European Radiology: Are all local progressions of liver cancer related to thermal ablation?

Hepatocellular carcinoma (HCC) has attracted much attention due to its high recurrence rate, and its treatment effect and prognosis are poor
.
As one of many treatments for HCC, thermal ablation has been recommended
by some guideline crops as an important radical treatment.
Due to its minimally invasive, reproducible and cost-effective nature, thermal ablation has been accepted
in clinical practice.
However, many studies have shown that recurrence-free survival after thermal ablation is lower than surgical resection, and that the incidence of local tumor progression (LTP) after ablation is higher (15-20%) than surgical treatment (5-10%)
.

LTP is a unique type of recurrence that occurs around
the ablation zone (AZ).
Previous studies have mostly shown that LTP is one of the important adverse consequences of
thermal ablation incompleteness.
However, the cause of LTP is unclear and can be broadly divided into ablative and non-ablative factors
.
The former includes insufficient ablation energy, incorrect position of the ablation needle, and heat dissipation effects on
surrounding tissues.
The latter include tumor microvascular invasion, small lesions that are not visible on radiographic, and tumor recurrence
near AZ.
Therefore, we believe that different causes of LTP should be distinguished to reveal the actual proportion of LTP in tumor recurrence after ablation and minimize the accurate assessment
of confounding factors for treatment effect.

Unlike surgery, thermal ablation releases energy that inactivates
the tumor and surrounding tissue in situ.
For thermal ablation, sufficient extension beyond the tumor boundary is a key factor in achieving complete tumor destruction, and the ablation edge (AM) represents this region
.
How to evaluate AM is a fundamental question
in treatment.
Among them, 3D visual image fusion is one of
the most prominent techniques due to its accuracy and quantification.

Recently, a study published in the journal European Radiology used 3D visualization and image fusion technology to effectively classify LTP caused by ablation and non-ablative factors, which provided a reference for
further improving the formulation of treatment plans for thermal ablation and improving the prognosis of patients.

This review included 185 cases of LTP that occurred within 1 cm of the ablation zone (AZ) after clinical radical thermal ablation of liver cancer ≤ 5 cm between 2010 and 2019
。 The AZ is divided into 8 quadrants by coronal, sagittal and water levels
.
Using two methods, visual assessment (VA) before and after MRI and tumor mapping (MF) visualized in 3D before and after MRI fusion, three physicians assess which AZ quadrant includes the shortest ablation edge (AM).

LTP subclassification is based on whether LTP is exposed to the AZ edge (contact LTP and discrete LTP) and its occurrence
at different time points (12, 18, and 24 months).

Fleiss Kappa for VA and MF is 0.
769 and 0.
886
, respectively.
Cohen's Kappa coefficient between VA and MF is 0.
830
.
For all LTPs, 98/185 (53.
0%) occurred in the shortest AM quadrant, showing a clear central propensity (P < 0.
001).

However, only 8/51 (15.
7%) separated LTP and 6/39 (15.
4%) LTP occurred in the shortest AM quadrant after 24 months, which showed no uniform difference (P = 0.
360 and 0.
303).

Image fusion and 3D visualization process, (A) MRI before ablation; (B) MRI after ablation; (C) Pre- and post-ablation MRI image fusion; (D) Spatial relationship
between pre-ablation tumor and post-ablation ablation zone in three-dimensional visualization.
The pink line is the outline
of the liver.
The green line is the outline
of the AZ.
The yellow line is the outline
of the tumor.
AZ = ablation zone

This study shows that MF is an objective and convenient means to
evaluate AM after thermal ablation of HCC.
This study found that the distribution of LTP is not uniform, but there is a trend
in the shortest AM quadrant.
Among them, contact LTP and LTP within 24 months meet this law and can be called ablation-related LTP
.
However, the distribution of isolated LTP and LTP after 24 months is uniform and can be referred to as non-ablation-related LTP
.

Original source:

Wen-Zhen Ding,Sisi Liu,Fangyi Liu,et al.
Are all local tumour progressions of HCC related to thermal ablation? A study of the causes and classification of local tumour progression.
DOI:10.
1007/s00330-022-08913-1