:Medir el grado de exactitud en la evaluación del margen de resección circunferencial mediante resonancia magnética después de la terapia neoadyuvante e identificar las características asociadas con la precisión.DISEÑO:Se analizaron retrospectivamente los datos de resonancia magnética para determinar la concordancia entre los hallazgos del análisis de la pieza de anatamopatología y las muestras quirúrgicas correspondientes. Se realizó el análisis de regresión logística univariada y multivariada para identificar las características asociadas con la exactitud.AJUSTE:Centro oncológico integral.PACIENTES:Todos aquellos que se sometieron consecutivamente a una excisión total del mesorrecto por cáncer rectal entre Enero 2018 y Febrero 2020 luego de recibir terapia neoadyuvante y someterse a una re-estadificación por imágenes de resonancia magnética (IRM).PRINCIPALES MEDIDAS DE RESULTADO:La exactitud, la sensibilidad y especificidad; los valores predictivos positivos y negativos para categorizar el margen de resección circunferencial como amenazado; la diferencia media y las medias pareadas de proximidad a los margenes.RESULTADOS:De los 94 pacientes incluidos en el análisis, 39 (41%) tenían un margen de resección circunferencial amenazado según la resonancia magnética en la re-estadificación, pero solo 17 (18%) tenían un margen amenazado basado en la patología. La precisión de la resonancia magnética para identificar un margen amenazado fue del 63,8%, con la proximidad del margen sobreestimada en 0,4 cm en promedio. En la regresión logística multivariada, la ubicación anterior de los bordes de resección y la proximidad del tumor al margen anal se asociaron de forma independiente con la reducción en la precisión de la resonancia magnética.LIMITACIONES:Diseño retrospectivo en una institución única.CONCLUSIONES:El saber que la re-estadificación basada en la IRM, luego de terapia neoadyuvante sobreestima la proximidad de la lesión a los márgenes circunferenciales, hace innecesaria cierta radicalidad quirúrgica complementaria, lo que ayuda a evitar morbilidad asociada. Reconociendo que la evaluación de proximidad de los márgenes de resección basada en la resonancia magnética, no puede ser confiable en casos de márgenes anteriores y en casos de tumores distales. Los radiólogos recomiendan tener más precaución en la interpretación de imágenes de tumores con estas características y reconocen cierto desasosiego en sus informes. Consulte Video Resumen en http://links.lww.com/DCR/B814.

The importance of MRI for rectal cancer evaluation

Magnetic resonance imaging (MRI) has gained increasing importance in the management of rectal cancer over the last two decades. The role of MRI in patients with rectal cancer has expanded beyond the tumor-node-metastasis (TNM) system in both staging and restaging scenarios and has contributed to identifying "high" and "low" risk features that can be used to tailor and personalize patient treatment; for instance, selecting the patients for neoadjuvant chemoradiation (NCRT) before the total mesorectal excision (TME) surgery based on risk of recurrence. Among those features, the status of the circumferential resection margin (CRM), extramural vascular invasion (EMVI), and tumor deposits (TD) have stood out. Moreover, MRI also has played a role in surgical planning, especially when the tumor is located in the low rectum, when the relationship between tumor and the anal canal is important to choose the best surgical approach, and in cases of locally advanced or recurrent tumors invading adjacent pelvic organs that may require more complex surgeries such as pelvic exenteration. As approaches using organ preservation emerge, including transanal local excision and "watch-and-wait", MRI may help in the patient selection for those treatments, follow up, and detection of tumor regrowth. Additionally, potential MRI-based prognostic and predictive biomarkers, such as quantitative and semi-quantitative metrics derived from functional sequences like diffusion-weighted imaging (DWI) and dynamic contrast-enhanced (DCE), and radiomics, are under investigation. This review provides an overview of the current role of MRI in rectal cancer in staging and restaging and highlights the main areas under investigation and future perspectives.

Accuracy of MRI for predicting anterior peritoneal reflection involvement in locally advanced rectal cancer: a comparison with operative findings

PURPOSE

To assess the diagnostic accuracy of preoperative rectal MRI for anterior peritoneal reflection (APR) involvement in rectal cancer through comparison with the surgeon's operative findings.

METHODS

This retrospective study was approved by the institutional review board; informed consent was waived. We enrolled 55 consecutive patients with suspected locally advanced mid-to-upper rectal cancer. All patients underwent rectal MRI using a 3T system. APR involvement in rectal cancer was assessed radiologically using a 5-point scale by two independent board-certified abdominal radiologists. The surgeon's evaluation during surgery was regarded as the gold standard for APR involvement. The accuracy of rectal MRI in predicting APR involvement was obtained.

RESULTS

Rectal MRI showed good APR identification (rater 1, 92.7%; rater 2, 94.7%). On preoperative rectal MRI, rater 1 diagnosed 19 (34.5%) patients as having APR involvement and rater 2 diagnosed 28 (50.9%) as having APR involvement. There was moderate agreement (κ = 0.602, p < 0.001) between the two raters with regard to the evaluation of APR involvement. During surgery, the surgeon confirmed APR involvement in 13 (23.6%) patients. The sensitivity, specificity, PPV, and NPV of preoperative MRI for APR involvement were 69.2%, 76.2%, 47.4%, and 88.9%, respectively. The diagnostic accuracy of MRI for predicting APR involvement was 74.6%.

CONCLUSION

Preoperative rectal MRI provides accurate anatomical information regarding APR involvement with high conspicuity. However, MRI has relatively low sensitivity (< 70%) and a low PPV (< 50%) with regard to the assessment of APR involvement in rectal tumors. Both rater 1 and rater 2 evaluated these images as positive involvement of APR. The patient underwent laparoscopic low anterior resection after preoperative evaluation. However, during surgery, the surgeon evaluated APR involvement as negative, and the final pathologic staging was confirmed as T3.

Reduced field-of-view versus full field-of-view diffusion-weighted imaging for the evaluation of complete response to neoadjuvant chemoradiotherapy in patients with locally advanced rectal cancer

PURPOSE

To determine whether reduced field-of-view (rFOV) DWI sequences can improve image quality and diagnostic performance compared with conventional full FOV (fFOV) DWI in the prediction of complete response (CR) to neoadjuvant chemoradiotherapy (CRT) in patients with locally advanced rectal cancers.

METHODS

Between September 2015 and December 2017, seventy-three patients with locally advanced rectal cancers (≥ T3 or lymph node positive) who underwent CRT and subsequent surgery were included in this retrospective study. All patients had tumor located no more than 10 cm from the anal verge, and underwent rectal MRI including fFOV b-1000 DWI and rFOV b-1000 DWI at 3 T before and after CRT. Image quality and diagnostic performance in predicting CR were compared between rFOV DWI and fFOV DWI sets by two reviewers.

RESULTS

Based on a 12-point scale, rFOV DWI provided better image quality scores than fFOV DWI (9.1 ± 1.7 vs. 8.4 ± 1.0, respectively, P < 0.001). Diagnostic accuracy (A_z) in evaluating CR was better with the rFOV DWI set than with the fFOV DWI set for both reviewers: reviewer 1, 0.78 vs. 0.57 (P = .004); reviewer 2, 0.72 vs. 0.61 (P = .031).

CONCLUSION

rFOV DWI of rectal cancer can provide better overall image quality, and its addition to conventional rectal MRI may provide better diagnostic accuracy than fFOV DWI in the evaluation of CR to neoadjuvant CRT in patients with locally advanced rectal cancer.

Imaging Strategies for Rectal Cancer Initial Staging: Does Pelvic Computed Tomography Provide Significantly Additional Findings when High-resolution Magnetic Resonance Imaging has Been Performed?

BACKGROUND

Initial staging of rectal cancer is done by high-resolution magnetic resonance imaging (MRI), however, pelvic computed tomography (CT) is also frequently used. The aim of this study was to evaluate the added clinical benefit of pelvic CT or whether it can alter the initial staging or not.

METHODS

The study was composed of 187 patients with rectal cancer. Firstly, imaging except pelvic CT was evaluated. Secondly, the pelvic CT was evaluated and the staging was adjusted according to the new findings. Subsequently, the two staging results were compared to investigate the added clinical benefit of pelvic CT.

RESULTS

Compared with the imaging data except pelvic CT, new findings revealed by the pelvic CT included metastases of the pelvic bone (n = 1) and pelvic peritoneum (n = 3). However, the new findings did not change the primary staging. Of the three patients with pelvic peritoneal metastasis, two were already determined with peritoneal involvement and ascites by abdominal CT, and the third patient was observed with liver and distant lymph node metastasis. Thus, none of their initial stagings needed to be changed.

CONCLUSION

The addition of pelvic CT to the pre-treatment imaging strategy cannot provide added clinical benefit for the primary evaluation of rectal cancer.

Response Assessment with MRI after Chemoradiotherapy in Rectal Cancer: Current Evidences

Baseline magnetic resonance imaging (MRI) has become the primary staging modality for surgical plans and stratification of patient populations for more efficient neoadjuvant treatment. Patients who exhibit a complete response to chemoradiotherapy (CRT) may achieve excellent local tumor control and better quality of life with organ-preserving treatments such as local excision or even watch-and-wait management. Therefore, the evaluation of tumor response is a key factor for determining the appropriate treatment following CRT. Although post-CRT MRI is generally accepted as the first-choice method for evaluating treatment response after CRT, its application in the clinical decision process is not fully validated. In this review, we will discuss various oncologic treatment options from radical surgical technique to organ-preservation strategies for achieving better cancer control and improved quality of life following CRT. In addition, the current status of post-CRT MRI in restaging rectal cancer as well as the main imaging features that should be evaluated for treatment planning will also be described for the tailored treatment.

PET/MRI for Gastrointestinal Imaging: Current Clinical Status and Future Prospects

Positron emission tomography (PET)/computed tomography (CT) with 2-deoxy-2-[¹⁸F]fluoro-d-glucose (FDG) has become the standard of care for the initial staging and subsequent treatment response assessment for numerous gastrointestinal malignancies. However, it is often supplemented by magnetic resonance imaging (MRI) for local tumor staging. Hybrid PET/MRI scanners, which acquire PET data and MRI data simultaneously, have the potential to provide accurate whole-body staging in a single examination. Furthermore, to address certain limitations of FDG, many new PET tracers have been developed to probe distinctive aspects of tumor biology.

ACR Appropriateness Criteria® Pretreatment Staging of Colorectal Cancer

Colorectal cancers are common tumors in the United States and appropriate imaging is essential to direct appropriate care. Staging and treatment differs between tumors arising in the colon versus the rectum. Local staging for colon cancer is less integral to directing therapy given radical resection is often standard. Surgical options for rectal carcinoma are more varied and rely on accurate assessment of the sphincter, circumferential resection margins, and peritoneal reflection. These important anatomic landmarks are best appreciated on high-resolution imaging with transrectal ultrasound or MRI. When metastatic disease is suspected, imaging modalities that provide a global view of the body, such as CT with contrast or PET/CT may be indicated. Rectal cancer often metastasizes to the liver and so MRI of the liver with and without contrast provides accurate staging for liver metastases. This article focuses on local and distant staging and reviews the appropriateness of different imaging for both variants. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

Morphologic predictors of pathological complete response to neoadjuvant chemoradiotherapy in locally advanced rectal cancer

Purpose

To evaluate the value of morphological parameters that can be obtained conveniently by MRI for predicting pathologically complete response (pCR) in patients with rectal cancer.

Materials and Methods

A cohort of 101 patients was examined using MRI before and after Neoadjuvant chemoradiotherapy (nCRT). Morphological parameters including maximum tumor area (MTA), maximum tumor length (MTL) and maximum tumor thickness (MTT), as well as cylindrical approximated tumor volume (CATV), distance to anal verge (DTA), and the reduction rates were evaluated by two experienced readers independently.

Results

Post-nCRT MTA and MTL, reduction rates and pre-nCRT DTA were proved to be significantly different between pCR and non-pCR with the AUCs of 0.672-0.853. The sensitivity and specificity for assessing pCR were 61.1-89.9% and 59.0-80.7% respectively. No significant correlation between pre-nCRT size measurements and pCR was obtained.

Conclusion

The convenient morphological measurements may be useful for predicting pCR with moderate sensitivity and specificity. Combining these predictors with the aim of building diagnostic model should be explored.

Initial Staging of Locally Advanced Rectal Cancer and Regional Lymph Nodes: Comparison of Diffusion-Weighted MRI With 18F-FDG-PET/CT

Purpose

The aim of the study was to compare diffusion-weighted MRI (DW-MRI) parameters with ¹⁸F-FDG PET/CT in primary locally advanced rectal cancer (LARC).

Methods

From October 2012 to September 2014, 24 patients with histologically confirmed and untreated LARC (T3–T4) prospectively underwent a pelvic 1.5-T DW-MRI (b = 0 s/mm², b = 600 s/mm²) and a whole-body ¹⁸F-FDG PET/CT, before neoadjuvant therapy. The 2 examinations were performed on the same day. Two readers measured ¹⁸F-FDG SUVmax and SUVmean of the rectal tumor and of the pathological regional lymph nodes on PET/CT and compared these with minimum and mean values of the ADC (ADCmin and ADCmean) on maps generated from DW-MRI. The diagnostic performance of ADC values in identifying pathological lymph nodes was also assessed.

Results

Regarding tumors (n = 24), we found a significant negative correlation between SUVmean and corresponding ADCmean values (ρ = −0.61, P = 0.0017) and between ADCmin and SUVmax (ρ = −0.66, P = 0.0005). Regarding the lymph nodes (n = 63), there was a significant negative correlation between ADCmean and SUVmean values (ρ = −0.38, P = 0.0021), but not between ADCmin and SUVmax values (ρ = −0.11, P = 0.41). Neither ADCmean nor ADCmin values helped distinguish pathological from benign lymph nodes (AUC of 0.24 [confidence interval, 0.10–0.38] and 0.41 [confidence interval, 0.22–0.60], respectively).

Conclusions

The correlations between ADCmean and SUVmean suggest an association between tumor cellularity and metabolic activity in untreated LARC and in regional lymph nodes. However, compared with ¹⁸F-FDG PET/CT, ADC values are not reliable for identifying pathological lymph nodes.

Pre-operative staging of rectal cancer: a review of imaging techniques

INTRODUCTION

The treatment of rectal cancer has diversified in recent years, presenting the clinician and patient with increasingly challenging management decisions. At the heart of this decision-making process are two competing interests; more radical but more morbid treatments which optimize oncological outcome, and less radical treatments which preserve organs and function but may pose a greater risk of disease recurrence.

AREAS COVERED

Imaging plays a vital role informing this decision-making process, both by providing prognostic details about the cancer before the start of treatment and by updating this picture as the cancer responds or fails to respond to treatment. There is a range of available imaging modalities, each with its strengths and weaknesses. Optimizing rectal cancer treatment requires a clear understanding of the important questions that imaging needs to answer and the optimum imaging strategy. Expert Commentary: This article provides an evidence-based review of the available imaging techniques and an expert commentary on the best imaging strategy.

Beyond Histologic Staging: Emerging Imaging Strategies in Colorectal Cancer with Special Focus on Magnetic Resonance Imaging

Imaging plays an increasingly important role in the staging and management of colorectal cancer. In recent years, magnetic resonance imaging (MRI) has supplanted transrectal ultrasound as the preferred modality for the locoregional staging of rectal cancer. Furthermore, the advent of both diffusion-weighted imaging and hepatobiliary contrast agents has significantly enhanced the ability of MRI to detect colorectal liver metastases. In clinical practice, MRI routinely provides prognostic information, helps to guide surgical strategy, and determines the need for neoadjuvant therapies related to both the primary tumor and metastatic disease. Expanding on these roles for MRI, positron emission tomography (PET)/MRI is the newest clinical hybrid imaging modality and combines the metabolic information of PET with the high soft tissue contrast of MRI. The addition of PET/MRI to the clinical staging armamentarium has the potential to provide comprehensive state-of-the-art colorectal cancer staging in a single examination.

JOURNAL CLUB: Preoperative MRI Evaluation of Primary Rectal Cancer: Intrasubject Comparison With and Without Rectal Distention

OBJECTIVE

The aim of this study was to determine whether rectal distention influences the accuracy of MRI for tumor staging and for measuring of maximal extramural depth of tumor spread and distance between tumor and mesorectal fascia (MRF).

SUBJECTS AND METHODS

Fifty patients with rectal carcinoma underwent MRI before and after rectal distention. Both sets of MR images were reviewed by two radiologists. The scores for depiction of the mass (1-4 scale), T and N category, distance from normal rectal wall to MRF, maximal extramural depth of tumor spread, and distance between tumor and MRF were evaluated.

RESULTS

The visualization scores on MR images obtained with the rectum distended were significantly higher than those on images obtained without distention (90% vs 58% for score 4, p < 0.001). The accuracy of T category assessed on distended images was slightly higher than the accuracy on nondistended images (88.6% vs 84.1% for observer 1, 84.1% vs 81.8% for observer 2), but the accuracy of N category was stable. The distance between normal rectal wall and MRF was significantly less on distended images than on nondistended images (p < 0.05). However, there was no significant difference between nondistended and distended images for maximal extramural depth and distance between tumor and MRF (p > 0.05).

CONCLUSION

Rectal distention significantly improved visualization of tumors on MR images. It also improved T category assessment to some extent. Although the distance between normal rectal wall and MRF was significantly less with rectal distention than without rectal distention, maximal extramural depth and the distance between tumor and MRF did not vary significantly with or without rectal distention.

Circumferential resection margin positivity after preoperative chemoradiotherapy based on magnetic resonance imaging for locally advanced rectal cancer: implication of boost radiotherapy to the involved mesorectal fascia

OBJECTIVE

To identify patients who are at a higher risk of pathologic circumferential resection margin involvement using preoperative magnetic resonance imaging.

METHODS

Between October 2008 and November 2012, 165 patients with locally advanced rectal cancer (cT4 or cT3 with <2 mm distance from tumour to mesorectal fascia) who received preoperative chemoradiotherapy were analysed. The morphologic patterns on post-chemoradiotherapy magnetic resonance imaging were categorized into five patterns from Pattern A (most-likely negative pathologic circumferential resection margin) to Pattern E (most-likely positive pathologic circumferential resection margin). In addition, the location of mesorectal fascia involvement was classified as lateral, posterior and anterior. The diagnostic accuracy of the morphologic criteria was calculated using receiver operating characteristic curve analysis.

RESULTS

Pathologic circumferential resection margin involvement was identified in 17 patients (10.3%). The diagnostic accuracy of predicting pathologic circumferential resection margin involvement was 0.73 using the five-scale magnetic resonance imaging pattern. The sensitivity, specificity, positive predictive value and negative predictive value for predicting pathologic circumferential resection margin involvement were 76.5, 65.5, 20.3 and 96.0%, respectively, when cut-off was set between Patterns C and D. On multivariate logistic regression, the magnetic resonance imaging patterns D and E (P= 0.005) and posterior or lateral mesorectal fascia involvement (P= 0.017) were independently associated with increased probability of pathologic circumferential resection margin involvement. The rate of pathologic circumferential resection margin involvement was 30.0% when the patient had Pattern D or E with posterior or lateral mesorectal fascia involvement.

CONCLUSIONS

Patients who are at a higher risk of pathologic circumferential resection margin involvement can be identified using preoperative magnetic resonance imaging although the predictability is moderate.

MRI Risk Stratification for Tumor Relapse in Rectal Cancer Achieving Pathological Complete Remission after Neoadjuvant Chemoradiation Therapy and Curative Resection

Purpose

Rectal cancer patients achieving pCR are known to have an excellent prognosis, yet no widely accepted consensus on risk stratification and post-operative management (e.g., adjuvant therapy) has been established. This study aimed to identify magnetic resonance imaging (MRI) high-risk factors for tumor relapse in pathological complete remission (pCR) achieved by rectal cancer patients who have undergone neoadjuvant concurrent chemoradiation therapy (CRT) and curative resection.

Materials and Methods

We analyzed 88 (male/female = 55/33, median age, 59.5 years [range 34–78]) pCR-proven rectal cancer patients who had undergone pre-CRT MRI, CRT, post-CRT MRI and curative surgery between July 2005 and December 2012. Patients were observed for post-operative tumor relapse. We analyzed the pre/post-CRT MRIs for parameters including mrT stage, mesorectal fascia (mrMRF) status, tumor volume, tumor regression grade (mrTRG), nodal status (mrN), and extramural vessel invasion (mrEMVI). We performed univariate analysis and Kaplan-Meier survival analysis.

Results

Post-operative tumor relapse occurred in seven patients (8.0%, n = 7/88) between 5.7 and 50.7 (median 16.8) months. No significant relevance was observed between tumor volume, volume reduction rate, mrTRG, mrT, or mrN status. Meanwhile, positive mrMRF (P_pre-CRT = 0.018, P_pre/post-CRT = 0.006) and mrEMVI (P_pre-CRT = 0.026, P_{pre-/post-CRT} = 0.008) were associated with higher incidence of post-operative tumor relapse. Kaplan-Meier survival analysis revealed a higher risk of tumor relapse in patients with positive mrMRF (P_pre-CRT = 0.029, P_{pre-/post-CRT} = 0.009) or mrEMVI (P_pre-CRT = 0.024, P_{pre-/post-CRT} = 0.003).

Conclusion

Positive mrMRF and mrEMVI status was associated with a higher risk of post-operative tumor relapse of pCR achieved by rectal cancer patients, and therefore, can be applied for risk stratification and to individualize treatment plans.

The accuracy of MRI, endorectal ultrasonography, and computed tomography in predicting the response of locally advanced rectal cancer after preoperative therapy: A metaanalysis

BACKGROUND

To perform a metaanalysis to determine and compare the diagnostic performance of MRI, endorectal ultrasonography (ERUS), and computed tomography (CT) in predicting the response of locally advanced rectal cancer after preoperative therapy.

METHODS

All previously published articles on the role of MRI, CT, and/or ERUS in predicting the response of rectal cancer to preoperative therapy were collected. We divided the objective in 3 parts: the accuracy to assess (i) complete response, (ii) to detect T4 tumors with invasion to the circumferential resection margin (CRM), and (iii) to predict the presence of lymph node metastasis. The pooled estimates of, sensitivity, specificity, positive predictive value, negative predictive value, and accuracy were calculated using a bivariate mixed effect analysis.

RESULTS

Forty-six studies comprising 2,224 patients were included. (i) The pooled accuracy to assess complete tumor response were (a) 75% for MRI, (b) 82% for ERUS, (c) and 83% for CT. (ii) Pooled accuracy to detect T4 tumors with invasion to the CRM were (a) 88% and (b) 94% for ERUS. (iii) Pooled accuracy to predict the presence of lymph node metastasis was (a) 72% for MRI, (b) 72% for ERUS, (c) and 65% for CT.

CONCLUSION

MRI, CT, and ERUS cannot be used to predict complete response of locally advanced rectal cancer after CRT. In addition, the positive predictive value for these imaging techniques is low for the assessment of tumor invasion in the CRM. The accuracy of the modalities to predict the presence of metastatic lymph node disease is also low.

Systematic review and meta-analysis of the accuracy of MRI and endorectal ultrasound in the restaging and response assessment of rectal cancer following neoadjuvant therapy

AIM

Restaging imaging by MRI or endorectal ultrasound (ERUS) following neoadjuvant chemoradiotherapy is not routinely performed, but the assessment of response is becoming increasingly important to facilitate individualization of management.

METHOD

A search of the MEDLINE and Scopus databases was performed for studies that evaluated the accuracy of restaging of rectal cancer following neoadjuvant chemoradiotherapy with MRI or ERUS against the histopathological outcome. A systematic review of selected studies was performed. The methodological quality of studies that qualified for meta-analysis was critically assessed to identify studies suitable for inclusion in the meta-analysis.

RESULTS

Sixty-three articles were included in the systematic review. Twelve restaging MRI studies and 18 restaging ERUS studies were eligible for meta-analysis of T-stage restaging accuracy. Overall, ERUS T-stage restaging accuracy (mean [95% CI]: 65% [56-72%]) was nonsignificantly higher than MRI T-stage accuracy (52% [44-59%]). Restaging MRI is accurate at excluding circumferential resection margin involvement. Restaging MRI and ERUS were equivalent for prediction of nodal status: the accuracy of both investigations was 72% with over-staging and under-staging occurring in 10-15%.

CONCLUSION

The heterogeneity amongst restaging studies is high, limiting conclusive findings regarding their accuracies. The accuracy of restaging imaging is different for different pathological T stages and highest for T3 tumours. Morphological assessment of T- or N-stage by MRI or ERUS is currently not accurate or consistent enough for clinical application. Restaging MRI appears to have a role in excluding circumferential resection margin involvement.

Identification of locally advanced rectal cancer with low risk of local recurrence

Background

The routine application of neoadjuvant chemoradiotherapy for T3N0 rectal cancer remains controversial. The aim of this study was to use clinical, Magnetic resonance imaging, and pathological parameters to identify a subgroup of patients with low risk of local recurrence who might be precluded from neoadjuvant chemoradiotherapy.

Methods

We retrospectively reviewed a prospectively maintained database of consecutive rectal cancer patients who underwent curative resection. 166 pathologic confirmed T3N0 rectal cancer patients with tumor located 5–12cm above the anal verge and preoperative circumferential resection margin>1mm were included in analysis. The primary outcomes measured were3- and 5-year local recurrence rates.

Results

Local recurrence was demonstrated during follow-up in 5 patients; the actuarial overall 3- and 5-year local recurrence rates were 2.5% and 3.4%, respectively. Inadequate sampling of lymph nodes (≤12) was associated with higher local recurrence (P = 0.03) in this group of patients.

Conclusion

For upper and middle T3N0 rectal cancer with preoperative circumferential resection margin>1mm, local recurrence rate after total mesorectal excision is low and surgery alone may be enough for this group of patients.

MR imaging of locally advanced low rectal cancer: Relationships between imaging findings and the pathological tumor regression grade

BACKGROUND

To evaluate the relationship between MR measurements and the pathological tumor regression grade (pTRG).

METHODS

Two radiologists independently reviewed the pre- and postchemoradiation therapy (CRT) rectal MR images of 73 consecutive patients with locally advanced low rectal cancer who underwent neoadjuvant CRT and subsequent surgery and measured tumor diameter, area, signal intensity (SI). The percentage reduction rate for each parameter was calculated. The absolute SI ratio reduction rate was defined as the absolute value of the SI ratio reduction rate. The Kruskal-Wallis test and multivariate analysis were performed to assess the correlation between each parameter and the pTRG. Receiver operating characteristic (ROC) curves were plotted for predicting favorable regression outcomes (pTRG 3-4).

RESULTS

In multivariate analysis, the absolute SI ratio reduction rate was a significant predictor of pTRG for both radiologists. Area under the ROC curve (Az) values were 0.77-0.709 for diameter reduction rate, 0.757-0.694 for area, 0.652-0.648 for the SI ratio, 0.736-0.837 for the absolute SI ratio.

CONCLUSION

The absolute SI ratio reduction rate was significantly associated with pTRG and predicted favorable responses to CRT. Measurement of the diameter reduction rate is convenient and reliable in predicting favorable responses.

Simple measurements on diffusion-weighted MR imaging for assessment of complete response to neoadjuvant chemoradiotherapy in locally advanced rectal cancer

PURPOSE

To determine diagnostic performance of simple measurements on diffusion-weighted MR imaging (DWI) for assessment of complete tumour response (CR) after neoadjuvant chemoradiotherapy (CRT) in patients with locally advanced rectal cancer (LARC) by signal intensity (SI) and apparent diffusion coefficient (ADC) measurements.

MATERIALS AND METHODS

Sixty-five patients with LARC who underwent neoadjuvant CRT and subsequent surgery were included. Patients underwent pre-CRT and post-CRT 3.0 T MRI. Regions of interest of the highest brightness SI were included in the tumour volume on post-CRT DWI to calculate the SIlesion, rSI, ADClesion and rADC; diagnostic performance was compared by using the receiver operating characteristic (ROC) curves. In order to validate the accuracy and reproducibility of the current strategy, the same procedure was reproduced in 80 patients with LARC at 1.5 T MRI.

RESULTS

Areas under the ROC curve for identification of a CR, based on SIlesion, rSI, ADClesion, and rADC, respectively, were 0.86, 0.94, 0.66, and 0.71 at 3.0 T MRI, and 0.92, 0.91, 0.64, and 0.61 at 1.5 T MRI.

CONCLUSION

Post-CRT DWI SIlesion and rSI provided high diagnostic performance in assessing CR and were significantly more accurate than ADClesion, and rADC at 3.0 T MRI and 1.5 T MRI.

KEY POINTS

• Signal intensity (SI lesion ) and rSI are accurate for assessment of complete response. • rSI seems to be superior to SI lesion at 3.0 T MRI. • ADC or rADC measurements are not accurate for assessment of complete response.

Prognostic stratification by extramural depth of tumor invasion of primary rectal cancer based on the Radiological Society of North America proposal

OBJECTIVE

The purpose of this study was to investigate the diagnostic performance of MRI in stratifying tumors stage III (T3) in patients with rectal cancer by measuring the extramural depth of tumor invasion based on the Radiologic Society of North America (RSNA) proposal and to validate its role as a prognostic indicator.

MATERIALS AND METHODS

From January 2006 to July 2009, 146 patients with surgically and pathologically confirmed T3 rectal adenocarcinoma who underwent preoperative MRI were enrolled. Two blinded radiologists measured the maximum extramural depth of tumor invasion on T2-weighted images. To evaluate the diagnostic performance of MRI for stratifying subgroups, the study population was assigned into three subgroups (T3a, T3b, and T3c) according to extramural depth of tumor invasion (< 5, 5-10, and > 10 mm).To validate the role of extramural depth of tumor invasion as a prognostic indicator, Cox regression analysis was used for estimation of independent risk factors for postoperative recurrence. Three-year recurrence-free survival was evaluated by the Kaplan-Meier method with a log-rank test. Histopathologic reports were used as the reference standard.

RESULTS

The overall accuracy of MRI for stratifying subgroups was 71.2% (104/146) and 77.4% (113/146) for reviewers 1 and 2. Extramural depth of tumor invasion was an independent risk factor for 3-year recurrence-free survival (hazard ratio, 2.186; 95% CI, 1.336-3.577; p = 0.002). Kaplan-Meier curves revealed a significant difference in 3-year recurrence-free survival rates for each subgroup (86%, 69%, and 43% for T3a, T3b, and T3c; p < 0.03).

CONCLUSION

MRI can be used for prognostic stratification according to extramural depth of tumor invasion based on the RSNA proposal for patients with T3 rectal cancer.

Effectiveness of MRI for the assessment of mesorectal fascia involvement in patients with rectal cancer: a systematic review and meta-analysis

AIMS

Defining the most appropriate definition of mesorectal fascia involvement (MRF+) by reviewing literature and using new inclusion criteria to re-evaluate the effectiveness of MRI in the assessment of MRF+ for rectal cancer.

METHODS

PubMed, Medline, Embase, and the Cochrane Library databases were electronically searched from 1999 to 2012. The bivariate random effects model was used to estimate the pooled outcomes of each subgroup. The definition of MRF+ in MRI and the influence of neoadjuvant chemoradiotherapy (neo-ChRT) were especially discussed.

RESULTS

Fourteen studies involving 1,600 patients were included. Different definitions of MRF+ (≤ 1, ≤ 2 and ≤ 5 mm) in MRI exhibited different pooled sensitivity (76, 79 and 92%), specificity (88, 66 and 48%) and diagnostic odds ratio (DOR) (22.4, 6.6 and 16.0). The definition of MRF+ at ≤ 1 mm showed the highest DOR. The specificity (88 vs. 93%, p = 0.026) and DOR (15.5 vs. 39.0, p = 0.001) were lower in patients who underwent neo-ChRT than those who did not while using ≤ 1 mm as the definition of MRF+. However, the sensitivity showed no significant difference (67 vs. 74%, p = 0.129).

CONCLUSIONS

MRI is valuable for the assessment of MRF. The most appropriate definition of MRF+ in MRI is ≤ 1 mm. The effectiveness is higher in patients who did not undergo neo-ChRT.

Restaging of locally advanced rectal cancer with magnetic resonance imaging and endoluminal ultrasound after preoperative chemoradiotherapy: a systemic review and meta-analysis

BACKGROUND

Magnetic resonance imaging and endoluminal ultrasound play an important role in the restaging of locally advanced rectal cancer after preoperative chemoradiotherapy, yet their diagnostic accuracy is still controversial.

OBJECTIVE

Meta-analysis was performed to estimate the diagnostic performance of MRI and endoluminal ultrasound.

DATA SOURCES

Electronic databases from 1996 to March 2012 were searched.

STUDY SELECTION AND INTERVENTIONS

Either MRI or endoluminal ultrasound was used to restage rectal cancer after chemoradiotherapy or radiation.

MAIN OUTCOME MEASURES

T category, lymph node, and circumferential resection involvement were measured.

RESULTS

The sensitivity estimate for rectal cancer diagnosis (T0) by endoluminal ultrasound (37.0%; 95% CI, 24.0%-52.1%) was higher (p = 0.04) than the sensitivity estimate for MRI (15.3%; 95% CI, 6.5%-32.0%). For T3-4 category, sensitivity estimates of MRI and endoluminal ultrasound were comparable, 82.1% and 87.6%, whereas specificity estimates were poor (53.5% and 66.4%). For lymph node involvement, there was no significant difference between the sensitivity estimates for MRI (61.8%) and endoluminal ultrasound (49.8%). Specificity estimates for MRI and endoluminal ultrasound were 72.0% and 78.7%. For circumferential resection margin involvement, MRI sensitivity and specificity were 85.4% and 80.0%.

LIMITATIONS

To identify the heterogeneity, metaregression was performed on covariates. However, few of the covariates were identified to be statistically significant because of the lack of adequate original data.

CONCLUSION

Accurate restaging of locally advanced rectal cancer by MRI and endoluminal ultrasound is still a challenge. Identifying T0 rectal cancer by imaging is not reliable. Before performing surgery, restaging is important, but some of the T0-2 patients are likely overestimated as T3-4. Both modalities for lymph node involvement are not very good. Magnetic resonance imaging may be a good method to reassess circumferential resection margin.

Is there a benefit in using magnetic resonance imaging in the prediction of preoperative neoadjuvant therapy response in locally advanced rectal cancer?

OBJECTIVE

This meta-analysis aimed to evaluate the accuracy of magnetic resonance imaging (MRI) in predicting responses in patients with locally advanced rectal cancer after preoperative neoadjuvant therapy.

METHODS

Articles in English language relating to the accuracy of MRI for this utility were retrieved. Methodological quality was assessed by Quality Assessment of Diagnostic Accuracy Studies tool. Pooled estimation and subgroup analysis data were obtained by statistical analysis.

RESULTS

Fourteen studies involved 751 pathologically confirmed patients met the inclusion criteria. Methodological quality was relatively high. To predict histopathological response in locally advanced rectal cancer by MRI, the pooled sensitivity and specificity were 0.78 [95 % confidence intervals (CI), 0.65, 0.87] and 0.81 (95 % CI, 0.72, 0.87), respectively. Positive likelihood ratio and negative likelihood ratio were 4.1 (95 %CI, 2.9, 5.8) and 0.27 (95 % CI, 0.17, 0.43), respectively. Subgroup analysis showing that imaging was performed at 3.0 T MRI devices had higher pooled sensitivity (0.92, 95 % CI, 0.84, 1.00) than the subgroup of MRI with ≤1.5 T (0.68, 95 % CI, 0.53, 0.82) (p < 0.05).The sensitivity and specificity of T2-weighted imaging (T2WI) with diffusion-weighted imaging (DWI) were 0.92 (95 % CI, 0.81, 1.00) and 0.75 (95 % CI, 0.54, 0.95); those of T2WI alone were 0.64 (95 % CI, 0.47, 0.82) and 0.88 (95 % CI, 0.81, 0.94) (p > 0.05).

CONCLUSION

This meta-analysis indicates that MRI is an accurate tool in predicting pathologic response after preoperative therapy in patients with locally advanced rectal cancer. It is suggested to perform MRI by 3.0 T devices, which might be sensitive to identify responder. The addition of DWI to T2WI showed a non-significant improvement in sensitivity, which deserves further investigation.

Locally advanced rectal cancer: is diffusion weighted MRI helpful for the identification of complete responders (ypT0N0) after neoadjuvant chemoradiation therapy?

OBJECTIVES

To determine retrospectively the additional value of DWI-MRI toT2-MRI for predicting complete response (ypT0N0 = CR) after chemoradiation-therapy (CRT) in locally advanced rectal cancer.

METHODS

Seventy locally advanced rectal cancer patients underwent CRT followed by restaging MRI and resection. Two readers with different experience levels independently scored T2 images for CR and, in a second reading, combined T2 and DWI. A 5-point confidence-level score was used to generate ROC curves. Areas under the ROC curves (AUC) and interobserver agreement were compared for both readings. Histology served as reference standard.

RESULTS

The interobserver agreement increased after addition of DWI from 0.35 to 0.58 but the AUC improved only for the experienced reader (0.77 to 0.89, p = 0.005 vs. 0.74 to 0.70, p > 0.05). Sensitivity and NPV improved from 20-30 % to 40-70 %, respectively 88 % to 91-95 %. Specificity and PPV improved only for the experienced reader (87 to 93 % respectively 27 to 63 %).

CONCLUSION

Adding DWI to T2-MRI improves consistency between readers and has potential to improve readers' accuracy dependent on his/her experience. DWI could be of additional value, particularly in ruling out CR (high NPV), but considering the sub-optimal PPV one should be cautious about relying solely on MRI for the clinical decision to offer a wait-and-see strategy.

Patients who undergo preoperative chemoradiotherapy for locally advanced rectal cancer restaged by using diagnostic MR imaging: a systematic review and meta-analysis

PURPOSE

To obtain performance values of magnetic resonance (MR) imaging for restaging locally advanced rectal cancer after neoadjuvant treatment regarding tumor staging, nodal staging, and tumor-free circumferential resection margins (CRMs).

MATERIALS AND METHODS

MEDLINE, EMBASE, and Cochrane databases were searched for studies regarding restaging compared with a reference standard by using the terms rectal neoplasms, MR imaging, and chemotherapy. The Quality Assessment of Diagnostic Accuracy Studies tool was used, and data on imaging criteria, histopathologic criteria, and restaging were extracted. Responders were defined as positives and nonresponders, as negatives. Mean sensitivity, mean specificity, and positive and negative likelihood ratios (LRs) were determined by using a bivariate random-effects model. A positive LR greater than 5 implied moderate results for responders.

RESULTS

Thirty-three studies evaluated 1556 patients. For tumor stage, mean sensitivity was 50.4%, mean specificity was 91.2%, positive LR was 5.76, and negative LR was 0.54. Diffusion-weighted (DW) imaging showed comparable positive LR with significantly improved sensitivity (P = .01) and negative LR (P = .04). Experienced observers showed higher sensitivity (P = .01) and lower negative LR (P = .03) compared with less experienced observers. For CRM, mean sensitivity, mean specificity, positive LR, and negative LR were 76.3%, 85.9%, 5.40, and 0.28, respectively. For nodal stage per patient, mean sensitivity, mean specificity, positive LR, and negative LR were 76.5%, 59.8%, 1.90, and 0.39, respectively; and for nodal stage on a lesion basis, these values were 90.7%, 73.0%, 3.37, and 0.13, respectively.

CONCLUSION

MR imaging showed heterogeneous results of diagnostic performances for restaging rectal cancer after neoadjuvant treatment, but significantly better results were demonstrated when DW imaging was used or with experienced observers. MR imaging can also be used for evaluation of CRM staging, but nodal staging remains challenging.

ACR Appropriateness Criteria pretreatment staging of colorectal cancer

Because virtually all patients with colonic cancer will undergo some form of surgical therapy, the role of preoperative imaging is directed at determining the presence or absence of synchronous carcinomas or adenomas and local or distant metastases. In contrast, preoperative staging for rectal carcinoma has significant therapeutic implications and will direct the use of radiation therapy, surgical excision, or chemotherapy. CT of the chest, abdomen, and pelvis is recommended for the initial evaluation for the preoperative assessment of patients with colorectal carcinoma. Although the overall accuracy of CT varies directly with the stage of colorectal carcinoma, CT can accurately assess the presence of metastatic disease. MRI using endorectal coils can accurately assess the depth of bowel wall penetration of rectal carcinomas. Phased-array coils provide additional information about lymph node involvement. Adding diffusion-weighted imaging to conventional MRI yields better diagnostic accuracy than conventional MRI alone. Transrectal ultrasound can distinguish layers within the rectal wall and provides accurate assessment of the depth of tumor penetration and perirectal spread, and PET and PET/CT have been shown to alter therapy in almost one-third of patients with advanced primary rectal cancer. The ACR Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed every 2 years by a multidisciplinary expert panel. The guideline development and review include an extensive analysis of current medical literature from peer-reviewed journals and the application of a well-established consensus methodology (modified Delphi) to rate the appropriateness of imaging and treatment procedures by the panel. In those instances in which evidence is lacking or not definitive, expert opinion may be used to recommend imaging or treatment.

MR volumetric measurement of low rectal cancer helps predict tumor response and outcome after combined chemotherapy and radiation therapy

PURPOSE

To retrospectively determine whether magnetic resonance (MR) volumetry of rectal cancer is a reproducible method for predicting disease-free survival (DFS) in patients with locally advanced low or midrectal tumors who undergo combined chemotherapy and radiation therapy (CRT) before total mesorectal excision.

MATERIALS AND METHODS

The institutional review board does not require approval for the use of patient data obtained for an observational retrospective study. Fifty-eight patients were included in the study; 42 patients had low-lying tumors. Two radiologists independently measured tumor volumes before and after CRT with use of semiautomated software. The radiologists were blinded to the clinical information for each patient. The tumor volume reduction ratio, circumferential resection margin, T stage, and occurrence of downstaging were compared with the histopathologic response and DFS. The threshold of tumor volume reduction for predicting DFS was assessed with receiver operating characteristic curve analysis. DFS was estimated with the Kaplan-Meier method and compared between groups with the log-rank test.

RESULTS

The interobserver correlation coefficient between the two radiologists was 0.87 (95% confidence interval [CI]: 0.76, 0.93) for pre-CRT volumetry and 0.81 (95% CI: 0.74, 0.90) for post-CRT volumetry. A tumor volume reduction of at least 70% was significantly associated with good histologic regression (tumor regression grade [TRG], 3 or 4) (P <.0001) compared with a volume reduction rate of less than 70%. DFS was studied in 51 patients. The mean follow-up of survivors at the time of analysis was 52 months ± 20 (standard deviation). Patients with a volume reduction ratio of at least 70% had a higher DFS (P <.0001). Tumor volume reduction was an independent prognostic parameter in multivariate analysis for DFS (P = .003; 95% CI: 0.01, 0.4).

CONCLUSION

The results demonstrate that volumetric measurements are reliable markers of rectal cancer prognosis, enabling the prediction of DFS and TRG. The cutoff of 70% is an easy parameter to use as a surrogate for clinical response to predict both TRG and outcome.

Locally advanced rectal cancer: added value of diffusion-weighted MR imaging for predicting tumor clearance of the mesorectal fascia after neoadjuvant chemotherapy and radiation therapy

PURPOSE

To evaluate the added value of diffusion-weighted (DW) imaging in combination with T2-weighted magnetic resonance (MR) imaging compared with T2-weighted imaging alone for predicting tumor clearance of the mesorectal fascia (MRF) after neoadjuvant chemotherapy and radiation therapy (CRT) in patients with locally advanced rectal cancer.

MATERIALS AND METHODS

This retrospective study was approved by the institutional review board, and informed consent was waived. Forty-five patients with rectal cancer with clinically suspected MRF invasion who underwent neoadjuvant CRT and subsequent surgery were enrolled. All patients underwent pre- and post-CRT 3.0-T rectal MR imaging with DW imaging. Two observers independently reviewed a set of T2-weighted images and a combined set of T2-weighted and DW images and rated them by using a five-point scale. Diagnostic performance was evaluated for each observer with receiver operating characteristic (ROC) curve analysis. Accuracy, sensitivity, specificity, positive predictive value, and negative predictive value (NPV) were assessed. The standard of reference was histopathologic findings in the surgical specimen. Pairwise comparison of the ROC curves was used to compare diagnostic performance between the two image sets; the McNemar test was used to compare accuracy, sensitivity, and specificity.

RESULTS

The diagnostic performance (area under the ROC curve [A(z)]) with respect to MRF tumor clearance of both observers improved significantly after additional review of DW images: A(z) improved from 0.770 to 0.918 (P = .017) for observer 1 and from 0.847 to 0.960 (P = .026) for observer 2. The diagnostic accuracy of DW combined with T2-weighted imaging (observer 1, 89% [40 of 45]; observer 2, 93% [42 of 45]), sensitivity (observer 1, 94% [31 of 33]; observer 2, 97% [32 of 33]) and NPV (observer 1, 82% [nine of 11]; observer 2, 91% [10 of 11]) were significantly higher than those of T2-weighted imaging alone (accuracy: observer 1, 40% [18 of 45], P < .001; observer 2, 69% [31 of 45], P = .022; sensitivity: observer 1, 21% [seven of 33], P < .001; observer 2, 67% [22 of 33], P = .002; NPV: observer 1, 30% [11 of 37], P = .013; observer 2, 45% [nine of 20], P = .025). Interobserver agreement of confidence levels was fair for T2-weighted imaging alone (κ = 0.212) but was excellent for the combined set of DW and T2-weighted images (κ = 0.880).

CONCLUSION

Adding DW imaging to T2-weighted imaging can improve the prediction of tumor clearance in the MRF after neoadjuvant CRT compared with T2-weighted imaging alone in patients with locally advanced rectal cancer.

Magnetic resonance imaging-detected tumor response for locally advanced rectal cancer predicts survival outcomes: MERCURY experience

PURPOSE

To assess magnetic resonance imaging (MRI) and pathologic staging after neoadjuvant therapy for rectal cancer in a prospectively enrolled, multicenter study.

METHODS

In a prospective cohort study, 111 patients who had rectal cancer treated by neoadjuvant therapy were assessed for response by MRI and pathology staging by T, N and circumferential resection margin (CRM) status. Tumor regression grade (TRG) was also assessed by MRI. Overall survival (OS) was estimated by using the Kaplan-Meier product-limit method, and Cox proportional hazards models were used to determine associations between staging of good and poor responders on MRI or pathology and survival outcomes after controlling for patient characteristics.

RESULTS

On multivariate analysis, the MRI-assessed TRG (mrTRG) hazard ratios (HRs) were independently significant for survival (HR, 4.40; 95% CI, 1.65 to 11.7) and disease-free survival (DFS; HR, 3.28; 95% CI, 1.22 to 8.80). Five-year survival for poor mrTRG was 27% versus 72% (P = .001), and DFS for poor mrTRG was 31% versus 64% (P = .007). Preoperative MRI-predicted CRM independently predicted local recurrence (LR; HR, 4.25; 95% CI, 1.45 to 12.51). Five-year survival for poor post-treatment pathologic T stage (ypT) was 39% versus 76% (P = .001); DFS for the same was 38% versus 84% (P = .001); and LR for the same was 27% versus 6% (P = .018). The 5-year survival for involved pCRM was 30% versus 59% (P = .001); DFS, 28 versus 62% (P = .02); and LR, 56% versus 10% (P = .001). Pathology node status did not predict outcomes.

CONCLUSION

MRI assessment of TRG and CRM are imaging markers that predict survival outcomes for good and poor responders and provide an opportunity for the multidisciplinary team to offer additional treatment options before planning definitive surgery. Postoperative histopathology assessment of ypT and CRM but not post-treatment N status were important postsurgical predictors of outcome.

Value of diffusion-weighted imaging in the detection of viable tumour after neoadjuvant chemoradiation therapy in patients with locally advanced rectal cancer: comparison with T2 weighted and PET/CT imaging

OBJECTIVES

To evaluate the added value of diffusion-weighted imaging (DWI) in combination with T(2) weighted imaging (T2WI) compared with T2WI alone or positron emission tomography (PET)/CT for detecting viable tumour after neoadjuvant chemoradiation therapy (CRT) in patients with locally advanced rectal cancer.

METHODS

50 consecutive patients with locally advanced rectal cancer (≥T3 or lymph node positive) who underwent neoadjuvant CRT and subsequent surgery were enrolled in this retrospective study. All patients underwent 3.0 T rectal MRI and PET/CT after completing CRT. For qualitative analysis, two radiologists independently reviewed T2WI alone and DWI with T2WI over a 1-month interval. One nuclear medicine physician reviewed PET/CT images using a five-point scale. Diagnostic accuracy, sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) for detecting viable tumour were assessed. For quantitative analysis, the apparent diffusion coefficients (ADCs) of the lesions were measured and compared between the viable tumour group and non-viable tumour groups.

RESULTS

For detecting viable tumours, DWI with T2WI improved diagnostic accuracies (Reviewer 1 detected 90%; Reviewer 2, 86%) over T2WI alone (Reviewer 1 detected 76%, p=0.5; Reviewer 2, 64%, p=0.013) or PET/CT (48%, p<0.001). The sensitivity of DWI with T2WI (Reviewer 1 detected 98%; Reviewer 2, 91%) was significantly higher than those of T2WI alone (Reviewer 1 detected 77%; Reviewer 2, 64%) or PET-CT (43%, p<0.05). Only for Reviewer 2 was the NPV of DWI with T2WI (43%) significantly different from that of PET/CT (17%, p<0.05). The specificities and PPVs of DWI with T2WI were not improved over those of T2WI alone or of PET/CT (both p>0.05). The mean ADC of the viable tumour group (0.93 × 10(-3) mm(2) sc(-1)) was significantly lower than that of the non-viable tumour group (1.55 × 10(-3) mm(2) sc(-1), p<0.0001).

CONCLUSION

Adding DWI to T2WI is helpful for detecting viable tumours after neoadjuvant CRT compared with T2WI alone or PET/CT in patients with locally advanced rectal cancer.

Extended surgery and pelvic exenteration for locally advanced rectal cancer. What are the limits?

Historically, locally advanced rectal cancers with invasion of tumor into adjacent organs (T4 N1, 2 tumors) have been considered poor prognosis cancers treated with palliative intent. However with the advent of multi-modality therapy and improvement in surgical reconstructive techniques, extended resections for rectal tumors are possible with acceptable patient morbidity and excellent oncological outcomes.

Apparent diffusion coefficient for evaluating tumour response to neoadjuvant chemoradiation therapy for locally advanced rectal cancer

OBJECTIVE

To determine whether change in the apparent diffusion coefficient (ADC) before and after neoadjuvant chemoradiation therapy (CRT) for locally advanced rectal cancer (LARC) would more accurately predict pathological complete response (pCR) than analysing the pre- or post-CRT ADC individually.

METHODS

76 patients with LARC (≥ T3 or lymph node-positive) underwent pre- and post-CRT, 1.5-T diffusion-weighted imaging. A blinded radiologist measured the tumour ADCs. The three measures were compared with regard to CR and non-CR. To calculate accuracy for determining pCR, receiver-operating characteristic curve (ROC) analysis was applied to the three measures.

RESULTS

The post-CRT ADC (1.43 ± 0.10) (× 10(-3) mm(2)/s) and the percentage change (70.0 ± 23.5%) in the CR (n = 11) were significantly higher than those in the non-CR (n = 65) (1.14 ± 0.18, 30.2 ± 21.7%, respectively)(both, P < 0.0001). The pre-CRT ADC (0.85 ± 0.10) of the pCR did not differ significantly from that of the non-pCR (0.88 ± 0.14)(P = 0.4094). The post-CRT ADC showed comparable relative accuracy for determining pCR to that of the percentage change (P = 0.788). However, overall accuracy of the former (87%) was higher than that of the latter (75%) (P = 0.049).

CONCLUSION

Analyzing post-CRT ADC alone can reliably differentiate pCR from non-pCR in LARC.

Intraoperative radiotherapy for locally advanced rectal cancer

Purpose

Although intraoperative radiotherapy (IORT) is known to be a method that can reduce local recurrence in locally advanced colorectal cancer, it is not widely used. The aim of this study was to report our experience with IORT for locally advanced rectal cancer.

Methods

From 1991 to 1994, nine patients with locally advanced rectal cancer received IORT. External beam radiotherapy was given postoperatively in five patients and preoperatively in three. Seven patients received chemotherapy. IORT was done with 6-MeV or 9-MeV electrons, and 12 Gy was irradiated at the tumor bed. The median follow-up period was 84 months (range, 15 to 208 months).

Results

The median age of patients was 51 years (range, 42 to 73 years). All patients had advanced clinical T-stage (cT3/4) cancer. The overall and the disease-free survival rates were 66.7% and 66.7% at 5 years, respectively. One patient developed a local recurrence near the anastomosis site, which was out of the IORT field. Four patients died before the last follow-up; three from distant metastasis and one from secondary primary cancer. Adverse effects related to IORT did not occur.

Conclusion

Although the number of patients was small in this study, IORT is thought to be safe and effective in reducing local recurrence in locally advanced rectal cancer. However, the role of IORT should be refined in the era of preoperative radio-chemotherapy followed by total mesorectal excision.

Magnetic resonance imaging (MRI) in rectal cancer: a comprehensive review

Magnetic resonance imaging (MRI) has established itself as the primary method for local staging in patients with rectal cancer. This is due to several factors, most importantly because of the ability to assess the status of circumferential resection margin. There are several newer developments being introduced continuously, such as diffusion-weighted imaging and imaging with 3 T. Assessment of loco-regional lymph nodes has also been investigated extensively using different approaches, but more work needs to be done. Finally, evaluation of tumours during or after preoperative treatment is becoming an everyday reality. All these new aspects prompt a review of the most recent advances and opinions. In this review, a comprehensive overview of the current status of MRI in the loco-regional assessment and management of rectal cancer is presented. The findings on MRI and their accuracy are reviewed based on the most up-to-date evidence. Optimisation of MRI acquisition and relevant regional anatomy are also presented, based on published literature and our own experience.

Restaging of Rectal Cancer with MR Imaging after Concurrent Chemotherapy and Radiation Therapy

In patients with rectal cancer who have received concurrent chemotherapy and radiation therapy (CCRT) before surgery, magnetic resonance (MR) imaging has low accuracy in prediction of the pathologic stage owing to overstaging or understaging. The factors related to this problem include fibrosis, desmoplastic reaction, edema, inflammation, and viable tumor nets at a fibrotic scar from a previous tumor. Preoperative diagnosis with MR imaging of histologic variants of rectal adenocarcinoma, especially mucinous adenocarcinoma, is important because these variants tend to have a poor response to CCRT. In addition, these variants manifest with high signal intensity on T2-weighted images after CCRT; this finding makes it difficult to differentiate residual tumors from remaining mucin pools. MR volumetry and functional MR imaging may be helpful in prediction and assessment of tumor response to CCRT. Awareness of post-CCRT changes helps radiologists achieve appropriate restaging of irradiated rectal cancer with MR imaging and can lead to a reduction in understaging or overstaging. It is important to obtain and compare both pre- and post-CCRT images before interpreting the post-CCRT images.

Multimodal preoperative evaluation system in surgical decision making for rectal cancer: a randomized controlled trial

PURPOSE

Multimodal preoperative evaluation (MPE) is a novel strategy for surgical decision making, incorporating the transrectal ultrasound (TRUS), 64 multi-slice spiral computer tomography (MSCT), and serum amyloid A protein (SAA) for rectal cancer. This trial aims to determine the accuracy of MPE in preoperative staging and its role in surgical decision making for rectal cancer.

METHODS

Two hundred twenty-five participants with histologically proven rectal cancer with tumor height less than 10 cm were randomly assigned into three arms in the ratio 1:1:1. Arm A (MPE) was multimodal staged by the combination of MSCT, TRUS, and SAA. Arm B (MSCT+SAA) was staged by MSCT and SAA. Arm C (MSCT) was staged only by MSCT. The primary endpoints were the accuracy of preoperative staging and expected surgical procedures. This study is registered as an International Standard Randomised Controlled Trial, number ChiCTR-DT-00000409.

RESULTS

The analysis showed statistical difference in the accuracy of T staging between arm A and B (94.6% vs. 77.8%, P=0.003) and arm A and C (94.6% vs. 80.6%, P=0.010). Statistical difference was also observed between the accuracies of preoperative N staging between arm A and C (85.1% vs. 69.4%, P=0.023) and arm A and B (85.1% vs. 84.7%, P=0.029). Surgical decision making in arm A was more accurate than that in arm C (95.9% vs. 80.6%, P=0.001). Pathological T stage (P<0.001), N stage (P<0.001), tumor node metastasis stage (P<0.001), serum level of SAA (P=0.002), and tumor height (P=0.030) were significantly associated with final surgical procedures.

CONCLUSION

MPE is an effective strategy in preoperative staging and more accurate than other available strategies in surgical decision making for rectal cancer.