Is diffusion-weighted MRI superior to FDG-PET or FDG-PET/CT in evaluating and predicting pathological response to preoperative neoadjuvant therapy in patients with rectal cancer?

MRI VS. FDG-PET for diagnosis of response to neoadjuvant therapy in patients with locally advanced rectal cancer

Aim

In this study, we aimed to compare the diagnostic values of MRI and FDG-PET for the prediction of the response to neoadjuvant chemoradiotherapy (NACT) of patients with locally advanced Rectal cancer (RC).

Methods

Electronic databases, including PubMed, Embase, and the Cochrane library, were systematically searched through December 2021 for studies that investigated the diagnostic value of MRI and FDG-PET in the prediction of the response of patients with locally advanced RC to NACT. The quality of the included studies was assessed using QUADAS. The pooled sensitivity, specificity, positive and negative likelihood ratio (PLR and NLR), and the area under the ROC (AUC) of MRI and FDG-PET were calculated using a bivariate generalized linear mixed model, random-effects model, and hierarchical regression.

Results

A total number of 74 studies with recruited 4,105 locally advanced RC patients were included in this analysis. The pooled sensitivity, specificity, PLR, NLR, and AUC for MRI were 0.83 (95% CI: 0.77-0.88), 0.85 (95% CI: 0.79-0.89), 5.50 (95% CI: 4.11-7.35), 0.20 (95% CI: 0.14-0.27), and 0.91 (95% CI: 0.88-0.93), respectively. The summary sensitivity, specificity, PLR, NLR and AUC for FDG-PET were 0.81 (95% CI: 0.77-0.85), 0.75 (95% CI: 0.70-0.80), 3.29 (95% CI: 2.64-4.10), 0.25 (95% CI: 0.20-0.31), and 0.85 (95% CI: 0.82-0.88), respectively. Moreover, there were no significant differences between MRI and FDG-PET in sensitivity (P = 0.565), and NLR (P = 0.268), while the specificity (P = 0.006), PLR (P = 0.006), and AUC (P = 0.003) of MRI was higher than FDG-PET.

Conclusions

MRI might superior than FGD-PET for the prediction of the response of patients with locally advanced RC to NACT.

[Complete response after neoadjuvant therapy: how certain is radiology?]

The concept of total neoadjuvant therapy (TNT) means a paradigm shift in the treatment of patients with rectal cancer. In cases in which the TNT induced a complete clinical response (cCR), an organ preserving watch and wait therapy concept can now be provided more often; however, this increases the demand for imaging for the determination of cCR and in the subsequent follow-up. In this article, the performance of radiology in these scenarios will be evaluated and discussed. Magnetic resonance imaging (MRI) is the current standard for local assessment of the rectum with a high sensitivity for diagnosis and staging of rectal cancer, residual tumor and tumor recurrence. However, the certain exclusion of residual malignant tissue is still difficult, in particular the differentiation of residual scar tissue from vital residual tumor is only possible with low specificity and a moderate negative predictive value (NPV). The currently discussed criteria for the assessment of imaging have not yet been validated in large cohorts and are frequently subjective. An improvement of the diagnostic accuracy for identification of cCR in patients after TNT and for monitoring patients in watch and wait treatment concepts can certainly be achieved by the integration of MRI, endoscopy and endosonography as well as clinical parameters. This should enable for identification of patients with an incomplete response or local recurrence, in time for extended treatment to be initiated without relevant impact on the patient outcome.

Comparison of percentage changes in quantitative diffusion parameters for assessing pathological complete response to neoadjuvant therapy in locally advanced rectal cancer: a meta-analysis

PURPOSE

To evaluate and compare the diagnostic performance of percentage changes in apparent diffusion coefficient (∆ADC%) and slow diffusion coefficient (∆D%) for assessing pathological complete response (pCR) to neoadjuvant therapy in patients with locally advanced rectal cancer (LARC).

METHODS

A systematic search in PubMed, EMBASE, the Web of Science, and the Cochrane Library was performed to retrieve related original studies. For each parameter (∆ADC% and ∆D%), we pooled the sensitivity, specificity and calculated the area under summary receiver operating characteristic curve (AUROC) values. Meta-regression and subgroup analyses were performed to explore heterogeneity among the studies on ∆ADC%.

RESULTS

15 original studies (804 patients with 805 lesions, 15 studies on ∆ADC%, 4 of the studies both on ∆ADC% and ∆D%) were included. pCR was observed in 213 lesions (26.46%). For the assessment of pCR, the pooled sensitivity, specificity and AUROC of ∆ADC% were 0.83 (95% confidence intervals [CI] 0.76, 0.89), 0.74 (95% CI 0.66, 0.81), 0.87 (95% CI 0.83, 0.89), and ∆D% were 0.70 (95% CI 0.52, 0.84), 0.81 (95% CI 0.65, 0.90), 0.81 (95% CI 0.77, 0.84), respectively. In the four studies on the both metrics, ∆ADC% yielded an equivalent diagnostic performance (AUROC 0.80 [95% CI 0.76, 0.83]) to ∆D%, but lower than in the studies (n = 11) only on ∆ADC% (AUROC 0.88 [95% CI 0.85, 0.91]). Meta-regression and subgroup analyses showed no significant factors affecting heterogeneity.

CONCLUSIONS

Our meta-analysis confirms that ∆ADC% could reliably evaluate pCR in patients with LARC after neoadjuvant therapy. ∆D% may not be superior to ∆ADC%, which deserves further investigation.

Comparison of 18F-FDG PET/CT and DW-MRI in assessment of neoadjuvant radiochemotherapy response in locally advanced rectal cancer patients

OBJECTIVE

Our aim is to evaluate if different metabolic parameters obtained by ¹⁸F-FDG PET/CT and diffusion weighted magnetic resonance imaging (DW-MRI) can aid in neoadjuvant radiochemotherapy (RCT) response assessment in locally advanced rectal cancer (LARC) patients.

METHODS

Out of 20 LARC patients, who were planned to receive neoadjuvant RCT, 19 were included in this prospective study. Patients had ¹⁸F-FDG PET/CT and DW-MRI at initial staging, interim (2 weeks after onset of RCT) and after completion of RCT (post-therapy). Standardized uptake value (SUV) parameters (SUVmax, SUVmean, SUVpeak, SULpeak), metabolic tumor volume (MTV) and tumor lesion glycolysis (TLG) detected on PET images and apparent diffusion coefficient (ADC) values (for b=400 and b=1000s/mm²) obtained from DW-MRI were recorded. Postoperative tumor regression grade (TRG) was used as gold-standard, except for 2 patients who were under complete remission with non-operative management 19 months post-therapy and scored as responders.

RESULTS

On interim PET/CT, no significant difference was found among PET parameters between responders and non-responders, whereas post-therapy SUVmax, SUVpeak, MTV, SULpeak, TLG (P=0.02, P=0.014, P=0.025, P=0.007, P=0.02, respectively) and initial MTV (P=0.034) were significantly lower in responders. ADC response index (RI) was higher in responders (interim P=0.026; post-therapy: P=0.018) and ROC analysis revealed that a threshold of ADC RI>41.6% for interim MRI and >44.6% for post-therapy MRI had sensitivity and specificity of 75.0% and 90.9%, respectively.

CONCLUSIONS

While interim ¹⁸F-FDG PET/CT failed to predict therapy response during RCT, post-therapy PET could accurately differentiate responders. DW-MRI was found to be more promising in interim detection of RCT response.

3.0 T MRI IVIM-DWI for predicting the efficacy of neoadjuvant chemoradiation for locally advanced rectal cancer

Purpose

The purpose of this study was to determine the diagnostic performance of intravoxel incoherent motion (IVIM) on assessing response to neoadjuvant chemoradiation (nCRT) in patients with Locally Advanced Rectal Cancer (LARC).

Methods

50 patients with rectal cancer who underwent magnetic resonance (MR) imaging before and after nCRT, the values of pre-nCRT and post-nCRT IVIM-DWI parameters apparent diffusion coefficient (ADC), diffusion coefficient (D), false diffusion coefficient (D*), and perfusion fraction (f), together with the percentage changes (∆% parametric value) induced by nCRT were calculated. According to the patient's response to nCRT, the patients were divided into pathological complete response (pCR) and non-pCR groups, Good Response (GR) group and Poor Response (PR) group, and the above values were compared between different groups. Univariate and multiple logistic regression analysis were done to investigate the relation between different parameters and patient nCRT. Draw ROC curve according to sensitivity and specificity, and compare its diagnostic efficacy.

Results

There were no significant differences in the baseline data of 50 patients. After nCRT, the ADC and D values for LARC increased significantly (all p < 0.05). The pCR group (n = 9) had higher preD*, pref, postD*, ∆%ADC and ∆%D values than the non-pCR group (n = 41) (all p < 0.05). The GR group (n = 17) exhibited higher post D, ∆%ADC and ∆%D values than the PR group (n = 33) (all p < 0.05). From the results of Logistic regression analysis found that ∆%ADC and ∆%D were significantly correlated with patients' response to nCRT. Based on ROC analysis, ∆%D had a higher area under the curve value than ∆%ADC (p = 0.009) in discriminating the pCR from non-pCR groups.

Conclusions

IVIM-DWI technology may be helpful in identifying the pCR and GR patients to nCRT for LARC.

Is It Time to Introduce PET/CT in Rectal Cancer Guidelines?

At the moment, international guidelines for rectal cancer suggest to consider F-FDG PET/CT scan in a few conditions: (1) at disease presentation in case of suspected or proven metastatic synchronous adenocarcinoma with potentially curable M1 disease; (2) in the recurrence workup for serial carcinoembryonic antigen level elevation; (3) in the recurrence workup with metachronous metastases documented by CT, MRI, or biopsy; (4) in case of strong contraindication to IV contrast agent administration; and (5) to evaluate an equivocal finding on a contrast-enhanced CT or MRI. PET/CT is not indicated in the follow-up or surveillance of rectal cancer. On the other hand, an attentive evaluation of the literature shows that PET/CT may also be used in some circumstances with significant levels of diagnostic accuracy. This review article aims to emphasize differences between current international guidelines and scientific literature in the role of PET/CT in rectal cancer.

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.

Semiquantitative Volumetry by Sequential PET/CT May Improve Prediction of Complete Response to Neoadjuvant Chemoradiation in Patients With Distal Rectal Cancer

BACKGROUND

Previous studies using PET/CT imaging have failed to accurately identify complete responders to neoadjuvant chemoradiation among patients with rectal cancer. The use of metabolic parameters alone or imprecise delineation of baseline and residual tumor volumes may have contributed for these disappointing findings.

OBJECTIVE

The purpose of this study was to determine the accuracy of complete response identification in rectal cancer after neoadjuvant chemoradiation by sequential PET/CT imaging with a decrease in tumor metabolism and volume using optimal tumor volume delineation.

DESIGN

This was a retrospective comparison of prospectively collected data from a clinical trial (National Clinical Trial 00254683).

SETTINGS

The study was conducted at a single research center.

PATIENTS

Ninety patients with cT2-4N0-2M0 distal rectal cancer underwent sequential PET/CT at baseline and 12 weeks after neoadjuvant chemoradiation. Quantitative metabolic analysis (median and maximal standard uptake values), volumetric estimates (metabolic tumor volume), and composite estimates incorporating volume and quantitative data (total lesion glycolysis) were compared for the assessment of response to neoadjuvant chemoradiation using receiver operating characteristic curves. Individual standard uptake value thresholds were used according to response to neoadjuvant chemoradiation to match metabolic activity and optimize volume delineation.

MAIN OUTCOME MEASURES

The accuracy of complete response identification by multiple volumetric and metabolic parameters using sequential PET/CT imaging was measured.

RESULTS

Variation in total lesion glycolysis between baseline and 12-week PET/CT scans was associated with the best area under the curve (area under the curve = 0.81 (95% CI, 0.69-0.92)) when compared with standard uptake value or metabolic tumor volume for the identification of a complete responder. Patients with a ≥92% decrease in total lesion glycolysis between baseline and 12-week PET/CT scan had a 90% chance to harbor complete response.

LIMITATIONS

This study was limited by its lack of interobserver agreement analysis.

CONCLUSIONS

PET/CT scan using volume and metabolic estimates with individual standard uptake value thresholds for volume determination may provide a useful tool to predict response to neoadjuvant chemoradiation in distal rectal cancer.