18F-FDG PET as novel imaging biomarker for disease progression after ablation therapy in colorectal liver metastases

A Review of Imaging Methods to Assess Ultrasound-Mediated Ablation

Ultrasound ablation techniques are minimally invasive alternatives to surgical resection and have rapidly increased in use. The response of tissue to HIFU ablation differs based on the relative contributions of thermal and mechanical effects, which can be varied to achieve optimal ablation parameters for a given tissue type and location. In tumor ablation, similar to surgical resection, it is desirable to include a safety margin of ablated tissue around the entirety of the tumor. A factor in optimizing ablative techniques is minimizing the recurrence rate, which can be due to incomplete ablation of the target tissue. Further, combining focal ablation with immunotherapy is likely to be key for effective treatment of metastatic cancer, and therefore characterizing the impact of ablation on the tumor microenvironment will be important. Thus, visualization and quantification of the extent of ablation is an integral component of ablative procedures. The aim of this review article is to describe the radiological findings after ultrasound ablation across multiple imaging modalities. This review presents readers with a general overview of the current and emerging imaging methods to assess the efficacy of ultrasound ablative treatments.

The Role of 18F-FDG PET/CT in Evaluating the Efficacy of Radiofrequency Ablation in Metastatic and Primary Liver Tumors: Preliminary Results

Objectives:

The aim of the study was to investigate the role of ¹⁸fluorine-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography/computed tomography (PET/CT) for evaluating the efficacy of radiofrequency ablation (RFA) in primary and metastatic liver tumors compared with contrast-enhanced ultrasound examination (CEUS) and to find its place in overall staging and the follow-up diagnostic algorithm.

Methods:

PET/CT examinations were performed 2 months after RFA for 20 patients with a total of 34 liver lesions. CEUS was performed within 10 days after PET/CT, and the results were compared. Seven patients were staged with PET/CT and the others with a contrast-enhanced CT.

Results:

A total of 48 ¹⁸F-FDG PET/CT examinations were performed. We observed complete response in 8 patients (40%), 2 patients (10%) had stable disease, one (5%) had partial response, and 9 patients (45%) had progression (including 2 cases with extrahepatic involvement). Compared with CEUS, there was a mismatch in 3 cases. Five patients underwent additional RFA for 7 lesions.

Conclusion:

According to our preliminary data, PET/CT may be a valuable method, with comparable or eventually even better sensitivity than CEUS, for early evaluation of the efficacy of RFA for the treatment of metastatic and primary liver lesions and planning of future treatment. PET/CT might be recommended as a staging method before undergoing RFA of liver lesions for determining the local extent of the disease in the liver in combination with CEUS with an advantage in visualization of extrahepatic involvement. However, more patients need to be investigated in order to demonstrate and confirm the obtained results with certainty.

Current state of the art imaging approaches for colorectal liver metastasis

One of the most common cancers worldwide, colorectal cancer (CRC) has been associated with significant morbidity and mortality and therefore represents an enormous burden to the health care system. Recent advances in CRC treatments have provided patients with primary and metastatic CRC a better long-term prognosis. The presence of synchronous or metachronous metastasis has been associated, however, with worse survival. The most common site of metastatic disease is the liver. A variety of treatment modalities aimed at targeting colorectal liver metastases (CRLM) has been demonstrated to improve the prognosis of these patients. Loco-regional approaches such as surgical resection and tumor ablation (operative and percutaneous) can provide patients with a chance at long-term disease control and even cure in select populations. Patient selection is important in defining the most suitable treatment option for CRLM in order to provide the best possible survival benefit while avoiding unnecessary interventions and adverse events. Medical imaging plays a crucial role in evaluating the characteristics of CRLMs and disease resectability. Size of tumors, proximity to adjacent anatomical structures, and volume of the unaffected liver are among the most important imaging parameters to determine the suitability of patients for surgical management or other appropriate treatment approaches. We herein provide a comprehensive overview of current-state-of-the-art imaging in the management of CRLM, including staging, treatment planning, response and survival assessment, and post-treatment surveillance. Computed tomography (CT) scan and magnetic resonance imaging (MRI) are two most commonly used techniques, which can be used solely or in combination with functional imaging modalities such as positron emission tomography (PET) and diffusion weighted imaging (DWI). Providing up-to-date evidence on advantages and disadvantages of imaging modalities and tumor assessment criteria, the current review offers a practice guide to assist providers in choosing the most suitable imaging approach for patients with CRLM.