Biological Target Volume Overlapping Segmentation System Method for Avoiding False-Positive PET Findings in Assessing Response to Neoadjuvant Chemoradiation Therapy 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.

SUVmax and metabolic tumor volume: surrogate image biomarkers of KRAS mutation status in colorectal cancer

Purpose

The objective of this study was to explore the association between KRAS mutation status and PET/CT metabolic parameters in colorectal cancer (CRC) patients.

Materials and methods

One hundred and sixty-four CRC patients were enrolled in this study and received PET/CT examination before operation, then KRAS mutation status was analyzed through pathologically confirmed CRC samples. The association between tumor clinical characteristics and PET/CT metabolic parameters, including maximum standardized uptake value (SUVmax), SUVmean, and metabolic tumor volume (MTV), and KRAS mutation status was analyzed using chi-squared tests, Mann-Whitney U tests, and logistic regression analysis.

Results

The KRAS mutation type patients exhibited high MTV and high SUVmax using a threshold of 17.8 cm³ and 8.7 respectively and the predictive accuracy was 0.772 and 0.603 respectively. High MTV (P=0.001; 95% CI: 1.119-1.296) and high SUVmax (P=0.048; 95% CI: 0.564-0.985) were independent predictors for KRAS mutation status.

Conclusion

MTV and SUVmax were associated with KRAS mutation type in CRC patients. PET/CT metabolic parameters can be used for supplementing KRAS mutation status prediction in CRC patients.

Junior E, Machado AM, Mamede M. Individualized threshold for tumor segmentation in 18F-FDG PET/CT imaging: The key for response evaluation of neoadjuvant chemoradiation therapy in patients with rectal cancer?

Summary Introduction: The standard treatment for locally advanced rectal cancer (RC) consists of neoadjuvant chemoradiation followed by radical surgery. Regardless the extensive use of SUVmax in 18F-FDG PET tumor uptake as representation of tumor glycolytic consumption, there is a trend to apply metabolic volume instead. Thus, the aim of the present study was to evaluate a noninvasive method for tumor segmentation using the 18F-FDG PET imaging in order to predict response to neoadjuvant chemoradiation therapy in patients with rectal cancer. Method: The sample consisted of stage II and III rectal cancer patients undergoing 18F-FDG PET/CT examination before and eight weeks after neoadjuvant therapy. An individualized tumor segmentation methodology was applied to generate tumor volumes (SUV2SD) and compare with standard SUVmax and fixed threshold (SUV40%, SUV50% and SUV60%) pre- and post-therapy. Therapeutic response was assessed in the resected specimens using Dworak's protocol recommendations. Several variables were generated and compared with the histopathological results. Results: Seventeen (17) patients were included and analyzed. Significant differences were observed between responders (Dworak 3 and 4) and non-responders for SUVmax-2 (p<0.01), SUV2SD-2 (p<0.05), SUV40%-2 (p<0.05), SUV50%-2 (p<0.05) and SUV60%-2 (p<0.05). ROC analyses showed significant areas under the curve (p<0.01) for the proposed methodology with sensitivity and specificity varying from 60% to 83% and 73% to 82%, respectively. Conclusion: The present study confirmed the predictive power of the variables using a noninvasive individualized methodology for tumor segmentation based on 18F-FDG PET/CT imaging for response evaluation in patients with rectal cancer after neoadjuvant chemoradiation therapy.

Prediction of tumor response after neoadjuvant chemoradiotherapy in rectal cancer using (18)fluorine-2-deoxy-D-glucose positron emission tomography-computed tomography and serum carcinoembryonic antigen: a prospective study

PURPOSE

To investigate the association between (18)fluorine-2-deoxy-D-glucose positron emission tomography-computed tomography ((18)F-FDG PET/CT) parameters, serum carcinoembryonic antigen (CEA), and tumor response in patients with rectal cancer receiving neoadjuvant chemoradiotherapy (nCRT).

METHODS

Sixty-four patients with T3-4 and/or node-positive rectal cancer receiving nCRT followed by surgery were prospectively studied. PET/CT was performed before, and in 28 patients, both before and after nCRT. The pre-/post-nCRT maximum standardized uptake (SUVmax) values, differences between pre-/post-nCRT SUVmax (∆SUVmax), response index of SUVmax (RI-SUVmax), mean standardized uptake value (SUVmean), metabolic tumor volume (MTV), total lesion glycolysis (TLG), and CEA were measured. The ability of PET/CT parameters and CEA to predict Mandard's tumor regression grade (TRG) and pathological complete remission (pCR) were evaluated.

RESULTS

31 patients were identified as responders (TRG 1-2), and 19 exhibited pCR. For responders, significant differences were found for ΔSUVmax (24.88 vs. 15.39 g/ml, p = 0.037), RI-SUVmax (0.76 vs. 0.63, p = 0.025), ΔSUVmean (14.43 vs. 8.65 g/ml, p = 0.029), RI-SUVmean (0.77 vs. 0.63, p = 0.011), CEA-pre (6.30 vs. 27.86 μg/L, p < 0.001), CEA-post (2.22 vs. 5.49 μg/L, p = 0.002), ΔCEA (4.08 vs. 23.13 μg/L, p < 0.001), and RI-CEA (0.25 vs. 0.55, p = 0.002). Differences between pCR and non-pCR patients were noted as RI-SUVmean (0.77 vs. 0.65, p = 0.043), MTV-pre (9.87 vs. 14.62 cm(3), p = 0.045), CEA-pre (5.62 vs. 22.27 μg/L, p = 0.002), CEA-post (1.95 vs. 4.72 μg/L, p = 0.001), and ΔCEA (3.68 vs. 17.99 μg/L, p = 0.013). Receiver operating characteristic analysis revealed that RI-SUVmean exhibited the greatest accuracy in predicting responders, whereas CEA-post and ΔCEA exhibited the greatest accuracy in predicting pCR.

CONCLUSIONS

(18)F-FDG PET/CT parameters and CEA are accurate tools for predicting tumor response to nCRT in rectal cancer.

Correlation between PET/CT parameters and KRAS expression in colorectal cancer

PURPOSE

The objective of this study was to correlate the association between mutated KRAS and wild-type colorectal cancer (CRC) by using various F-FDG PET-related parameters.

METHODS

One hundred twenty-one CRC patients who had undergone preoperative PET/CT were included in this study. Several PET/CT-related parameters, including SUVmax and various thresholds of metabolic tumor volume, total lesion glycolysis, and PET/CT-based tumor width, were measured. Tumor- and PET/CT-related parameters were correlated with genomic expression between KRAS mutant and wild-type groups, using a Mann-Whitney U test and logistic regression analysis.

RESULTS

Colorectal cancer tumors with a mutated KRAS exhibited higher SUVmax and an increased accumulation of FDG among several threshold methods. Multivariate analysis showed that SUVmax and using a 40% threshold level for maximal uptake of TW (TW40%) were the 2 predictors of KRAS mutations. The odds ratio was 1.23 for SUVmax (P = 0.02; 95% confidence interval, 1.01-1.52) and 1.15 for TW40% (P = 0.02; 95% confidence interval, 1.02-1.30). The accuracy of SUVmax for predicting mutated KRAS was higher in patients with colon or sigmoid colon cancers, whereas it was TW40% in those with rectal cancers.

CONCLUSIONS

SUVmax and TW40% were associated in CRC with KRAS mutations. PET/CT parameters can supplement genomic analysis to determine KRAS expression in CRC.

Prediction of survival and cancer recurrence using metabolic volumetric parameters measured by 18F-FDG PET/CT in patients with surgically resected rectal cancer

OBJECTIVE

The goal of the present study was to determine whether the volumetric parameters such as metabolic tumor volume (MTV) and total lesion glycolysis (TLG) measured by F-FDG PET/CT could be used as prognostic factors for the recurrence-free survival (RFS) and overall survival (OS) in patients with surgically resected rectal cancer.

PATIENTS AND METHODS

A retrospective review identified 73 patients with surgically resected rectal cancer who received F-FDG PET/CT. Survival analysis was conducted using Kaplan-Meier analysis, and survival curves stratified by age, sex, lymph node status, surgical resection margin, American Joint Committee on Cancer (AJCC) stage, and volumetric parameters of F-FDG PET/CT were generated for the estimation of OS and RFS. Independent predictive factors for survival were determined using Cox proportional hazards model.

RESULTS

High MTV, high TLG, advanced AJCC stage, lymph node (+), and surgical margin (+) group showed shorter OS in rectal cancer patients. Cox proportional hazards regression analysis showed that only surgical margin (+) was associated with poor OS. The early AJCC stage, lower MTV, and lower TLG were associated with better RFS in the current study. Cox proportional hazards regression analysis reveals that the surgical margin (+) was the potent predictor of OS. However, none of the factors was associated with RFS.

CONCLUSIONS

In conclusion, the results of this study suggest that volumetric parameters of F-FDG PET/CT could be significant prognostic factors in surgically resected rectal cancer.