European Radiology: The detection value of CT in single-shot microwave ablation of liver tumors

Percutaneous thermal ablation therapy is one of the main treatment options for primary and metastatic liver tumors, such as hepatocellular carcinoma (HCC) and colorectal liver metastases (CRLM) are its main indications
.
Radiofrequency ablation (RFA) is the most widely studied technique, while microwave ablation (MWA) is widely used due to its ability to achieve larger ablation areas and shorter ablation times
.
In ablation therapy, local tumor control is the primary goal and can improve long-term patient outcomes
.
Currently, the widely accepted criteria for minimal ablation margins are HCC ≥ 5 mm and CRLM ≥ 10 mm, which can significantly reduce local tumor progression (LTP) rates
.

The technical success rate of ablation is routinely assessed by contrast-enhanced CT (CECT) or MRI after ablation, and repeated ablation is performed based on imaging findings
.
Utilizing intraoperative CECT with multiplanar reconstruction (MPR) allows the assessment of 3D ablation margin status by comparing the post-ablation image with the pre-treatment image, which not only helps determine the extent of the tumor to be ablated, but also pinpoints the potential need for additional Overlap ablated edges
.
To date, little is known about the added value of insurance CECT imaging during liver tumor ablation compared to traditional procedures that only include post-ablation imaging
.

Recently, a study published in European Radiology evaluated the value of minimal ablation margin control in MWA monitored by intraoperative CECT for successful ablation of liver tumors, providing the possibility to improve the treatment success rate and prognosis of such patients
.

This study retrospectively included 334 liver tumors (240 liver cancer [HCC] and 94 colorectal liver metastases [CRLMs]) in 172 patients treated with percutaneous MWA
.
The MAM of each tumor was assessed using intraoperative CECT after completion of the intended ablation, allowing additional ablation of any potentially insufficient margins within the course of the session
.
MRI was performed immediately after MWA to determine complete ablation coverage of the tumor and final MAM status
.
Cumulative local tumor progression (LTP) rates were estimated using the Kaplan-Meier method
.
To identify predictors of LTP, Cox regression analysis was performed using a shared frailty model
.
 

Intraoperative CECT findings prompted additional ablation in 18.
9% (63/334) of the tumors
.
Final complete ablation coverage was achieved in 99.
4% (332/334) and 77.
5% (259/334) of tumors as determined by MRI, with LTP rates of 3.
2%, 7.
5% and 7.
5% at 6 months, 1 year and 2 years, respectively.
12.
9%; and 1.
0%, 2.
1% and 6.
9%
.
MAM insufficiency on MRI after MWA, perivascular tumor location and tumor size (cm) were independent risk factors for LTP (hazard ratio=14.
4, 6.
0 and 1.
1, p<0.
001, p=0.
003 and p=0.
011), while capsular This was not the case for inferior location and histology (HCC vs CRLM)
.
 

Figure A patient with hepatocellular carcinoma (HCC) undergoing microwave ablation (MWA)
.
Axial CT arterial phase image before treatment (a) shows a hypervascular HCC in the eighth segment of the liver
.
Intraoperative CT image (b) shows insufficient ablation margins (stars) on the right side of the tumor after completion of the intended ablation
.
Additional ablation was performed immediately to cover under-margined sites by repositioning the MWA probe (c)
.
On MRI after MWA, anterior T1-weighted axial image (d) shows a margin of more than 5 mm (dashed line) around the tumor surface, even on the right side of the tumor
.
Note that in this case, artificial ascites was used to minimize thermal damage to the diaphragm due to the tumor's subcapsular location

The present study demonstrates that in MWA of liver tumors, obtaining sufficient minimal ablation margins is highly predictive for local tumor control
.
Intraoperative CECT monitoring of minimal ablation margins helps identify potential minimal tumor margins and guide immediate intraoperative additional ablation, thus optimizing local tumor control in a single treatment
.

Original source:

Ijin Joo, Kenneth W Morrow, Steven S Raman, et al.
CT-monitored minimal ablative margin control in single-session microwave ablation of liver tumors: an effective strategy for local tumor control.
DOI: 10.
1007/s00330-022-08723-5