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ObjectivesIn the current clinical practice of thermal ablation treatment for liver tumors, achieving consistent and effective clinical outcomes across tumors of varying shapes, sizes and locations remains challenging. The aim of this study was to evaluate the repeatability of a novel robotic approach for configurable ablation of distinct tumor shapes and compare it to the standard ablation technique for creating ellipsoidal ablation volumes.Materials and methodsThe repeatability was evaluated in terms of width variability in created ablation volumes. Using a robotic navigation platform, custom ablation profiles configured with power, time, and distance parameters were designed to create four distinct ablation shapes. The profiles were applied for microwave ablation in a tissue-mimicking liver model. For comparison of ablation shape variability, six standard ellipsoidal shapes were created using the standard ablation technique by configuring power and time parameters. For each sample, the resulting ablation area was segmented, and the resulting shape width and length were calculated at the measurement points. Width variability was calculated as the median of the absolute pairwise differences in width at each measurement point, and configurable versus standard ablation shapes were compared using the Mann–Whitney U test.ResultsAll tissue-mimicking samples were successfully ablated using both configurable (n = 48) and standard ablation technique (n = 35). Study findings revealed noninferiority regarding repeatability of created ablation shapes using the robotic platform for configurable ablation, compared to created standard ellipsoidal ablation shapes (p < 0.001, 95% CI ≤ -0.05 mm, Δ = -0.22 mm). Median repeatability of created configurable shapes was 1.00 mm, and for standard shapes 1.22 mm. Maximal repeatability for both groups was below 3 mm.ConclusionThe repeatability of configurable ablation shapes was observed to be noninferior to the standard ablation shapes. Achieving configurable ablation volumes underscores the potential to advance personalization of thermal ablation treatment and broaden its applicability to distinct tumor cases. In-vivo validation is needed for evaluation of the clinical implications of this novel treatment technique.

BackgroundThree-dimensional (3D) volumetric ablation margin assessment after thermal ablation of liver tumors using software has been described, but its predictive value on treatment efficacy when accounting for other factors known to correlate ablation site recurrence (ASR) remains unknown.PurposeTo investigate 3D quantitative ablation margins (3D-QAMs) as an algorithm to predict ASR within 1 year after stereotactic microwave ablation (SMWA) for colorectal liver metastases (CRLM).Materials and MethodsSixty-five tumors in 47 patients from a prospective multicenter study of patients undergoing SMWA for CRLM were included in this retrospective 3D-QAM analysis. Using a previously developed algorithm, 3D-QAM defined as the distribution of tumor to ablation surface distances was assessed in co-registered pre- and post-ablation CT scans. The discriminatory power and optimal cutoff values for 3D-QAM were assessed using receiver operating characteristic (ROC) curves. Multivariable logistic regression analysis using generalized estimating equations was applied to investigate the impact of various 3D-QAM outputs on 1-year ASR while accounting for other known influencing factors.ResultsTen of the 65 (15.4%) tumors included for 3D-QAM analysis developed ASR. ROC analyses identified i) 3D-QAM 23% of the tumor surface, ii) 3D-QAM 45%, and iii) the minimal ablation margin (MAM) as the 3D-QAM outputs with optimal discriminatory qualities. The multivariable regression model without 3D-QAM yielded tumor diameter and KRAS mutation as 1-year ASR predictors. When adding 3D-QAM, this factor became the main predictor of 1-year ASR [odds ratio (OR) 21.67 (CI 2.48, 165.21) if defined as >23%

BackgroundStereotactic navigation techniques aim to enhance treatment precision and safety in minimally invasive thermal ablation of liver tumors. We qualitatively reviewed and quantitatively summarized the available literature on procedural and clinical outcomes after stereotactic navigated ablation of malignant liver tumors.MethodsA systematic literature search was performed on procedural and clinical outcomes when using stereotactic or robotic navigation for laparoscopic or percutaneous thermal ablation. The online databases Medline, Embase, and Cochrane Library were searched. Endpoints included targeting accuracy, procedural efficiency, and treatment efficacy outcomes. Meta-analysis including subgroup analyses was performed.ResultsThirty-four studies (two randomized controlled trials, three prospective cohort studies, 29 case series) were qualitatively analyzed, and 22 studies were included for meta-analysis. Weighted average lateral targeting error was 3.7 mm (CI 3.2, 4.2), with all four comparative studies showing enhanced targeting accuracy compared to free-hand targeting. Weighted average overall complications, major complications, and mortality were 11.4% (6.7, 16.1), 3.4% (2.1, 5.1), and 0.8% (0.5, 1.3). Pooled estimates of primary technique efficacy were 94% (89, 97) if assessed at 1–6 weeks and 90% (87, 93) if assessed at 6–12 weeks post ablation, with remaining between-study heterogeneity. Primary technique efficacy was significantly enhanced in stereotactic vs. free-hand targeting, with odds ratio (OR) of 1.9 (1.2, 3.2) (n = 6 studies).ConclusionsAdvances in stereotactic navigation technologies allow highly precise and safe tumor targeting, leading to enhanced primary treatment efficacy. The use of varying definitions and terminology of safety and efficacy limits comparability among studies, highlighting the crucial need for further standardization of follow-up definitions.

BackgroundIn thermal ablation of liver tumors, complete coverage of the tumor volume by the ablation volume with a sufficient ablation margin is the most important factor for treatment success. Evaluation of ablation completeness is commonly performed by visual inspection in 2D and is prone to inter-reader variability. This work aimed to introduce a standardized approach for evaluation of ablation completeness after CT-guided thermal ablation of liver tumors, using volumetric quantitative ablation margins (QAM).MethodsA QAM computation metric based on volumetric segmentations of tumor and ablation areas and signed Euclidean surface distance maps was developed, including a novel algorithm to address QAM computation in subcapsular tumors. The code for QAM computation was verified in artificial examples of tumor and ablation spheres simulating varying scenarios of ablation margins. The applicability of the QAM metric was investigated in representative cases extracted from a prospective database of colorectal liver metastases (CRLM) treated with stereotactic microwave ablation (SMWA).ResultsApplicability of the proposed QAM metric was confirmed in artificial and clinical example cases. Numerical and visual options of data presentation displaying substrata of QAM distributions were proposed. For subcapsular tumors, the underestimation of tumor coverage by the ablation volume when applying an unadjusted QAM method was confirmed, supporting the benefits of using the proposed algorithm for QAM computation in these cases. The computational code for developed QAM was made publicly available, encouraging the use of a standard and objective metric in reporting ablation completeness and margins.ConclusionThe proposed volumetric approach for QAM computation including a novel algorithm to address subcapsular liver tumors enables precision and reproducibility in the assessment of ablation margins. The quantitative feedback on ablation completeness opens possibilities for intra-operative decision making and for refined analyses on predictability and consistency of local tumor control after thermal ablation of liver tumors.

Background: Therapeutic success of thermal ablation for liver tumors depends on precise placement of ablation probes and complete tumor destruction with a safety margin. We investigated factors influencing targeting accuracy and treatment efficacy of percutaneous stereotactic image-guided microwave ablation (SMWA) for malignant liver neoplasms.Materials and methods: All consecutive patients treated with SMWA for malignant liver tumors over a 3-year period were analyzed. A computed tomography-based navigation system was used for ablation probe trajectory planning, stereotactic probe positioning, and validation of probe positions and ablation zones. Factors potentially influencing targeting accuracy [target positioning error (TPE)] and treatment efficacy within 6 months [ablation site recurrence (ASR)] were analyzed in a multivariable regression model, including challenging lesion locations (liver segments I, VII, and VIII; subphrenic location).Results: Three hundred one lesions (174 hepatocellular carcinomas, 87 colorectal liver metastases, 17 neuroendocrine tumors, and 23 others) were targeted in 191 interventions in 153 patients. The median TPE per ablation probe was 2.9 ± 2.3 mm (n = 384). Correction of ablation probe positions by repositioning was necessary in 4 out of 301 lesions (1%). Factors significantly influencing targeting accuracy were cirrhosis (R 0.67, CI 0.22–1.12) and targeting trajectory length (R 0.21, CI 0.12–0.29). Factors significantly influencing early ASR were lesion size >30 mm (OR 5.22, CI 2.44–11.19) and TPE >5 mm (OR 2.48, CI 1.06–5.78). Challenging lesion locations had no significant influence on targeting accuracy or early ASR.Conclusions: SMWA allows precise and effective treatment of malignant liver tumors even for lesions in challenging locations, with treatment efficacy depending on targeting accuracy in our model. Allowing for many tumors to be safely reached, SMWA has the potential to broaden treatment eligibility for patients with otherwise difficult to target tumors.