Identification of A0 minimum ablative margins for colorectal liver metastases: multicentre, retrospective study using deformable CT registration and artificial intelligence-based autosegmentation

Abstract

Background: Several ablation confirmation software methods for minimum ablative margin assessment have recently been developed to improve local outcomes for patients undergoing thermal ablation of colorectal liver metastases. Previous assessments were limited to single institutions mostly at the place of development. The aim of this study was to validate the previously identified 5 mm minimum ablative margin (A0) using autosegmentation and biomechanical deformable image registration in a multi-institutional setting.

Methods: This was a multicentre, retrospective study including patients with colorectal liver metastases undergoing CT- or ultrasound-guided microwave or radiofrequency ablation during 2009-2022, reporting 3-year local disease progression (residual unablated tumour or local tumour progression) rates by minimum ablative margin across all institutions and identifying an intraprocedural contrast-enhanced CT-based minimum ablative margin associated with a 3-year local disease progression rate of less than 1%.

Results: A total of 400 ablated colorectal liver metastases (median diameter of 1.5 cm) in 243 patients (145 men; median age of 62 [interquartile range 54-70] years) were evaluated, with a median follow-up of 26 (interquartile range 17-40) months. A total of 119 (48.9%) patients with 186 (46.5%) colorectal liver metastases were from international institutions B, C, and D that were not involved in the software development. Three-year local disease progression rates for 0 mm, >0 and <5 mm, and 5 mm or larger minimum ablative margins were 79%, 15%, and 0% respectively for institution A (where the software was developed) and 34%, 19%, and 2% respectively for institutions B, C, and D combined. Local disease progression risk decreased to less than 1% with an intraprocedurally confirmed minimum ablative margin greater than 4.6 mm.

Conclusion: A minimum ablative margin of 5 mm or larger demonstrates optimal local oncological outcomes. It is proposed that an intraprocedural minimum ablative margin of 5 mm or larger, confirmed using biomechanical deformable image registration, serves as the A0 for colorectal liver metastasis thermal ablation.

Fig. 1

Study flow chart summarized across all institutions *Residual tumour was detected at the end of the procedure, but re-ablation was deferred to a later ablation session. LRT, locoregional therapy, LTP, local tumour progression, CRLMs, colorectal liver metastases.

Fig. 2

Intrahepatic new tumor incidence and overall survival Kaplan-Meier curves a Cumulative incidence of development of new colorectal liver metastases after the initial ablation procedure for colorectal liver metastases. b Overall survival after the initial ablation procedure for colorectal liver metastases. CRLMs, colorectal liver metastases.

Fig. 3

Cumulative incidence of local disease progression by minimum ablative margins a Cumulative incidence of local disease progression according to minimum ablative margins for institution A. b Cumulative incidence of local disease progression according to minimum ablative margins for institutions B, C, and D. MAM, minimum ablative margin; LDP, local disease progression.

Fig. 4

Receiver operating characteristic (ROC) curves for predicting 3-year local disease progression by minimum ablative margins measured using intraprocedural versus periprocedural contrast-enhanced CT imaging CECT, contrast-enhanced CT; AUROC, area under the receiver operating curve.

Fig. 5

Risk of local disease progression according to minimum ablative margins with thresholds for sufficient minimum ablative margins (less than 5% local disease progression risk) a Measured using intraprocedural imaging. b Measured using periprocedural imaging. MAM, minimum ablative margin; DR, point of diminishing returns (the minimum ablative margin threshold where additional 1-mm increases in the minimum ablative margin yielded a less than 1% decrease in risk for local disease progression); LDP, local disease progression.