Comparison of intravoxel incoherent motion and diffusion kurtosis imaging and 18- FDG PET/CT in response assessment in rectosigmoid carcinoma

OBJECTIVE

To evaluate the performance of intravoxel incoherent motion and diffusion kurtosis imaging (IVIM- DKI) in response assessment of rectosigmoid carcinoma to chemo-radiotherapy (CRT) and compare with 18-FDG PET/CT parameters.

METHODS

A total of 30 patients of recto-sigmoid cancer on CRT underwent baseline staging and follow-up with IVIM - DKI. Out of this cohort, 20 patients underwent 18-FDG PET/CT. IVIM- DKI MRI and PET/CT parameters were noted from both pre and post-chemoradiotherapy (done at 6 weeks after completion) scans. Quantitative IVIM-DKI parameters, viz. apparent (ADC) and molecular (D) diffusion coefficient, perfusion coefficient (f), and kurtosis (K) were measured from non-necrotic areas and semi-quantitative PET parameters including SUV max, SUV ratio, metabolic tumor volume (MTV), total lesion glycolysis (TLG) were also measured. All these parameters correlated with the patient's response keeping RECIST 1.1 criteria as reference standard.

RESULTS

A statistically significant increase in D and ADC with a significant decline in K was noted after therapy in the entire cohort. These changes were observed in both responders as well as non-responders. No significant differences were observed in the percentage changes of these parameters post therapy amongst both groups. Among 20 patients with follow-up PET/CT imaging, a significant decline in all parameters of primary lesion was seen post-therapy. Responders (n = 12) showed a significant decline in MTV and TLG from baseline after therapy, whereas non-responders did not show any such decline. Change in TLG (ɗ TLG), followed by ɗ MTV had the strongest correlation with a positive response. A ɗ TLG value of ≥ 54.19 carried a 79% sensitivity and 83% specificity in differentiating responders from non responders.

CONCLUSION

18-FDG PET/CT is a more accurate single modality for assessing both response and tumor burden post therapy, while ADC and D from IVIM MRI are useful adjuncts to response assessment.

Serial positron-emission tomography after induction therapy as a predictor of prognostic outcomes for patients with thymic carcinoma

PURPOSE

To investigate the role of 18F-fluorodeoxy glucose-positron emission tomography/computed tomography (FDG-PET/CT) to assess pathological response and prognosis after induction therapy in patients with thymic carcinoma.

METHODS

The subjects of this retrospective study were 18 patients with thymic carcinoma who underwent FDG-PET, before and after induction therapy. We measured the maximum standardized uptake value (SUVmax) of the tumor and analyzed the correlation between the change in SUVmax and pathological response or recurrence.

RESULTS

Induction therapy led to a reduction in both the tumor size and SUVmax in most patients. A strong correlation (Pearson coefficient = 0.90, p < 0.0001) was observed between the changes in tumor size and SUVmax. Although the SUVmax and tumor size showed no association with the pathological response, an SUVmax change > 50% predicted lower recurrence rates (p = 0.03).

CONCLUSION

Changes in the SUVmax following induction therapy may serve as a valuable predictor of recurrence in patients with thymic carcinoma. This finding highlights the potential of FDG-PET as a tool for patient monitoring and prognostication of this rare subset of carcinomas. Further studies are warranted to validate these results and standardize the FDG-PET protocols for optimal clinical use.

Predicting treatment response and survival in rectal cancer: insights from 18 FDG-PET/MRI post-neoadjuvant therapy

INTRODUCTION

Accurate identification of patients with pathologic complete response (pCR) following neoadjuvant radiochemotherapy (RCT) for locally advanced rectal cancer (LARC) is essential. 18-FDG PET/MRI provides metabolic information that complements the morphological assessment of standard MRI, potentially enhancing the differentiation between fibrotic and tumorous tissues post-treatment. This study aims to evaluate the performance of 18-FDG PET/MRI in assessing treatment response compared to standard MRI.

MATERIALS AND METHODS

A prospective study was conducted at HM Sanchinarro University Hospital, Madrid, from 2018 to 2021. Patients with LARC undergoing RCT were included and staged at diagnosis and restaged 8-12 weeks post-neoadjuvant treatment using 18-FDG PET/MRI. The primary outcome was to compare the performance of PET/MRI and standard MRI in detecting pCR and tumor regression grade (TRG) confirmed via histopathological examination. Quantitative analysis assessed the apparent diffusion coefficient (ADC) and standardized uptake value (SUV). A secondary outcome included survival analysis using the Kaplan-Meier method and Cox regression analysis for radiological and pathological prognostic markers.

RESULTS

Among 33 patients, pCR was observed in 45% (14/33). PET/MRI demonstrated sensitivity, specificity, and accuracy values of 0.88, 0.80, and 0.84, respectively, for detecting pCR, compared to 0.82, 0.50, and 0.67 for standard MRI (p < 0.001). PET/MRI accurately identified TRG stages in 72% of cases, compared to 50% for standard MRI. Post-SUV, post-ADC, and delta-ADC were the most precise PET/MRI predictors for pCR, with AUC values of 0.81, 0.75, and 0.55, respectively. Patients with mrEMVI and mrTRG showed worse disease-free survival (DFS).

CONCLUSION

18-FDG PET/MRI emerges as a promising imaging tool for predicting response to neoadjuvant treatment in rectal cancer, with superior diagnostic accuracy compared to standard MRI. Radiological findings, such as EMVI, can identify high-risk patients, offering valuable prognostic insights.

FDG-PET/MRI in colorectal cancer care: an updated systematic review

PURPOSE

Since its introduction in 2011, FDG-PET/MRI has been advocated as a useful adjunct in colorectal cancer care. However, gaps and limitations in current research remain. This systematic review aims to review the current literature to quantify the utility of FDG-PET/MRI in colorectal cancer care.

METHODS

An up-to-date review was performed on the available literature between 2000 and 2023 on PubMed, EMBASE, Medline, databases. All studies reporting on the use of FDG-PET/MRI in colorectal cancer care were analyzed. The main outcome measures were accuracy in initial staging, restaging, and detection of metastatic disease in both rectal as well as colon cancers. The secondary outcome was comparing the performance of FDG-PET/MRI versus Standard of Care Imaging (SCI). Finally, the clinical significance of FDG-PET/MRI was measured in the change in management resulting from imaging findings.

RESULTS

A total of 22 observational studies were included, accounting for 988 patients. When individually compared to current Standard of Care Imaging (SCI)-MRI pelvis for rectal cancer and thoraco-abdominal contrast CT, PET/MRI proved superior in terms of distant metastatic disease detection. This led to as much as 21.0% change in management. However, the technological limitations of PET/MRI were once again highlighted, suggesting SCI should retain its place as first-line imaging.

CONCLUSION

FDG-PET/MRI appears to be a promising adjunct in staging and restaging of colorectal cancer in carefully selected patients.

Outcomes of Postchemoradiotherapy Watch-and-Wait Strategy in Patients With Rectal Cancer: A 20-Year, Single-Center Study

BACKGROUND AND OBJECTIVES

The watch-and-wait (WW) strategy is a nonsurgical alternative for patients with rectal cancer exhibiting an excellent response to chemoradiotherapy. Studies on the WW strategy have primarily investigated 5-year oncological outcomes; few have focused on longer-term outcomes or the optimal patient selection approach for this therapeutic strategy.

METHODS

This retrospective study enrolled patients with locally advanced rectal adenocarcinoma who had achieved complete response after chemoradiotherapy. Patients who achieved pathological complete response were categorized into a control group (n = 95) and those who achieved clinical complete response and were managed using the WW strategy were categorized into a case group (n = 33). Kaplan-Meier estimates were calculated for the between-group comparison of survival.

RESULTS

The median follow-up duration was 89 months. Compared with the control group, the case group exhibited improved long-term sphincter preservation, particularly for low-lying tumors (p = 0.032), and inferior nonlocal-regrowth disease-free survival (p = 0.007). Within the case group, patients achieving a complete response by positron emission tomography exhibited 5-year survival rates similar to those achieving a complete endoscopic response.

CONCLUSION

The WW strategy is associated with improved sphincter preservation but worse nonlocal-regrowth disease-free survival. The potential of PET in patient selection for this strategy deserves further investigation.

Executive Summary of the American Radium Society on Appropriate Use Criteria for Nonoperative Management of Rectal Adenocarcinoma: Systematic Review and Guidelines

For patients with rectal cancer, the standard approach of chemotherapy, radiation therapy, and surgery (trimodality therapy) is associated with significant long-term toxicity and/or colostomy for most patients. Patient options focused on quality of life (QOL) have dramatically improved, but there remains limited guidance regarding comparative effectiveness. This systematic review and associated guidelines evaluate how various treatment strategies compare to each other in terms of oncologic outcomes and QOL. Cochrane and Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) methodology were used to search for prospective and retrospective trials and meta-analyses of adequate quality within the Ovid Medline database between January 1, 2012, and June 15, 2023. These studies informed the expert panel, which rated the appropriateness of various treatments in 6 clinical scenarios through a well-established consensus methodology (modified Delphi). The search process yielded 197 articles that advised voting. Increasing data have shown that nonoperative management (NOM) and primary surgery result in QOL benefits noted over trimodality therapy without detriment to oncologic outcomes. For patients with rectal cancer for whom total mesorectal excision would result in permanent colostomy or inadequate bowel continence, NOM was strongly recommended as usually appropriate. Restaging with tumor response assessment approximately 8 to 12 weeks after completion of radiation therapy/chemoradiation therapy was deemed a necessary component of NOM. The panel recommended active surveillance in the setting of a near-complete or complete response. In the setting of NOM, 54 to 56 Gy in 27 to 31 fractions concurrent with chemotherapy and followed by consolidation chemotherapy was recommended. The panel strongly recommends primary surgery as usually appropriate for a T3N0 high rectal tumor for which low anterior resection and adequate bowel function is possible, with adjuvant chemotherapy considered if N+. Recent data support NOM and primary surgery as important options that should be offered to eligible patients. Considering the complexity of multidisciplinary management, patients should be discussed in a multidisciplinary setting, and therapy should be tailored to individual patient goals/values.

The Predictive Role of Radiomics in Breast Cancer Patients Imaged by [18F]FDG PET: Preliminary Results from a Prospective Cohort

BACKGROUND

Recently, radiomics has emerged as a possible image-derived biomarker, predominantly stemming from retrospective analyses. We aimed to prospectively assess the predictive role of [18F]FDG-PET radiomics in breast cancer (BC).

METHODS

Patients affected by stage I-III BC eligible for neoadjuvant chemotherapy (NAC) staged with [18F]FDG-PET/CT were prospectively enrolled. The pathological response to NAC was assessed on surgical specimens. From each primary breast lesion, we extracted radiomic PET features and their predictive role with respect to pCR was assessed. Uni- and multivariate statistics were used for inference; principal component analysis (PCA) was used for dimensionality reduction.

RESULTS

We analysed 93 patients (53 HER2+ and 40 triple-negative (TNBC)). pCR was achieved in 44/93 cases (24/53 HER2+ and 20/40 TNBC). Age, molecular subtype, Ki67 percent, and stage could not predict pCR in multivariate analysis. In univariate analysis, 10 radiomic indices resulted in p < 0.1. We found that 3/22 radiomic principal components were discriminative for pCR. Using a cross-validation approach, radiomic principal components failed to discriminate pCR groups but predicted the stage (mean accuracy = 0.79 ± 0.08).

CONCLUSIONS

This study shows the potential of PET radiomics for staging purposes in BC; the possible role of radiomics in predicting the pCR response to NAC in BC needs to be further investigated.

Role of [18F]FDG-PET/CT in Evaluation of Tumor Response to Chemoradiation Therapy for Advanced Colorectal Cancer

Objectives

The objective is to evaluate the efficacy of 18F-fluorodeoxyglucose positron emission tomography (18F-FDG-PET) computed tomography (CT) in the evaluation of tumor response to preoperative/palliative chemoradiotherapy (CRT) for advanced colorectal cancer; including metastatic cancer at primary presentation and recurrent cancers with local and/or distant metastasis.

Materials and Methods

Fifty patients with advanced rectal cancer underwent two point imaging with 18 FDG PET-CT before and after 3 weeks of completion of preoperative/palliative CRT in between 2016 and 2022. Patients with locally recurrent cancer also underwent radical surgery. The assessment consisted of the evaluation of the following metabolic PET parameters: Maximum standardized uptake value (SUVmax), SUVratio, metabolic tumor volume (MTV), and total lesion glycolysis (TLG). Response was assessed among the followed patients using RECIST 1.1 criteria.

Observations and Results

There was a significant decline in the mean post therapy SUVmax and SUVratio as compared to baseline (P = 0.0001). Twenty-six out of 50 (52%) patients were classified as responders. A significant decrease in all parameters (SUVmax, SUVratio, TLG, and MTV) from baseline was observed in responders of the study when comparing with nonresponders (P < 0.05). Besides SUVmax and SUVratio, the mean posttherapy TLG was significantly reduced in responders than nonresponders (P = 0.0065).

Conclusion

PET-CT is a useful combined anatomic and functional imaging modality in monitoring tumor response to preoperative/palliative CRT in advanced rectal cancer, whether primary or recurrent, including metastatic cancers at presentation. Posttherapy SUV and TLG in particular are significantly associated with treatment response.

Role of PET/Computed Tomography in Gastric and Colorectal Malignancies

This article focuses on the role of PET/computed tomography in evaluating and managing gastric cancer and colorectal cancer. The authors start with describing the common aspects of imaging with 2-deoxy-2-18F-d-glucose, followed by tumor-specific discussions of gastric and colorectal malignancies. Finally, the authors provide a brief overview of non-FDG tracers including their potential clinical applications, and describe future directions in imaging these malignancies.

Breast Imaging Physics in Mammography (Part II)

One of the most frequently detected neoplasms in women in Italy is breast cancer, for which high-sensitivity diagnostic techniques are essential for early diagnosis in order to minimize mortality rates. As addressed in Part I of this work, we have seen how conditions such as high glandular density or limitations related to mammographic sensitivity have driven the optimization of technology and the use of increasingly advanced and specific diagnostic methodologies. While the first part focused on analyzing the use of a mammography machine from a physical and dosimetric perspective, in this paper, we will examine other techniques commonly used in breast imaging: contrast-enhanced mammography, digital breast tomosynthesis, radio imaging, and include some notes on image processing. We will also explore the differences between these various techniques to provide a comprehensive overview of breast lesion detection techniques. We will examine the strengths and weaknesses of different diagnostic modalities and observe how, with the implementation of improvements over time, increasingly effective diagnoses can be achieved.

Development and multicenter validation of a multiparametric imaging model to predict treatment response in rectal cancer

OBJECTIVES

To develop and validate a multiparametric model to predict neoadjuvant treatment response in rectal cancer at baseline using a heterogeneous multicenter MRI dataset.

METHODS

Baseline staging MRIs (T2W (T2-weighted)-MRI, diffusion-weighted imaging (DWI) / apparent diffusion coefficient (ADC)) of 509 patients (9 centres) treated with neoadjuvant chemoradiotherapy (CRT) were collected. Response was defined as (1) complete versus incomplete response, or (2) good (Mandard tumor regression grade (TRG) 1-2) versus poor response (TRG3-5). Prediction models were developed using combinations of the following variable groups: (1) Non-imaging: age/sex/tumor-location/tumor-morphology/CRT-surgery interval (2) Basic staging: cT-stage/cN-stage/mesorectal fascia involvement, derived from (2a) original staging reports, or (2b) expert re-evaluation (3) Advanced staging: variables from 2b combined with cTN-substaging/invasion depth/extramural vascular invasion/tumor length (4) Quantitative imaging: tumour volume + first-order histogram features (from T2W-MRI and DWI/ADC) Models were developed with data from 6 centers (n = 412) using logistic regression with the Least Absolute Shrinkage and Selector Operator (LASSO) feature selection, internally validated using repeated (n = 100) random hold-out validation, and externally validated using data from 3 centers (n = 97).

RESULTS

After external validation, the best model (including non-imaging and advanced staging variables) achieved an area under the curve of 0.60 (95%CI=0.48-0.72) to predict complete response and 0.65 (95%CI=0.53-0.76) to predict a good response. Quantitative variables did not improve model performance. Basic staging variables consistently achieved lower performance compared to advanced staging variables.

CONCLUSIONS

Overall model performance was moderate. Best results were obtained using advanced staging variables, highlighting the importance of good-quality staging according to current guidelines. Quantitative imaging features had no added value (in this heterogeneous dataset).

CLINICAL RELEVANCE STATEMENT

Predicting tumour response at baseline could aid in tailoring neoadjuvant therapies for rectal cancer. This study shows that image-based prediction models are promising, though are negatively affected by variations in staging quality and MRI acquisition, urging the need for harmonization.

KEY POINTS

This multicenter study combining clinical information and features derived from MRI rendered disappointing performance to predict response to neoadjuvant treatment in rectal cancer. Best results were obtained with the combination of clinical baseline information and state-of-the-art image-based staging variables, highlighting the importance of good quality staging according to current guidelines and staging templates. No added value was found for quantitative imaging features in this multicenter retrospective study. This is likely related to acquisition variations, which is a major problem for feature reproducibility and thus model generalizability.

Sense and non-sense of imaging in the era of organ preservation for rectal cancer

This review summarizes the current applications and benefits of imaging modalities for organ preservation in the treatment of rectal cancer. The concept of organ preservation in the treatment of rectal cancer has revolutionized the way rectal cancer is managed. Initially, organ preservation was limited to patients with locally advanced rectal cancer who needed neoadjuvant therapy to reduce tumor size before surgery and achieved complete response. However, neoadjuvant therapy is now increasingly utilized for smaller and less aggressive tumors to achieve primary organ preservation. Additionally, more intensive neoadjuvant strategies are employed to improve complete response rates and increase the chances of successful organ preservation. The selection of patients for organ preservation is a critical component of treatment, and imaging techniques such as digital rectal exam, endoscopy, and MRI are commonly used for this purpose. In this review, we provide an overview of what imaging modalities should be chosen and how they can aid in the selection and follow-up of patients undergoing organ-preserving strategies.

[18F]FDG-PET-Based Personalized Radiotherapy Dose Prescription

PET imaging with 2'-deoxy-2'-[18F]fluoro-D-glucose ([18F]FDG) has become one of the pillars in the management of malignant diseases. It has proven value in diagnostic workup, treatment policy, follow-up, and as prognosticator for outcome. [18F]FDG is widely available and standards have been developed for PET acquisition protocols and quantitative analyses. More recently, [18F]FDG-PET is also starting to be appreciated as a decision aid for treatment personalization. This review focuses on the potential of [18F]FDG-PET for individualized radiotherapy dose prescription. This includes dose painting, gradient dose prescription, and [18F]FDG-PET guided response-adapted dose prescription. The current status, progress, and future expectations of these developments for various tumor types are discussed.

Limits of Clinical Restaging in Detecting Responders After Neoadjuvant Therapies for Rectal Cancer

BACKGROUND

Accurate clinical restaging is required to select patients who respond to neoadjuvant chemoradiotherapy for locally advanced rectal cancer and who may benefit from an organ preservation strategy.

OBJECTIVE

The purpose of this study was to review our experience with the clinical restaging of rectal cancer after neoadjuvant therapy to assess its accuracy in detecting major and pathological complete response to treatment.

DESIGN

This was a retrospective cohort study.

SETTING

This study was conducted at 2 high-volume Italian centers for Colorectal Surgery.

PATIENTS

Data were included from all consecutive patients who underwent neoadjuvant therapy and surgery for locally advanced rectal cancer from January 2012 to July 2020. Criteria to define clinical response were no palpable mass, a superficial ulcer <2 cm (major response), or no mucosal abnormality (complete response) at endoscopy and no metastatic nodes at MRI.

MAIN OUTCOME MEASURES

The main outcome measures were sensitivity, specificity, positive predictive values, and negative predictive values of clinical restaging in detecting pathological complete response (ypT0) or major pathological response (ypT0-1) after neoadjuvant therapy.

RESULTS

A total of 333 patients were included; 81 (24.3%) had a complete response whereas 115 (34.5%) had a pathological major response. Accuracy for clinical complete response was 80.8% and for major clinical response was 72.9%. Sensitivity was low for both clinical complete response (37.5%) in detecting ypT0 and clinical major response (59.3%) in detecting ypT0-1. Positive predictive value was 68.2% for ypT0 and 60.4% for ypT0-1.

LIMITATIONS

The main limitation of the study its retrospective nature.

CONCLUSION

Accuracy of actual clinical criteria to define pathological complete response or pathological major response is poor. Failure to achieve good sensitivity and precision is a major limiting factor in the clinical setting. Current clinical assessments need to be revised to account for indications for rectal preservation after neoadjuvant chemoradiotherapy. See Video Abstract at http://links.lww.com/DCR/C63 .

LMITES DE LA REESTADIFICACIN CLNICA EN LA DETECCIN DE RESPONDEDORES DESPUS DE TERAPIAS NEOADYUVANTES PARA EL CNCER DE RECTO

ANTECEDENTES:Se requiere una nueva reestadificación clínica precisa para seleccionar pacientes que respondan a la quimiorradioterapia neoadyuvante para el cáncer de recto localmente avanzado y que puedan beneficiarse de una estrategia de preservación de órganos.OBJETIVO:El propósito de este estudio fue revisar nuestra experiencia con la reestadificación clínica del cáncer de recto después de la terapia neoadyuvante para evaluar su precisión en la detección de una respuesta patológica importante y completa al tratamiento.DISEÑO:Estudio de cohorte retrospectivo.AJUSTE:Este estudio se realizó en dos centros italianos de alto volumen para cirugía colorrectal.PACIENTES:Incluimos datos de todos los pacientes consecutivos que se sometieron a terapia neoadyuvante y cirugía por cáncer de recto localmente avanzado desde enero de 2012 hasta julio de 2020. Los criterios para definir la respuesta clínica fueron ausencia de masa palpable, úlcera superficial <2 cm (respuesta mayor) o ausencia de anomalías en la mucosa. (respuesta completa) en la endoscopia, y sin ganglios metastásicos en la resonancia magnética.PRINCIPALES MEDIDAS DE RESULTADO:Exploramos la sensibilidad, la especificidad, los valores predictivos positivos y negativos de la reestadificación clínica para detectar una respuesta patológica completa (ypT0) o mayor (ypT0-1) después de la terapia neoadyuvante.RESULTADOS:Se incluyeron 333 pacientes; 81 (24,3%) tuvieron una respuesta completa mientras que 115 (34,5%) tuvieron una respuesta patológica mayor. La precisión de la respuesta clínica completa y la respuesta clínica importante fue del 80,8 % y el 72,9 %, respectivamente. La sensibilidad fue baja tanto para la respuesta clínica completa (37,5 %) en la detección de ypT0 como para la respuesta clínica mayor (59,3 %) en la detección de ypT0-1. El valor predictivo positivo fue del 68,2 % para ypT0 y del 60,4 % para ypT0-1.LIMITACIONES:Nuestro estudio tiene como principal limitación su carácter retrospectivo.CONCLUSIÓNES:La precisión de los criterios clínicos reales para definir una respuesta patológica completa o mayor es pobre. El hecho de no lograr una buena sensibilidad y precisión es un factor limitante importante en el entorno clínico. La indicación para la preservación rectal después de la quimiorradioterapia neoadyuvante necesita una mejora de la evaluación clínica actual. Consulte Video Resumen en http://links.lww.com/DCR/C63 . (Traducción-Dr. Mauricio Santamaria ).

Baseline and early digital [ 18 F]FDG PET/CT and multiparametric MRI contain promising features to predict response to neoadjuvant therapy in locally advanced rectal cancer patients: a pilot study

OBJECTIVE

In this pilot study, we investigated the feasibility of response prediction using digital [ 18 F]FDG PET/computed tomography (CT) and multiparametric MRI before, during, and after neoadjuvant chemoradiation therapy in locally advanced rectal cancer (LARC) patients and aimed to select the most promising imaging modalities and timepoints for further investigation in a larger trial.

METHODS

Rectal cancer patients scheduled to undergo neoadjuvant chemoradiation therapy were prospectively included in this trial, and underwent multiparametric MRI and [ 18 F]FDG PET/CT before, 2 weeks into, and 6-8 weeks after chemoradiation therapy. Two groups were created based on pathological tumor regression grade, that is, good responders (TRG1-2) and poor responders (TRG3-5). Using binary logistic regression analysis with a cutoff value of P  ≤ 0.2, promising predictive features for response were selected.

RESULTS

Nineteen patients were included. Of these, 5 were good responders, and 14 were poor responders. Patient characteristics of these groups were similar at baseline. Fifty-seven features were extracted, of which 13 were found to be promising predictors of response. Baseline [T2: volume, diffusion-weighted imaging (DWI): apparent diffusion coefficient (ADC) mean, DWI: difference entropy], early response (T2: volume change, DWI: ADC mean change) and end-of-treatment presurgical evaluation MRI (T2: gray level nonuniformity, DWI: inverse difference normalized, DWI: gray level nonuniformity normalized), as well as baseline (metabolic tumor volume, total lesion glycolysis) and early response PET/CT (Δ maximum standardized uptake value, Δ peak standardized uptake value corrected for lean body mass), were promising features.

CONCLUSION

Both multiparametric MRI and [ 18 F]FDG PET/CT contain promising imaging features to predict response to neoadjuvant chemoradiotherapy in LARC patients. A future larger trial should investigate baseline, early response, and end-of-treatment presurgical evaluation MRI and baseline and early response PET/CT.

Restaging of rectal cancer with hybrid positron emission tomography magnetic resonance imaging after preoperative chemoradiotherapy

INTRODUCTION

This study determines the sensitivity and specificity of positron emission tomography/magnetic resonance imaging (PET/MRI) parameters in predicting treatment response in patients with localised rectal cancer who have undergone preoperative chemoradiotherapy (CRT).

METHOD

Patients with stage I-III adenocarcinoma of the rectum planned for preoperative CRT followed by surgery were recruited. Patients had PET/MRI scans at baseline and 6-8 weeks post-CRT. Functional MRI and PET parameters were assessed for their diagnostic accuracy for tumour regression grade (TRG). Nonparametric receiver operating characteristic analysis was employed to determine the area under the ROC curve (AUC), and the sensitivity and specificity of each quantile cut-off.

RESULTS

A total of 31 patients were recruited, of whom 20 completed study protocol. All patients included had mid or lower rectal tumours. There were 16 patients (80%) with node-positive disease at presentation. The median time to surgery was 75.5 days (range 52-106 days). Histopathological assessment revealed 20% good responders (TRG 1/2), and the remaining 80% of patients had a poor response (TRG 3/4). When predicting good responders, the AUC values for percent maximum thickness reduction and percent apparent diffusion coefficient (ADC) change were 0.82 and 0.73, respectively. A maximum thickness reduction cut-off of >47% and a percent ADC change of >20% yielded a sensitivity and specificity of 75%/95% and 75%/73%, respectively.

CONCLUSION

Parameters such as percent maximum thickness reduction and percent ADC change may be useful for predicting good responders in patients undergoing preoperative CRT for rectal cancer. Larger studies are warranted to establish the utility of PET/MRI in rectal cancer staging.

Restaging rectal cancer following neoadjuvant chemoradiotherapy

Correct tumour restaging is pivotal for identifying the most personalised surgical treatment for patients with locally advanced rectal cancer undergoing neoadjuvant therapy, and works to avoid both poor oncological outcome and overtreatment. Digital rectal examination, endoscopy, and pelvic magnetic resonance imaging are the recommended modalities for local tumour restaging, while chest and abdominal computed tomography are utilised for the assessment of distant disease. The optimal length of time between neoadjuvant treatment and restaging, in terms of both oncological safety and clinical effectiveness of treatment, remains unclear, especially for patients receiving prolonged total neoadjuvant therapy. The timely identification of patients who are radioresistant and at risk of disease progression remains challenging.

Impact of preoperative chemoradiation with higher dose intensity modulated radiotherapy on pathological complete response for locally advanced rectal cancer: a systematic review

INTRODUCTION

Neoadjuvant chemoradiation (CRT) followed by total mesorectal excision is the current standard-of-care for locally advanced UICC II-III stage rectal cancer (LARC). A pathological complete response (pCR) correlates with survival. Improvements of pCR, including dose escalation, should be explored. The aim of this explorative analysis is to assess the impact on pCR of intensity-modulated radiotherapy (IMRT) with simultaneous integrated boost (SIB).

AREAS COVERED

A literature search via PICO (Population, Intervention, Comparison, Outcome) in MEDLINE/PubMed and EMBASE and a systematic review according to PRISMA (Preferred Reporting Items for Systematic Reviews and Metanalysis) methodology were performed. Studies that reported pCR rate in patients with LARC in clinical stage T2N+M0 or cT3/4 N0/+M0 treated with preoperative CRT with SIB-IMRT/VMAT (Volumetric Modulated Arc Therapy) were included. Sixty-two studies were identified, but only eight clinical trials with a total of 311 patients were included . Median follow-up was 16-61 months. pCR reached the value of 38%. Good survival outcomes were observed with a mild toxicity profile.

EXPERT OPINION

Radiotherapy dose intensification in LARC showed a slight increase of pCR compared to historical studies. Prospective evaluations are necessary to define which patients would benefit most.

Predicting neoadjuvant chemoradiotherapy response with functional imaging and liquid biomarkers in locally advanced rectal cancer

INTRODUCTION

Non-invasive predictive quantitative biomarkers are required to guide treatment individualization in patients with locally advanced rectal cancer (LARC) in order to maximise therapeutic outcomes and minimise treatment toxicity. Magnetic resonance imaging (MRI), positron emission tomography (PET) and blood biomarkers have the potential to predict chemoradiotherapy (CRT) response in LARC.

AREAS COVERED

This review examines the value of functional imaging (MRI and PET) and liquid biomarkers (circulating tumor cells (CTCs) and circulating tumor nucleic acid (ctNA)) in the prediction of CRT response in LARC. Selected imaging and liquid biomarker studies are presented and the current status of the most promising imaging (apparent diffusion co-efficient (ADC), K^trans, SUV_max, metabolic tumor volume (MTV) and total lesion glycolysis (TLG) and liquid biomarkers (circulating tumor cells (CTCs), circulating tumor nucleic acid (ctNA)) is discussed. The potential applications of imaging and liquid biomarkers for treatment stratification and a pathway to clinical translation are presented.

EXPERT OPINION

Functional imaging and liquid biomarkers provide novel ways of predicting CRT response. The clinical and technical validation of the most promising imaging and liquid biopsy biomarkers in multi-centre studies with harmonised acquisition techniques is required. This will enable clinical trials to investigate treatment escalation or de-escalation pathways in rectal cancer.

Half-dose versus full-dose 18 F-FDG total-body PET/CT in patients with colorectal cancer

PURPOSE

The purpose of this study was to investigate image quality and lesion detectability of half-dose (1.85 MBq/kg) 18 F-fluorodeoxyglucose (FDG) total-body positron emission tomography/computed tomography (PET/CT) for colorectal cancer, full-dose (3.7 MBq/kg) 18 F-FDG serving as a reference.

METHODS

Fifty patients confirmed to have colorectal cancer who underwent total-body PET/CT with half-dose 18 F-FDG were included. Another 50 colorectal cancer patients with 3.70 MBq/kg 18 F-FDG activity were selected for the full-dose group. PET images in the half-dose group were scanned for 15 min and split into 1-, 2-, 3-, 4- and 10-min duration groups, denoted G1, G2, G3, G4 and G10, respectively. In the full-dose group, PET scanning was performed for 5 min, reconstructed with the first 0.5, 1, 2 and 5 min intervals, defined as G0.5', G1', G2' and G5', respectively. Subjective image quality was assessed with 5-point Likert scales. Objective image quality parameters included maximum standardized uptake values (SUV max) , mean standardized uptake values (SUV mean )and signal-to-noise ratio (SNR) of the liver, blood pool and muscle and SUV max and tumor-to-background ratio (TBR) of lesions.

RESULTS

In the two groups, the G3 and G2' images met clinical diagnosis requirements in terms of subjective image quality, with scores ≥3. There were no differences in terms of subjective and objective image quality between the groups (G1 and G0.5', G2 and G1', G4 and G2' and G10 and G5'). In the half-dose group, 56 colorectal lesions in 50 patients confirmed by surgical pathology were clearly visible in all groups. The number of FDG-avid lymph nodes was 37 in G1, 38 in G2 and 39 in the remaining half-dose groups. The number of missed metastatic liver lesions was 1 both in G1 and G2.

CONCLUSIONS

Total-body PET/CT with half-dose was feasible for diagnosing and staging colorectal cancer compared with full-dose 18 F-FDG PET/CT. Moreover, for half-dose total-body PET/CT, a 3-min scan duration could maintain image quality and lesion detectability.

Response Evaluation Following Radiation Therapy With 18F-FDG PET/CT: Common Variants of Radiation-Induced Changes and Potential Pitfalls

Radiation therapy (RT) is one of the cornerstones in cancer treatment and approximately half of all patients will receive some form of RT during the course of their cancer management. Response evaluation after RT and follow-up imaging with ¹⁸F-Fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography/computed tomography (PET/CT) can be complicated by RT-induced acute, chronic or consequential effects. There is a general consensus that ¹⁸F-FDG PET/CT for response evaluation should be delayed for 12 weeks after completing RT to minimize the risk of false-positive findings. Radiation-induced late side effects in normal tissue can take years to develop and eventually cause symptoms that on imaging can potentially mimic recurrent disease. Imaging findings in radiation induced injuries depend on the normal tissue included in the irradiated volume and the radiation therapy regime including the total dose delivered, dose per fraction and treatment schedule. The intent for radiation therapy should be taken in consideration when evaluating the response on imaging, that is palliative vs curative or neoadjuvant vs adjuvant RT. Imaging findings can further be distorted by altered anatomy and sequelae following surgery within the radiation field. An awareness of common PET/CT-induced changes/injuries is essential when interpreting ¹⁸F-FDG PET/CT as well as obtaining a complete medical history, as patients are occasionally scanned for an unrelated cause to previously RT treated malignancy. In addition, secondary malignancies due to carcinogenic effects of radiation exposure in long-term cancer survivors should not be overlooked. ¹⁸F-FDG PET/CT can be very useful in response evaluation and follow-up in patients treated with RT, however, variants and pitfalls are common and it is important to remember that radiation-induced injury is often a diagnosis of exclusion.

18F-FDG-PET/CT-measured parameters as potential predictors of residual disease after neoadjuvant chemoradiotherapy in patients with esophageal carcinoma

Objective

To evaluate the maximum and mean standardized uptake values, together with the metabolic tumor value and the total lesion glycolysis, at the primary tumor site, as determined by ¹⁸F-fluorodeoxyglucose positron-emission tomography/computed tomography (¹⁸F-FDG-PET/CT), performed before and after neoadjuvant chemoradiotherapy (nCRT), as predictors of residual disease (RD) in patients with esophageal cancer.

Materials and Methods

The standardized uptake values and the volumetric parameters (metabolic tumor value and total lesion glycolysis) were determined by ¹⁸F-FDG-PET/CT to identify RD in 39 patients before and after nCRT for esophageal carcinoma. We used receiver operating characteristic curves to analyze the diagnostic performance of ¹⁸F-FDG-PET/CT parameters in the definition of RD. The standard of reference was histopathological analysis of the surgical specimen.

Results

Eighteen patients (46%) presented RD after nCRT. Statistically significant areas under the curve (approximately 0.72) for predicting RD were obtained for all four of the variables evaluated after nCRT. Considering the presence of visually detectable uptake (higher than the background level) at the primary tumor site after nCRT as a positive result, we achieved a sensitivity of 94% and a specificity of 48% for the detection of RD.

Conclusion

The use of ¹⁸F-FDG-PET/CT can facilitate the detection of RD after nCRT in patients with esophageal cancer.

A multicentre cohort study assessing the utility of routine blood tests as adjuncts to identify complete responders in rectal cancer following neoadjuvant chemoradiotherapy

PURPOSE

Management of rectal cancer with a complete clinical response (cCR) to neoadjuvant chemoradiotherapy (NACRT) is controversial. Some advocate "watch and wait" programmes and organ-preserving surgery. Central to these strategies is the ability to accurately preoperatively distinguish cCR from residual disease (RD). We sought to identify if post-NACRT (preoperative) inflammatory markers act as an adjunct to MRI and endoscopy findings for distinguishing cCR from RD in rectal cancer.

METHODS

Patients from three specialist rectal cancer centres were screened for inclusion (2010-2015). For inclusion, patients were required to have completed NACRT, had a post-NACRT MRI (to assess mrTRG) and proceeded to total mesorectal excision (TME). Endoluminal response was assessed on endoscopy at 6-8 weeks post-NACRT. Pathological response to therapy was calculated using a three-point tumour regression grade system (TRG1-3). Neutrophil-lymphocyte ratio (NLR), platelet-lymphocyte ratio (PLR), serum albumin (SAL), CEA and CA19-9 levels post-NACRT (preoperatively) were recorded. Variables were compared between those who had RD on post-operative pathology and those with ypCR. Statistical analysis was performed using SPSS (version 21).

RESULTS

Six hundred forty-six patients were screened, of which 422 were suitable for inclusion. A cCR rate of 25.5% (n = 123) was observed. Sixty patients who achieved cCR were excluded from final analysis as they underwent organ-preserving surgery (local excision) leaving 63 ypCR patients compared to 359 with RD. On multivariate analysis, combining cCR on MRI and endoscopy with NLR < 5 demonstrated the greatest odds of ypCR on final histological assessment [OR 6.503 (1.594-11.652]) p < 0.001]. This method had the best diagnostic accuracy (AUC = 0.962 95% CI 0.936-0.987), compared to MRI (AUC = 0.711 95% CI 0.650-0.773) or endoscopy (AUC = 0.857 95% CI 0.811-0.902) alone or used together (AUC = 0.926 95% CI 0.892-0.961).

CONCLUSION

Combining post-NACRT inflammatory markers with restaging MRI and endoscopy findings adds another avenue to aid distinguishing RD from cCR in rectal cancer.

Changes in treatment intent and target definition for preoperative radiotherapy after 18F-Fluorodeoxyglucose positron emission tomography in rectal cancer: A Meta-analysis

PURPOSE

To evaluate the impact of ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography (PET) on changes in treatment plan and target definition for preoperative radiotherapy in patients with rectal cancer.

METHODS

Embase, PubMed, and Cochrane Library were searched up to November 2020 for all studies investigating the role of preoperative FDG PET in patients who underwent neoadjuvant radiotherapy before curative-intent surgery. The proportion of patients whose treatment plan (curative vs. palliative intent) or target definition was changed after FDG PET was analyzed. A random-effects model was used for pooled analysis. The change in target definition was compared between conventional radiological imaging-based target volume [gross tumor volume (GTV) or planning target volume (PTV)] and PET-based target volume (GTV or PTV) using the standardized mean difference (SMD) and 95% confidence interval (CI).

RESULTS

A total of 336 patients from twelve studies were included. In eight studies, PET changed either the treatment intent or target definition in 24.8% of patients (95% CI 15.1% to 37.9%, I² = 69%). In ten studies, the PET-based GTV was lower than the conventional imaging-based target volume (SMD -7.0, 95% CI -1.39 to -0.01). However, there was no significant difference between conventional imaging-based and PET-based PTV (SMD -0.07, 95% CI -0.75 to 0.62). In six studies evaluating the initial staging based on PET, the initial staging (nodal or metastasis status) was changed in 53 of 229 patients (23.1%). Newly detected or additional distant metastases were identified in 22 patients (9.6%) after FDG PET.

CONCLUSION

The use of FDG PET influences radiotherapy planning in a fourth of patients with rectal cancer. FDG PET can provide additive information for accurate tumor delineation, although PET-based PTV did not significantly change. These findings suggest that FDG PET may be beneficial to patients with rectal cancer before establishing a radiotherapy plan.

Current State of Neoadjuvant Radiotherapy for Rectal Cancer

Colorectal cancer is the third most commonly diagnosed cancer, with rectal cancer accounting for 30% of cases. The current standard of care curative treatment for locally advanced rectal cancer is (chemo)radiotherapy followed by surgery and adjuvant chemotherapy. Although neoadjuvant radiotherapy has reduced the risk of local recurrence to less than 10%, the risk of distant metastasis remained high at 30% affecting patient survival. In addition, there is a recognition that there is heterogeneity in tumor biology and treatment response with good responders potentially suitable for treatment de-escalation. Therefore, new treatment sequencing and regimens were investigated. Here, we reviewed the evidence for current neoadjuvant treatment options in patients with locally advanced rectal adenocarcinoma, and highlight the new challenges in this new treatment landscape.

Direct comparison of F-18 FDG PET/CT and MRI to predict pathologic response to neoadjuvant treatment in locally advanced rectal cancer: a meta-analysis

OBJECTIVE

The purpose of the current study was to compare the diagnostic accuracies of F-18 FDG PET/CT and MRI for prediction of pathologic responses to neoadjuvant treatment (NAT) in locally advanced rectal cancer (LARC) patients based on a systematic review and meta-analyses.

METHODS

The PubMed, Cochrane, and Embase databases were searched to identify studies that conducted direct comparisons of the diagnostic performance of F-18 FDG PET/CT and MRI for the prediction of pathologic response to NAT in patients with LARC from the earliest available date of indexing up to July 31, 2020. We determined the sensitivities and specificities across studies, calculated positive and negative likelihood ratios (LR + and LR -), and we constructed summary receiver operating characteristic curves.

RESULTS

In nine studies (427 patients), the pooled sensitivity of F-18 FDG PET/CT was 0.79 (95% CI 0.71-0.86) and the pooled specificity was 0.74 (95% CI 0.60-0.84). LR syntheses yielded an overall LR + of 3.1 (95% CI 1.9-5.0) and an LR - of 0.28 (95% CI 0.18-0.43). The pooled diagnostic odds ratio (DOR) was 11 (95% CI 5-26). The pooled sensitivity of MRI was 0.89 (95% CI 0.77-0.95) and the pooled specificity was 0.66 (95% CI 0.55-0.76). LR syntheses yielded an overall LR + of 2.6 (95% CI 1.9-3.6) and an LR - of 0.17 (95% CI 0.08-0.37). The pooled DOR was 15 (95% CI 6-42). In meta-regression analysis, no variable was identified as the source of the study heterogeneity.

CONCLUSION

F-18 FDG PET/CT and MRI showed similar diagnostic performances for the prediction of pathologic responses to NAT in patients with LARC. However, each modality can be a complement to other rather than being used singly.

Variants and Pitfalls in PET/CT Imaging of Gastrointestinal Cancers

In the past two decades, PET/CT has become an essential modality in oncology increasingly used in the management of gastrointestinal (GI) cancers. Most PET/CT tracers used in clinical practice show some degree of GI uptake. This uptake is quite variable and knowledge of common patterns of biodistribution of various radiotracers is helpful in clinical practice. 18F-Fluoro-Deoxy-Glucose (FDG) is the most commonly used radiotracer and has quite a variable uptake within the bowel. 68Ga-Prostate specific membrane antigen (PSMA) shows intense uptake within the proximal small bowel loops. 11C-methyl-L-methionine (MET) shows high accumulation within the bowels, which makes it difficult to assess bowel or pelvic diseases. One must also be aware of technical artifacts causing difficulties in interpretations, such as high attenuation oral contrast material within the bowel lumen or misregistration artifact due to patient movements. It is imperative to know the common variants and benign diseases that can mimic malignant pathologies. Intense FDG uptake within the esophagus and stomach may be a normal variant or may be associated with benign conditions such as esophagitis, reflux disease, or gastritis. Metformin can cause diffuse intense uptake throughout the bowel loops. Intense physiologic uptake can also be seen within the anal canal. Segmental bowel uptake can be seen in inflammatory bowel disease, radiation, or medication induced enteritis/colitis or infection. Diagnosis of appendicitis or diverticular disease requires CT correlation, as normal appendix or diverticulum can show intense uptake. Certain malignant pathologies are known to have only low FDG uptake, such as early-stage esophageal adenocarcinoma, mucinous tumors, indolent lymphomas, and multicystic mesotheliomas. Response assessment, particularly in the neoadjuvant setting, can be limited by post-treatment inflammatory changes. Post-operative complications such as abscess or fistula formation can also show intense uptake and may obscure underlying malignant pathology. In the absence of clinical suspicion or rising tumor marker, the role of FDG PET/CT in routine surveillance of patients with GI malignancy is not clear.

Tumor Volume as Predictor of Pathologic Complete Response Following Neoadjuvant Chemoradiation in Locally Advanced Rectal Cancer

PURPOSE

Neoadjuvant chemoradiation followed by surgery is the current standard of care in the treatment of locally advanced rectal cancer. Those who achieved pathologic complete response, following this standard of care, complete pathologic response (pCR) had better outcome. Until now there are no reliable clinical parameters to predict this response. The purpose of the study was to evaluate whether tumor volume may serve as a predictive factor in patients treated with neoadjuvant chemoradiotherapy.

MATERIALS AND METHODS

Between September 2015 and September 2019, patients diagnosed with stage IIA to IIIC rectal adenocarcinoma, who were treated with neoadjuvant chemoradiation, were enrolled to this study. All patients underwent rectal ultrasound, pelvic magnetic resonance imaging, fluorodeoxyglucose-positron emission tomography-computed tomography and the diagnosis was confirmed by pathology report. Radiation therapy was consisted of 50 Gy delivered to the tumor site, 2 Gy a day, 5 times a week and to the pelvic lymph nodes for a total of 45 Gy in 1.8 Gy a day, 5 times a week. The gross tumor volume (GTV) was contoured by radiation oncology expert, reviewed by radiology and nuclear medicine expert and approved by radiation therapy tumor board. Chemotherapy was consisted of either capecitabine 875 mg/m2 twice a day or continuous. IV infusion of 5 fluorouracil 375 mg/m2 for 4 consecutive days in a 3 weeks apart. Operation, either low anterior or abdominoperineal resection was carried out 6 to 8 weeks following completion of treatment. Patients were assigned to either complete pathologic response (pCR) or non-pCR groups. GTV, among other clinical and treatment parameters, were evaluated for prediction of pCR. Statistical methods included independent t test, logistic regression, area under the curve-receiver operating characteristic, Bayesian independent statistics and multilayer perceptron model.

RESULTS

One hundred ninety-three patients were enrolled to this study, 6 were excluded due to metastatic disease detected at the time of operation. Seventy had stage II and 117 had stage III. Forty-four of 187 (23.5%) patients achieved pCR and 143 patients had either partial or no response/progressive disease. Among the 44 pCR group, 21 had stage II and 23 had stage III disease. Treatment interruption, defined as either a delay of up to 1 week in radiation, and a dose reduction to 75%, was occurred in 42 patients. Sex, ethnicity, distance from anal verge to tumor, height, weight, age, delivered radiation dose, radiotherapy techniques, clinical T and N stage and GTV were evaluated for prediction of pCR. GTV at the volume of <39.5 cm3 was the only significant predictive factor to detect pCR by logistic regression model (P<0.01) and by Bayesian independent test (P=0.026). Area under the receiver operating characteristic curve of GTV <39.5 cm3 showed area under the curve of 0.715 (P=0.009) for stage II and area under the curve of 0.62 (P>0.05) for stage III.

CONCLUSION

GTV may serve as a predictive factor for achieving pCR in locally advanced rectal cancer after neoadjuvant chemoradiotherapy.

T2-weighted, apparent diffusion coefficient and 18F-FDG PET histogram analysis of rectal cancer after preoperative chemoradiotherapy

Background

The aim of our study was to investigate the correlation among T2-weighted (T2w) images, apparent diffusion coefficient (ADC) maps, ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography (PET) images, histogram analysis and the pathological response in locally advanced rectal cancer (LARC) after preoperative chemoradiotherapy (pCRT).

Methods

Patients with LARC were prospectively enrolled between February 2015 and August 2018 and underwent PET/magnetic resonance imaging (MRI). MRI included T2w and diffusion-weighted imaging (DWI)-sequences. ADC maps and PET images were matched to the T2w images. Voxel-based standardized uptake values (SUVs,) ADC and T2w-signal-intensity values were collected from the volumes of interest (VOIs) and mean, skewness and kurtosis were calculated. Spearman’s correlation coefficient was applied to evaluate the correlation among the variables and tumor regression grade (TRG), T stage, N stage and fibrosis.

Results

Twenty-two patients with biopsy-proven LARC in the low or mid rectum were enrolled [17 males, mean age was 69 years (range 49–85 years)]. Seven patients experienced complete regression (TRG1). A significant positive correlation was found between SUV mean values (ρ = 0.480; p = 0.037) and TRG. No other significant correlations were found.

Conclusions

Histogram analysis of SUV values is a predictor of TRG in LARC.

[18F]FDG PET/MRI in rectal cancer

We conducted a systematic literature review on the use of [18F]FDG PET/MRI for staging/restaging rectal cancer patients with PubMed, Scopus, and Web of Science, based on the PRISMA criteria. Three authors screened all titles and abstracts and examined the full texts of all the identified relevant articles. Studies containing aggregated or duplicated data, review articles, case reports, editorials, and letters were excluded. Ten reports met the inclusion criteria. Four studies examined T staging and one focused on local recurrences after surgery; the reported sensitivity (94-100%), specificity (73-94%), and accuracy (92-100%) varied only slightly from one study to another. The sensitivity, specificity, and accuracy of [18F]FDG PET/MRI for N staging were 90-93%, 92-94%, and 42-92%. [18F]FDG PET/MRI detected malignant nodes better than MRI, resulting in treatment change. For M staging, [18F]FDG PET/MRI outperformed [18F]FDG PET/CT and CT in detecting liver metastases, whereas it performed worse for lung metastases. The results of this review suggest that [18F]FDG PET/MRI should be used for rectal cancer restaging after chemoradiotherapy and to select patients for rectum-sparing approaches thanks to its accuracy in T and N staging. For M staging, it should be associated at least with a chest CT scan to rule out lung metastases.

Feasibility of MRI Radiomics for Predicting KRAS Mutation in Rectal Cancer

The mutation status of KRAS is a significant biomarker in the prognosis of rectal cancer. This study investigated the feasibility of MRI-based radiomics in predicting the mutation status of KRAS with a composite index which could be an important criterion for KRAS mutation in clinical practice. In this retrospective study, a total of 127 patients with rectal cancer were enrolled. The 3D Slicer was used to extract the radiomics features from the MRI images, and sparse support vector machine (SVM) with linear kernel was applied for feature reduction. The radiomics classifier for predicting the KRAS status was then constructed by Linear Discriminant Analysis (LDA) and its performance was evaluated. The composite index was determined with LDA model. Out of 127 rectal cancer subjects, there were 44 KRAS mutation cases and 83 wild cases. A total of 104 radiomics features were extracted, 54 features were filtered by linear SVM with L1-norm regularization and 6 features that had no significant correlations within them were finally selected. The radiomics classifier constructed using the 6 features featured an AUC value of 0.669 (specificity: 0.506; sensitivity: 0.773) with LDA. Furthermore, the composite index (Radscore) had statistically significant difference between the KRAS mutation and wild groups. It is suggested that the MRI-based radiomics has the potential in predicting the KRAS status in patients with rectal cancer, which may enhance the diagnostic value of MRI in rectal cancer.

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.

Recent advances of PET imaging in clinical radiation oncology

Radiotherapy and radiation oncology play a key role in the clinical management of patients suffering from oncological diseases. In clinical routine, anatomic imaging such as contrast-enhanced CT and MRI are widely available and are usually used to improve the target volume delineation for subsequent radiotherapy. Moreover, these modalities are also used for treatment monitoring after radiotherapy. However, some diagnostic questions cannot be sufficiently addressed by the mere use standard morphological imaging. Therefore, positron emission tomography (PET) imaging gains increasing clinical significance in the management of oncological patients undergoing radiotherapy, as PET allows the visualization and quantification of tumoral features on a molecular level beyond the mere morphological extent shown by conventional imaging, such as tumor metabolism or receptor expression. The tumor metabolism or receptor expression information derived from PET can be used as tool for visualization of tumor extent, for assessing response during and after therapy, for prediction of patterns of failure and for definition of the volume in need of dose-escalation. This review focuses on recent and current advances of PET imaging within the field of clinical radiotherapy / radiation oncology in several oncological entities (neuro-oncology, head & neck cancer, lung cancer, gastrointestinal tumors and prostate cancer) with particular emphasis on radiotherapy planning, response assessment after radiotherapy and prognostication.

Clinical impact of FDG PET/CT in alimentary tract malignancies: an updated review

The use of ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography combined with computed tomography (PET/CT) is well established in the evaluation of alimentary tract malignancies. This review of the literature and demonstration of correlative images focuses on the current role of PET/CT in the diagnosis (including pathologic/clinical staging) and post-therapy follow-up of esophageal, gastric, and colorectal cancers. PET/CT provides utility in the management of esophageal cancer, including detection of distant disease prior to resection. In gastric cancer, PET/CT is useful in detecting solid organ metastases and in characterizing responders vs. non-responders after neoadjuvant chemotherapy, the latter of which have poorer overall survival. In patients with GIST tumors, PET/CT also determines response to imatinib therapy with greater expedience as compared to CECT. For colorectal cancer, PET/CT has proven helpful in detecting hepatic and other distant metastases, treatment response, and differentiating post-radiation changes from tumor recurrence. Our review also highlights several pitfalls in PET/CT interpretation of alimentary tract lesions.

Imaging and Management of Rectal Cancer

High-resolution phased array external magnetic resonance imaging (MRI) is the first investigation of choice in rectal cancer for local staging, both in the primary and restaging situations. Use of MRI helps differentiate between those with good prognosis, which can be offered upfront surgery and the poor prognostic cases where treatment intensification is needed. MRI identified poor prognostic factors are threatened or involved mesorectal fascia, T3 tumors with >5 mm extramural spread, those with extramural vascular invasion, pelvic sidewall nodes and mucinous tumors. At restaging, use of MRI helps evaluate response and an MR tumor regression grading system is being evaluated. Complete response seen on clinical examination and endoscopy, needs confirmation on MRI using both T2-weighted and diffusion-weighted sequences to justify a "watch and wait" approach. In this subset of patients, MRI also plays a role in monitoring and detecting early regrowth. In those with partial response, MRI helps define surgical margins and can be used as a roadmap to decide between sphincter preserving surgeries and radical sphincter sacrificing surgeries; pelvic exenteration and pelvic sidewall lymph node dissection. Poor responders on MRI may benefit from adjuvant chemotherapy. Use of MRI thus helps in individualizing treatment in rectal cancer.

18F-FDG PET/MRI for Rectal Cancer TNM Restaging After Preoperative Chemoradiotherapy: Initial Experience

OBJECTIVE

F-FDG-PET/MRI is a novel hybrid techinque that has been recently introduced in oncological imaging, showing promising results. The aim of this study is to assess the value of whole-body F-FDG-PET/MRI for predicting the pathological stage of locally advanced rectal cancer after preoperative chemoradiotherapy.

DESIGN

This was a prospective observational study.

SETTINGS

The study was conducted at a tertiary care hospital.

PATIENTS

Thirty-six patients with locally advanced rectal cancer (25 male, median age 68.5 years) were prospectively assessed with PET/MRI and thoracoabdominal CT before and after preoperative chemoradiotherapy. Twenty-seven patients underwent low anterior or abdominoperineal resection. Nine patients with a complete clinical response underwent organ-preserving treatment (8 local excision and 1 watch-and-wait approach) with >1-year follow-up.

MAIN OUTCOME MEASURES

One radiologist evaluated pelvic MRI and CT. A second radiologist and a nuclear medicine physician jointly assessed PET/MRI. The imaging was compared with histology or follow-up (ypT0 vs T ≥1 and ypN0 vs ypN+ categories). Metastases were confirmed with biopsy or a follow-up CT scan at least at 1 year after preoperative chemoradiotherapy. The sensitivity, specificity, and accuracy values of the imaging techniques were calculated using standard formulas.

RESULTS

The accuracy for ypT staging was 89% and 92%, and the accuracy for ypN was 86% and 92% for MRI and PET/MRI. Compared with CT, PET/MRI correctly diagnosed 4 of 5 metastases, but it did not detect a lung metastatic nodule. In 11% of the patients, the PET/MRI changed the treatment strategy.

LIMITATIONS

This study is limited by its small sample size.

CONCLUSIONS

Although the whole-body PET/MRI was more accurate than the pelvic MRI alone for the prediction of tumor and node response to preoperative chemoradiotherapy, the technique performed worse than CT in detecting small lung metastasis. See Video Abstract at http://links.lww.com/DCR/B108. TOMOGRAFÍA POR EMISIÓN DE POSITRONES DE 18F- FLUORODEOXIGLUCOSA (FDG) / RESONANCIA MAGNÉTICA (TEP/RM) PARA ESTADIFICACIÓN TUMORAL TNM DE CÁNCER DEL RECTO DESPUÉS DE LA QUIMIORRADIOTERAPIA PREOPERATORIA - EXPERIENCIA INICIAL: Evaluar el valor de la tomografía por emisión de positrones de 18F-fluorodeoxiglucosa / resonancia magnética (TEP/RM) para predecir el estadio patológico del cáncer de recto localmente avanzado después de la quimiorradioterapia preoperatoria.Este fue un estudio prospectivo observacional.El estudio se realizó en un hospital de atención terciaria.Treinta y seis pacientes con cáncer rectal localmente avanzado (25 hombres, edad media de 68.5 años) fueron evaluados prospectivamente con TEP/RM y tomografía computarizada (TC) toraco-abdominal antes y después de la quimiorradioterapia preoperatoria. Veintisiete pacientes se sometieron a resección anterior baja o abdominoperineal. Nueve pacientes con una respuesta clínica completa se sometieron a un tratamiento de preservación de órganos (8 escisión local y 1 un enfoque de observar y esperar) con un seguimiento de> 1 año.Un radiólogo evaluó la RM pélvica y la TC. Un segundo radiólogo y un médico de medicina nuclear evaluaron conjuntamente TEP / RM. La imagen se comparó con la histología o el seguimiento (ypT0 vs T ≥1 y ypN0 vs ypN + categorías). Las metástasis se confirmaron con biopsia o una TC de seguimiento al menos 1 año después de la quimiorradioterapia preoperatoria. Los valores de sensibilidad, especificidad y precisión de las técnicas de imagen se calcularon utilizando fórmulas estándar.La precisión para la estadificación ypT fue del 89% y 92%, y la precisión para ypN fue del 86% y 92% para RM y TEP/RM respectivamente. En comparación con la TC, la TEP / RM diagnosticó correctamente 4 de 5 metástasis, pero no detectó un nódulo metastásico pulmonar. En el 11% de los pacientes, la TEP / RM cambió la estrategia de tratamiento.Este estudio está limitado por su pequeño tamaño de muestra.Si bien la TEP / RM de todo el cuerpo fue más precisa que la RM pélvica sola para la predicción de la respuesta tumoral y ganglionar a la quimiorradioterapia preoperatoria, la técnica funcionó peor que la TC para detectar metástasis pulmonares pequeños. Consulte Video Resumen en http://links.lww.com/DCR/B108.

FDG PET Hybrid Imaging

Molecular imaging with positron emission tomography (PET) using tumour-seeking radiopharmaceuticals has gained wide acceptance in oncology with many clinical applications. The hybrid imaging modality PET/CT (computed tomography) allows assessing molecular as well as morphologic information at the same time. Therefore, PET/CT represents an efficient tool for whole-body staging and re-staging within one imaging modality. In oncology, the glucose analogue 18-F-fluorodeoxyglucose (FDG) is the most widely used PET/CT radiopharmaceutical in clinical routine. FDG PET and FDG PET/CT have been used for staging and re-staging of tumour patients in numerous studies. This chapter will discuss the use and the main indications of FDG PET/CT in oncology with special emphasis on lung cancer, lymphoma, head and neck cancer, melanoma and breast cancer (among other tumour entities). A review of the current literature is given with respect to primary diagnosis, staging and diagnosis of recurrent disease. Besides its integral role in diagnosis, staging and re-staging of disease in oncology, there is increasing evidence that FDG PET/CT can be used for therapy response assessment (possibly influencing therapeutic management and treatment planning) by evaluating tumour control, which will also be discussed in this chapter.

FDG PET/CT in colorectal cancer

Colorectal cancer is the third most frequent cancer worldwide. Although its incidence is increasing, mainly in those aged under50, mortality has decreased by 50% in the more developed countries, principally due to the adoption of new practices in prevention, diagnosis and treatment. In particular, the various diagnostic imaging modalities allow improved therapeutic decision-making, evaluation of the response and early detection of recurrence. The aim of this paper is to review the available scientific evidence on the value of positron emission tomography with ¹⁸F-FDG (¹⁸F-FDG PET/CT) in the colorectal cancer, with special emphasis on the indications of the guidelines and recommendations of the main international scientific associations regarding this imaging technique.

Prognostic utility of serial 18F-FDG-PET/CT in patients with locally advanced rectal cancer who underwent tri-modality treatment

OBJECTIVE

This study explored the value of serial 18-fludeoxyglucose-positron emission tomography (¹⁸F-FDG-PET/CT) in predicting disease-free survival (DFS) in locally advanced rectal cancer (LARC) treated with neoadjuvant chemoradiation (NCRT) and surgery.

METHODS

We prospectively studied 46 patients with LARC who underwent NCRT and surgery. ¹⁸F-FDG-PET/CT scans were performed at three time-points before surgery (pre-NCRT-PET1, during NCRT-PET2 and following completion of NCRT-PET3). The following semi-quantitative PET parameters were analysed at each time point: maximum standardized uptake value (SUVmax), SUVmean, metabolic tumour volume (MTV) and tumour lesion glycolysis (TLG). Absolute and percentage changes in these parameters were analysed between time points. Statistical analysis consisted of median tests, Cox regression and Kaplan-Meier analysis for DFS.

RESULTS

The median follow-up time was 24 months. A reduction in PET parameters showed statistically significant differences for patients with recurrence compared to those without; percentage changes in MTV between PET1 and PET3 (cut-off: 87%, p = 0.023), percentage changes in TLG between PET1 and PET3 (cut-off: 94%, p = 0.02) and absolute change in MTV PET1 and PET2 (cut-off: 10.25, p = 0.001).An absolute reduction in MTV between PET1 and PET3 (p=0.013), a percentage reduction in TLG between PET1 and PET2 (p=0.021), SUVmax and SUVmean at PET2 (p = 0.01, p = 0.027 respectively)were also prognostic indicators of recurrence.MTV percentage change between PET1 and PET2 and SUVmean percentage change between PET1 and PET3 were also trending towards significance (p = 0.052, p = 0.053 respectively).

CONCLUSION

Serial ¹⁸F-FDG-PET/CT is a potentially reliable non-invasive method to predict recurrence in patients with LARC. Volumetric parameters were the best predictors. This could allow risk-stratification in patients who may benefit from conservative management.

ADVANCES IN KNOWLEDGE

This paper will add to the literature in risk-stratifying patients with LARC based on prognosis, using ¹⁸F-FDG-PET/CT. This may improve patient outcomes by selecting suitable candidates for conservative management.

Validated imaging biomarkers as decision-making tools in clinical trials and routine practice: current status and recommendations from the EIBALL* subcommittee of the European Society of Radiology (ESR)

Observer-driven pattern recognition is the standard for interpretation of medical images. To achieve global parity in interpretation, semi-quantitative scoring systems have been developed based on observer assessments; these are widely used in scoring coronary artery disease, the arthritides and neurological conditions and for indicating the likelihood of malignancy. However, in an era of machine learning and artificial intelligence, it is increasingly desirable that we extract quantitative biomarkers from medical images that inform on disease detection, characterisation, monitoring and assessment of response to treatment. Quantitation has the potential to provide objective decision-support tools in the management pathway of patients. Despite this, the quantitative potential of imaging remains under-exploited because of variability of the measurement, lack of harmonised systems for data acquisition and analysis, and crucially, a paucity of evidence on how such quantitation potentially affects clinical decision-making and patient outcome. This article reviews the current evidence for the use of semi-quantitative and quantitative biomarkers in clinical settings at various stages of the disease pathway including diagnosis, staging and prognosis, as well as predicting and detecting treatment response. It critically appraises current practice and sets out recommendations for using imaging objectively to drive patient management decisions.

[Importance of FDG-PET/computed tomography in colorectal cancer]

BACKGROUND

Hybrid imaging FDG PET/CT (¹⁸F‑fluordeoxyglucose positron emission tomography/computed tomography) has gained increasing importance in oncology in recent years.

DIAGNOSIS

A focal increase in FDG uptake in the gastrointestinal tract may be due to colorectal carcinoma. Such a finding requires further clarification.

PRIMARY STAGING

Staging of the primary and locoregional lymph nodes remains a domain of established imaging modalities as FDG PET/CT does not provide a clear additional benefit. Liver metastases can be detected with high sensitivity by FDG PET/CT, but MRI is superior in small lesions.

RADIATION THERAPY PLANNING

So far FDG PET/CT plays a subordinate role in the radiation therapy planning of rectal cancer. However, it can potentially contribute to the optimization of planning target volumes.

THERAPY MONITORING

FDG PET/CT is suitable for monitoring therapy because morphological and metabolic changes of the tumor can be detected in early stages. This enables early detection of nonresponders after beginning neoadjuvant chemoradiation therapy of rectal cancer. FDG PET/CT can also be used for therapy control of liver metastases, especially after local therapeutic procedures.

DETECTION OF RECURRENCE

With clinical suspicion of local recurrence and increased tumor markers, FDG PET/CT is a valuable tool as tumor recurrence can be detected with high sensitivity and specificity.

Impact of PET/CT for Restaging Patients With Locally Advanced Rectal Cancer After Neoadjuvant Chemoradiation

BACKGROUND

A major challenge in identifying candidates for nonoperative management of locally advanced rectal cancer is predicting pathologic complete response (pCR) following chemoradiation. We evaluated pre- and post-CRT PET-CT imaging to predict pCR and prognosis in this set of patients undergoing resection after neoadjuvant therapy.

METHODS

We retrospectively identified patients from 2002 to 2015 with locally advanced rectal cancer who underwent CRT, pre- and post-CRT PET-CT imaging, and resection. Univariate and multivariate analysis was performed and receiver operating characteristic (ROC) curves were generated to evaluate the association of PET-CT characteristics with pCR and survival. ROC curves were generated to define optimal cutoff points for predictive PET-CT characteristics.

RESULTS

125 patients were included. pCR rate was 28%, and follow-up was 48 mo. On multivariable analysis, patients who had a pCR had lower median post-CRT maximal standardized uptake value (SUV_max) (3.2 versus 5.2, P = 0.009) and higher median %SUV decrease (72 versus 58%, P = 0.009). ROC curves were generated for %SUV_max decrease (AUC = 0.70) and post-CRT SUV (AUC = 0.69). Post-CRT SUV_max <4.3 and %SUV_max decrease of >66% were equally predictive of pCR with a sensitivity of 65%, specificity of 72%, PPV of 44%, and NPV of 86%. Median 5-y overall and relapse-free survival were improved for patients with post-CRT SUV <4.3 (OS: 86 versus 66%, P = 0.01; RFS: 75 versus 52%, P = 0.01) or %SUV decrease of >66% (OS, 82 versus 66%, P = 0.05; RFS, 75 versus 54%, P = 0.01).

CONCLUSIONS

PET/CT may be useful in identifying patients who did not achieve pCR, as well as overall survival in patients undergoing CRT for rectal cancer. Patients with a post-CRT SUV of >4.3 should be considered for operative management, as an estimated 86% of these patients will not have a pCR.