Minimal Ablative Margin Associated With Local Tumor Progression

Minimal ablative margin (MAM) was found to be independently associated with local tumor progression (LTP) after thermal ablation in patients with colorectal liver metastases (CRLM), according to a study published in European Radiology.¹

CRLM can be treated using percutaneous thermal ablation, with radiofrequency and microwave ablation the most common types. Thermal ablation is usually used in patients who cannot have surgery.² However, it has been associated with higher rates of LTP, with MAM the best predictor of LTP. Image fusion with 3-dimensional volumetric has been used for the MAM. This study aimed to evaluate the association between LTP following thermal ablation of CRLM guided by computer tomography (CT).

There were 3 academic institutions that provided data for this retrospective study. Patients were included if they were treated for local lesions that were treatment-naïve, had intraprocedural pre- and post-ablation contrast-enhanced CT imaging available, and more than 12 months of imaging follow-up. All patients were treated between January 2009 and May 2021 across the 3 different centers.

Minimal ablative margin associated with local tumor progression in colorectal liver metastases | Image credit: Cinefootage Visuals - stock.adobe.com

All patients had routine imaging every 3 months for the first year and then imaging was done every 3 to 6 months afterward. Tumor focus within or at the border of the ablation zone during the follow-up after a documented complete ablation was defined as an LTP. All imaging data were reviewed at 2 of the institutions included.

There were 103 patients with 173 CRLM included in the study who had a mean (SD) age of 67 (10) years and a mean diameter of the tumor at 1.9 (1.1) cm. There was a median (IQR) follow-up of 31 (22-47) months and the incidence of LTP was 12.1%. Technical success was found in all tumors.

MAM of 5 mm or more, between 0 and 5 mm, and 0 mm or less were measured in 46.2%, 46.2%, and 7.6% when using automatic non-rigid (Ablation-fit) software. These measurements were 45.7%, 45.7% and 8.6% when using semi-automatic rigid co-registration (SAFIR) software. LTP was found in 0%, 16.3%, and 61.5% of tumors measured by aflation-fit compared with 0%, 7.6%, and 100% when measured with SAFIR. The smallest MAM where there was no LTP observed was 4 mm or smaller for Ablation-fit and 5 mm or small for SAFIR.

Age (HR, 0.95; 95% CI, 0.92-0.99), tumor size (HR, 1.04; 95% CI, 1.00-1.07), and MAM of each software (Ablation-fit: HR, 0.51; 95% CI, 0.41-0.64 vs SAFIR: HR, 0.49; 95% CI, 0.41-0.59) were all associated with LTP. There was excellent diagnostic performance for discriminating between cases of LTP and without LTP for both Ablation-fit (area under curve, 0.90; 95% CI, 0.86-0.95) and SAFIR (area under curve, 0.96; 95% CI, 0.91-1.00).

There were some limitations to this study. This was a retrospective study that was non-consecutive for all centers, which could have introduced bias. MAM was not calculated for tumors less than 0 mm and more than 10 mm due to differences in ablation confirmation software. Intermediate re-ablation within the same session was not evaluated. Reader variability affects the results of the study as well.

The researchers concluded that MAM was associated with LTP after thermal ablation of CRLM when using 2 confirmation software. Local control was found in ablations that had MAM of 5 mm or higher. Future cut-off points can be determined using confirmation software to determine the best cut-off point.

References

1. Laimer G, Verdonschot KHM, Kopf L, et al. Multicenter and inter-software evaluation of ablative margins after thermal ablation of colorectal liver metastases. Eur Radiolog. Published online August 2, 2024. doi:10.1007/s00330-024-10956-5
2. Liver metastasis, cancer spread to the liver. Froedtert & Medical College of Wisconsin. 2024. Accessed August 5, 2024. https://www.froedtert.com/colorectal-cancer/metastic-disease/liver-metastasis