How large is the periablational zone after radiofrequency and microwave ablation? Computer-based comparative study of two currently used clinical devices

Abstract

Purpose: To compare the size of the coagulation (CZ) and periablational (PZ) zones created with two commercially available devices in clinical use for radiofrequency (RFA) and microwave ablation (MWA), respectively. Methods: Computer models were used to simulate RFA with a 3-cm Cool-tip applicator and MWA with an Amica-Gen applicator. The Arrhenius model was used to compute the damage index (X). CZ was considered when X > 4.6 (>99% of damaged cells). Regions with 0.6<X < 2.1 were considered as the PZ (tissue that has undergone moderate sub-ablative hyperthermia). The ratio of PZ volume to CZ volume (PZ/CZ) was regarded as a measure of performance, since a low value implies achieving a large CZ while keeping the PZ small. Results: Ten-min RFA (51 W) created smaller periablational zones than 10-min MWA (11.3 cm 3 vs. 17.2À22.9 cm 3 , for 60À100 W MWA, respectively). Prolonging duration from 5 to 10 min increased the PZ in MWA more than in RFA (2.7 cm 3 for RFA vs. 8.3À11.9 cm 3 for 60À100 W MWA, respectively). PZ/CZ for RFA were relatively high (65À69%), regardless of ablation time, while those for MWA were highly dependent on the duration (increase of up to 25% between 5 and 10 min) and on the applied power (smaller values as power was raised, 102% for 60 W vs. 81% for 100 W, both for 10 min). The lowest PZ/CZ across all settings was 56%, obtained with 100 W-5 min MWA. Conclusions: Although RFA creates smaller periablational zones than MWA, 100 W-5 min MWA provides the lowest PZ/CZ.

Safety and efficacy of RFA versus MWA for T1a renal cell carcinoma: a propensity score analysis

“…Zhou et al, who compared 44 MWA with 347 RFAs and 46 cryoablations, did show a significant association between the RENAL nephrometry score and LTP for all patients [ 20 ]. Since MWA provides larger ablation zones with higher temperatures [ 26 ], size and central location would be less of an issue, only our results and literature suggest counter-wise.…”

Mathematical modeling of microwave liver ablation with a variable-porosity medium approach

“…and ΔE = 2.814 ×10 5 Jmol -1 [32].The D99 thermal damage contour is employed as in [8] to evaluate the thermal damage contour, i.e. the isoline Ω = 4.6 which corresponds to 99% of cell death probability according to the following equation:…”

“…Both the effective electric conductivity σ e and the relative permittivity ε r , are considered temperature dependent as in [8,42], so are defined as follows:…”

“…Table 1 shows the dielectric and thermal properties employed for healthy tissue, tumor, and blood [8,32,43].…”

“…the ablation zone does not completely cover the tumor), which is higher when ablative temperatures are not achieved [6]. As concerns this criticality, tumor zones where ablative temperatures do not occur, namely the periablational areas, can be interested by tumor regrowth [7], so this area must be minimized [8]. In this context, computational modeling of heat transfer in thermal ablation is relevant to predict the obtained ablation zone accurately, in order to improve current medical devices and protocols.…”