Objective: The aims of this study were to determine the electric field threshold that best fits the local response to irreversible electroporation (IRE) ablation of hepatic tumors as seen in follow-up MRI; to numerically evaluate the heat generating effect of IRE; and to demonstrate the utility of treatment planning to improve procedures in the future. Methods: 18 cases of hepatic tumors treated with IRE ablation were numerically reconstructed and treatment outcome was computed with a numerical treatment planning framework. Simulated ablation volumes were compared to ablation volumes segmented from 6-week follow-up MRI. Two cases with a high thermal component were selected for numerical optimization. Results: The best fit between segmented and simulated ablation zones was obtained at 900 V/cm threshold with the average absolute error of 5.6 ± 1.5 mm. Considerable heating was observed in 7/18 cases, where >50% of tumor volume experienced heating likely to cause thermal damage. In the selected two cases, thermal damage was eliminated with adjustment of applied voltages. Conclusion: Lesions visible on MRI 6 weeks post IRE represent areas that experienced an electric field of 900 V/cm or higher. This threshold is higher than previously reported for IRE of hepatic tumors. It is likely the 6-week follow-up period was too long and the ablation zone has already shrunk considerably, resulting in overestimation of the threshold. Significance : We developed a sophisticated method for validation of the numerical treatment planning framework. A future prospective study can be effectively designed based on the findings of this study.

Electrochemotherapy (ECT) and irreversible electroporation (IRE) are being investigated for treatment of hepatic tumours. The liver is a highly heterogeneous organ, permeated with a network of macro- and microvasculature, biliary tracts and connective tissue. The success of ECT and IRE depends on sufficient electric field established in whole target tissue; therefore, tissue heterogeneity may affect the treatment outcome. In this study, we investigate electroporation in the liver using a numerical mesoscale tissue model. We numerically reconstructed four ECT experiments in healthy porcine liver and computed the electric field distribution using our treatment planning framework. We compared the computed results with histopathological changes identified on microscopic images after treatment. The mean electric field threshold that best fitted the zone of coagulation necrosis was 1225 V/cm, while the mean threshold that best fitted the zone of partially damaged liver parenchyma attributed to IRE was 805 V/cm. We evaluated how the liver macro- and microstructures affect the electric field distribution. Our results show that the liver microstructure does not significantly affect the electric field distribution on the level needed for treatment planning. However, major hepatic vessels and portal spaces significantly affect the electric field distribution, and should be considered when planning treatments.

Electroporation-based treatments such as electrochemotherapy and irreversible electroporation ablation have sparked interest with respect to their use in medicine. Treatment planning involves determining the best possible electrode positions and voltage amplitudes to ensure treatment of the entire clinical target volume (CTV). This process is mainly performed manually or with computationally intensive genetic algorithms. In this study, an algorithm was developed to optimize electrode positions for the electrochemotherapy of vertebral tumors without using computationally intensive methods. The algorithm considers the electric field distribution in the CTV, identifies undertreated areas, and uses this information to iteratively shift the electrodes from their initial positions to cover the entire CTV. The algorithm performs successfully for different spinal segments, tumor sizes, and positions within the vertebra. The average optimization time was 71 s with an average of 4.9 iterations performed. The algorithm significantly reduces the time and expertise required to create a treatment plan for vertebral tumors. This study serves as a proof of concept that electrode positions can be determined (semi-)automatically based on the spatial information of the electric field distribution in the target tissue. The algorithm is currently designed for the electrochemotherapy of vertebral tumors via a transpedicular approach but could be adapted for other anatomic sites in the future.

Koncept ireverzibilne elektroporacije kot samostojne ablacijske metode je bil prvič predstavljen pred petnajstimi leti. Ireverzibilna elektroporacija predstavlja alternativo uveljavljenim termičnim ablacijskim metodam, saj mehanizem uničevanja celic ni pogojen z dvigom temperature. Zaradi ne-termičnega načina delovanja se zaenkrat uporablja predvsem v primerih, kjer uporaba termične ablacije ni mogoča zaradi nevarnosti poškodovanja bližnjih občutljivih anatomskih struktur ali kjer je učinkovitost ablacije zmanjšana zaradi odvajanja toplote (t. i. heat sink učinek). Trenutno se ireverzibilna elektroporacija v medicini uporablja predvsem za odstranjevanje globlje ležečih tumorjev, na primer v jetrih, prostati in ledvicah. V zadnjih letih je veliko zanimanja vzbudila tudi uporaba v srcu, in sicer za zdravljenje različnih motenj srčnega ritma. Ker je ablacija z ireverzibilno elektroporacijo relativno nova tehnologija, še vedno ni vzpostavljenih standardnih protokolov zdravljenja in postopkov načrtovanja zdravljenja. Numerične metode so nepogrešljivo orodje pri preučevanju fenomena elektroporacije in pri pripravi bolnikom prilagojenih načrtov zdravljenja. Prispevek obsega kratek pregled dosedanje uporabe ireverzibilne elektroporacije v kliničnem okolju, povzema prednosti in osvetljuje glavne izzive pri vpeljavi te obetavne ablacijske metode v klinično prakso.