Sequential and Simultaneous 4-Antenna Microwave Ablation in an Ex Vivo Bovine Liver Model

Simulation of Image-Guided Microwave Ablation Therapy Using a Digital Twin Computational Model

Emerging computational tools such as healthcare digital twin modeling are enabling the creation of patient-specific surgical planning, including microwave ablation to treat primary and secondary liver cancers. Healthcare digital twins (DTs) are anatomically one-to-one biophysical models constructed from structural, functional, and biomarker-based imaging data to simulate patient-specific therapies and guide clinical decision-making. In microwave ablation (MWA), tissue-specific factors including tissue perfusion, hepatic steatosis, and fibrosis affect therapeutic extent, but current thermal dosing guidelines do not account for these parameters. This study establishes an MR imaging framework to construct three-dimensional biophysical digital twins to predict ablation delivery in livers with 5 levels of fat content in the presence of a tumor. Four microwave antenna placement strategies were considered, and simulated microwave ablations were then performed using 915 MHz and 2450 MHz antennae in Tumor Naïve DTs (control), and Tumor Informed DTs at five grades of steatosis. Across the range of fatty liver steatosis grades, fat content was found to significantly increase ablation volumes by approximately 29-l42% in the Tumor Naïve and 55-60% in the Tumor Informed DTs in 915 MHz and 2450 MHz antenna simulations. The presence of tumor did not significantly affect ablation volumes within the same steatosis grade in 915 MHz simulations, but did significantly increase ablation volumes within mild-, moderate-, and high-fat steatosis grades in 2450 MHz simulations. An analysis of signed distance to agreement for placement strategies suggests that accounting for patient-specific tumor tissue properties significantly impacts ablation forecasting for the preoperative evaluation of ablation zone coverage.

Microwave ablation using two simultaneous antennas for the treatment of liver malignant lesions: a 3 year single-Centre experience

BACKGROUND

sequential or simultaneous applications of multiple antennas have been proposed to create larger ablation zone; however, there is a lack of data in patients affected by liver tumors, with potentially different results from animal liver models. The purpose of this study was to evaluate efficacy and safety of liver percutaneous microwave ablation using simultaneous activation of two antennas to treat lesions bigger than 2,5 cm; particularly the focus was assessing whether the ratio of ablation zone volume in millimeters to applied energy in kilojoules [R(AZ:E)] differs between hepatocellular carcinoma in a cirrhotic liver and liver metastasis and if it is correlated to complications incidence or recurrence of disease.

METHODS

Fifty-five liver microwave ablation performed with two simultaneous antennas from March 2017 to June 2021 were retrospectively reviewed; 9 procedures were excluded due to the association with Chemoembolization. Size, shape, volume of lesions and ablation zones were recorded. Technical success was defined as complete devascularization of the treated area at the post-procedural CT. R(AZ:E) was determined dividing the ablation zone volume in mm3 by the amount of energy in kilojoules applied in each procedure and complications were reported.

RESULTS

Technical success was achieved in all the procedures. Mean R(AZ:E) was 0,75 ± 0,58. T-student test for patients with HCC and patients with metastasis about R(AZ:E) was significant (p = 0.03). The incidence of bilomas was lower for HCC (p = 0.022). One-month follow-up showed Complete Response (CR) in 44/46 (95,6%) patients; Three-six months follow-up demonstrated: CR in 43/46 (93.5%) cases and 12 months follow-up highlighted CR in 40/45 (88,9%) cases.

CONCLUSIONS

These results provide preliminary evidence of efficacy and safety of simultaneous liver MWA using two antennas, highlighting the importance of procedural indications.

Lung microwave ablation - an in vivo swine tumor model experiment to evaluate ablation zones

PURPOSE

To evaluate microwave ablation (MWA) algorithms, comparing pulsed and continuous mode in an in vivo lung tumor mimic model.

MATERIALS AND METHODS

A total of 43 lung tumor-mimic models of 1, 2 or 3 cm were created in 11 pigs through an intra-pulmonary injection of contrast-enriched minced muscle. Tumors were ablated under fluoroscopic and 3D-CBCT-guidance using a single microwave antenna. Continuous (CM) and pulsed mode (PM) were used. According to tumor size, 3 different algorithms for both continuous and pulsed mode were used. The ablation zones were measured using post-procedural 3D-CBCT and on pathologic specimens.

RESULTS

Two radiologists measured the ablation zones on CBCT and they significantly correlated with macroscopic and microscopic pathological findings: r = 0.75 and 0.74 respectively (p < 0.0001) (inter-observer correlation r = 0.9). For 1, 2 and 3 cm tumors mimics lesions (TMLs), mean maximal and transverse ablation diameters were 3.6 [Formula: see text] 0.3 × 2.2 [Formula: see text] 0.3 cm; 4.1 [Formula: see text] 0.5 × 2.6 [Formula: see text] 0.3 cm and 4.8 [Formula: see text] 0.3 × 3.2 [Formula: see text] 0.3 cm respectively using CM; And, 3.0 [Formula: see text] 0.2 × 2.1 [Formula: see text] 0.2 cm; 4.0 [Formula: see text] 0.4 × 2.7 [Formula: see text] 0.4 cm and 4.6 [Formula: see text] 0.4 × 3.2 [Formula: see text] 0.4 cm respectively for PM, without any significant difference except for 1 cm TMLs treated by PM ablation which were significantly smaller (p = 0.009) The sphericity index was 1.6, 1.6, 1.5 and 1.4, 1.5, 1.4 at 1, 2 and 3 cm for CM and PM respectively, p = 0.07, 0.14 and 0.13 for 1, 2 and 3 cm tumors mimics.

CONCLUSION

Microwave ablation for 1-3 cm lung tumors were successfully realized but with a moderate reproducibility rate, using either CM or PM. Immediate post ablation CBCT can accurately evaluate ablation zones.

A review of antenna designs for percutaneous microwave ablation

Microwave (MW) antenna is a key element in microwave ablation (MWA) treatments as the means that energy is delivered in a focused manner to the tumor and its surrounding area. The energy delivered results in a rise in temperature to a lethal level, resulting in cell death in the ablation zone. The delivery of energy and hence the success of MWA is closely dependent on the structure of the antennas. Therefore, three design criteria, such as expected ablation zone pattern, efficiency of energy delivery, and minimization of the diameter of the antennas have been the focus along the evolution of the MW antenna. To further improve the performance of MWA in the treatment of various tumors through inventing novel antennas, this article reviews the state-of-the-art and summarizes the development of MW antenna designs regarding the three design criteria.

Influence of interapplicator distance on multibipolar radiofrequency ablation during physiological and interrupted liver perfusion in an in vivo porcine model

Radiofrequency ablation (RFA) is a curative treatment option for early stage hepatocellular carcinoma (HCC). Vascular inflow occlusion to the liver (Pringle manoeuvre) and multibipolar RFA (mbRFA) represent possibilities to generate large ablations. This study evaluated the impact of different interapplicator distances and a Pringle manoeuvre on ablation area and geometry of mbRFA. 24 mbRFA were planned in porcine livers in vivo. Test series with continuous blood flow had an interapplicator distance of 20 mm and 15 mm, respectively. For a Pringle manoeuvre, interapplicator distance was predefined at 20 mm. After liver dissection, ablation area and geometry were analysed macroscopically and histologically. Confluent and homogenous ablations could be achieved with a Pringle manoeuvre and an interapplicator distance of 15 mm with sustained hepatic blood flow. Ablation geometry was inhomogeneous with an applicator distance of 20 mm with physiological liver perfusion. A Pringle manoeuvre led to a fourfold increase in ablation area in comparison to sustained hepatic blood flow (p < 0.001). Interapplicator distance affects ablation geometry of mbRFA. Strict adherence to the planned applicator distance is advisable under continuous blood flow. The application of a Pringle manoeuvre should be considered when compliance with the interapplicator distance cannot be guaranteed.

Large nearly spherical ablation zones are achieved with simultaneous multi-antenna microwave ablation applied to treat liver tumours

AIM

To investigate the shape and the volume of ablation zones obtained with microwave ablation (MWA) performed with multiple antennas in liver tumours.

MATERIALS AND METHODS

Tumour volume, number of antennas, size (long diameter (Dl), along the antenna axis; short diameter (Ds), perpendicular to the antenna axis; vertical diameter (Dv), vertical to both Dl and Ds) and shape (roundness index (RI); 1 corresponds to a sphere) of the ablation zone, ablation volume, and complications were evaluated.

RESULTS

Mean Dl, Ds, and Dv were 4.7 ± 1.4 cm, 3.9 ± 1.4 cm, and 3.8 ± 1.0 cm, respectively. Mean RIs (Ds/Dl, Dv/Dl, and Dv/Ds) were 0.83 ± 0.13, 0.83 ± 0.17, and 1.02 ± 0.23, respectively, without any difference between the mean RI obtained with the double (0.84 ± 0.01) and that with the triple-antenna (0.93 ± 0.13) approach (p = 0.25). Mean ablation volume was 41 ± 32 cm³ (vs. mean tumour volume 13 ± 10 cm³; range 1-40; p < 0.001). No complications were noted.

CONCLUSIONS

Simultaneous multi-antenna MWA of liver tumours results in large nearly spherical ablation zones.

KEY POINTS

• Simultaneous multi-antenna microwave ablation of liver tumours results in nearly spherical ablation zones. • The multi-antenna approach generates oversized ablation volumes compared with the target tumour volume. • The multi-antenna approach is safe.