Comparison of FDG-PET, PET/CT and MRI for follow-up of colorectal liver metastases treated with radiofrequency ablation: Initial results

doi:10.1016/j.ejrad.2007.11.017

European Journal of Radiology

Volume 67, Issue 2, August 2008, Pages 362-371

https://doi.org/10.1016/j.ejrad.2007.11.017 Get rights and content

Abstract

Purpose

Morphologic imaging after radiofrequency ablation (RFA) of liver metastases is hampered by rim-like enhancement in the ablation margin, making the identification of local tumor progression (LTP) difficult. Follow-up with PET/CT is compared to follow-up with PET alone and MRI after RFA.

Methods and materials

Sixteen patients showed 25 FDG-positive colorectal liver metastases in pre-interventional PET/CT. Post-interventional PET/CT was performed 24 h after ablation and was repeated after 1, 3 and 6 months and then every 6 months. PET and PET/CT data were compared with MR data sets acquired within 14 days before or after these time points. Either histological proof by biopsy or resection, or a combination of contrast-enhanced CT at fixed time points and clinical data served as a reference.

Results

The 25 metastases showed a mean size of 20 mm and were treated with 39 RFA sessions. Ten lesions which developed LTP received a second round of RFA; four lesions received three rounds of treatment. The mean follow-up time was 22 months. Seventy-two PET/CT and 57 MR examinations were performed for follow-up. The accuracy and sensitivity for tumor detection was 86% and 76% for PET alone, 91% and 83% for PET/CT and 92% and 75% for MRI, respectively.

Conclusions

In comparison to PET alone, PET/CT was significantly better for detecting LTP after RFA. There were no significant differences between MRI and PET/CT. These preliminary results, however, need further verification.

Introduction

Colorectal cancer is the most common malignancy leading to liver metastases and one of the most common malignant diseases in the western hemisphere. In Europe, colorectal carcinoma incidence has surpassed that of bronchial carcinoma. Moreover, it currently has the highest incidence of all malignancies in Europe [1]. For colorectal cancer, metastatic spread of the disease to the liver and progression of the liver metastases, not local recurrence, are the most important limiting factors for survival. Surgical resection of liver metastases remains the method of choice for curative treatment, but only a minority (10–25%) of patients are candidates for resection therapy [2]. Exclusion criteria for surgery include lesion localization that is not suited to surgical intervention, the presence of more than five nodules, impaired liver function and relevant co-morbidities.

Within the last two decades, a variety of local ablative therapies, e.g., interstitial laser therapy, microwave ablation, and radiofrequency ablation (RFA), have been introduced and evaluated. Of these, RFA has been the most intensely studied therapy. The value of RFA as an adjunct or replacement method for surgical resection depends on its efficacy, measured as the rate of local tumor progression (LTP) after treatment. This makes a thorough follow-up after ablation with repeated imaging essential for tumor control. Follow-up is based on imaging, which is the most reliable tool for detection of new intrahepatic tumors. Contrast-enhanced multi-detector-computer tomography (CE-CT) is the mainstay of staging and follow-up [3], but magnetic resonance imaging (MRI), especially when performed with liver-specific contrast agents, has been shown to be superior to CT in the detection of liver metastases [4]. Contrast-enhanced percutaneous ultrasound (CEUS) has demonstrated diagnostic performance and confidence similar to those of contrast-enhanced CT [5].

Positron emission tomography (PET) with 18-Fluorodeoxyglucose (¹⁸FDG) is a very sensitive and accurate tool for the diagnosis of tumor manifestations in patients with colorectal carcinoma [6]. PET/CT has the potential to overcome the limitations of PET (like low spatial resolution) by adding the morphologic information of CT and is superior to CE-CT for the detection of recurrent intrahepatic tumors after hepatectomy and of extrahepatic metastases [7]. Until now, there has been no data regarding the diagnostic accuracy of FDG-PET/CT after local ablative treatment of malignant liver lesions.

Therefore, the aim of this study was to evaluate the diagnostic value of FDG-PET alone, the combined imaging modality PET/CT and contrast-enhanced MRI to detect LTP after CT-guided RFA of colorectal liver metastases.

Section snippets

Patients

The protocol for this study was approved by the human studies and ethics committee of our institution. Detailed written informed consent for all imaging procedures as well as the planned intervention was obtained from each enrolled patient.

Since January 2002, all patients referred to our institution for tumor ablation of colorectal liver metastases were prospectively examined with PET/CT prior to the planned intervention. Selection of RFA treatment was based on an interdisciplinary consensus

Radiofrequency ablation

The 16 enrolled patients showed 25 liver metastases (1–5 per patient, mean 1.8) with a mean size of 20 mm over the largest diameter (10–43 mm). Nine of the 25 lesions were located within 10 mm of an intrahepatic vessel with a diameter larger than 5 mm. The mean size of the ablation zone was 38 mm (29–56 mm) over the largest diameter.

Clinical course

The mean time of follow-up was 22 months (678 ± 350 days, range 361–1369 days).

Discussion

One of the advantages of RFA as well as other thermal ablative therapies for the treatment of colorectal liver metastases is that it may offer surgically inoperable patients a therapy option which can spare the parenchyma and allows for percutaneous access to a given tumor in situ. On the other hand, all locally destructive procedures have the following Achilles heel: a constant follow-up is mandatory to detect local tumor progression of the treated malignant lesion. Therefore, the future of

Conclusion

¹⁸FDG-PET/CT was a significantly better method for evaluation of the therapy response of colorectal metastases after RFA compared to PET alone. This is due to the additional morphologic information given by the CT component. There were no significant differences between the MRI and ¹⁸FDG-PET/CT imaging modalities. A general problem in the follow-up of liver metastases treated with RFA is the detection of small viable tumor clusters in the ablation necrosis zone. These can be missed by all three

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Comparison of FDG-PET, PET/CT and MRI for follow-up of colorectal liver metastases treated with radiofrequency ablation: Initial results

Abstract

Purpose

Methods and materials

Results

Conclusions

Introduction

Section snippets

Patients

Radiofrequency ablation

Clinical course

Discussion

Conclusion

Cancer incidence and mortality in Europe, 2004

Ann Oncol

Resection of colorectal liver metastases

World J Surg

Liver metastases of colorectal cancer: US, CT or MR?

Cancer Imaging

Colorectal liver metastases: CT, MR imaging, and PET for diagnosis—meta-analysis

Radiology

Comparison of contrast-enhanced ultrasonography versus baseline ultrasound and contrast-enhanced computed tomography in metastatic disease of the liver: diagnostic performance and confidence

Eur Radiol

FDG-PET for the pre-operative evaluation of colorectal liver metastases

Eur J Surg Oncol

Does the novel PET/CT imaging modality impact on the treatment of patients with metastatic colorectal cancer of the liver?

Ann Surg

Dual-modality PET/CT imaging: the effect of respiratory motion on combined image quality in clinical oncology

Eur J Nucl Med Mol Imaging

Image-guided tumor ablation: standardization of terminology and reporting criteria