Peri-tumoral Metallic Implants Reduce the Efficacy of Irreversible Electroporation for the Ablation of Colorectal Liver Metastases

PURPOSE

To evaluate the effect of peri-tumoral metallic implants (MI) on the safety and efficacy of percutaneous irreversible electroporation (IRE) of colorectal liver metastasis (CRLM).

MATERIALS AND METHODS

In this retrospective study, 25 patients (12 women, 13 men; MI: 13, no MI: 12) were treated for 29 CRLM. Patient characteristics, tumor location and size, treatment parameters and the presence of MI were evaluated as determinants of local tumor progression (LTP) with the competing risks model (univariate and multivariate analyses). Patient-specific computer models were created to examine the effect of the MI on the electric field used to induce IRE, probability of cell kill and potential thermal effects.

RESULTS

Patients had a median follow-up of 25 months, during which no IRE-related major complications were reported. Univariate analysis showed that tumor size (> 2 cm), probe spacing (> 20 mm) and the presence of MI (p < 0.05) were significant predictors of time to LTP, but only the latter was found to be an independent predictor on multivariate analysis (sub-hazard ratio = 6.5; [95% CI 1.99, 21.4]; p = 0.002). The absence of peri-tumoral MI was associated with higher progression-free survival at 12 months (92.3% [56.6, 98.9] vs 12.5% [2.1, 32.8]). Computer simulations indicated significant distortions and reduction in electric field strength near MI, which could have contributed to under-treatment of the tumor.

CONCLUSIONS

Peri-tumoral MI increases the risk of treatment failure following IRE of CRLM.

Electrochemotherapy of Spinal Metastases Using Transpedicular Approach-A Numerical Feasibility Study

Vertebral column is the most frequent site for bone metastases. It has been demonstrated in previous studies that bone metastases can be efficiently treated by electrochemotherapy. We developed a novel approach to treat spinal metastases, that is, transpedicular approach that combines electrochemotherapy with already established technologies for insertion of fixation screws in spinal surgery. In the transpedicular approach, needle electrodes are inserted into the vertebral body through pedicles and placed around the tumor. The main goal of our study was to numerically investigate the feasibility of the proposed treatment approach. Three clinical cases were used in this study—1 with a tumor completely contained within the vertebral body and 2 with tumors spread also to the pedicles and spinal canal. Anatomically accurate numerical models were built for all 3 cases, and numerical computations of electric field distribution in tumor and surrounding tissue were performed to determine the treatment outcome. Complete coverage of tumor volume with sufficiently high electric field is a prerequisite for successful electrochemotherapy. Close to 100% tumor coverage was obtained in all 3 cases studied. Two cases exhibited tumor coverage of >99%, while the coverage in the third case was 98.88%. Tumor tissue that remained untreated was positioned on the margin of the tumor volume. We also evaluated hypothetical damage to spinal cord and nerves. Only 1 case, which featured a tumor grown into the spinal canal, exhibited potential risk of neural damage. Our study shows that the proposed transpedicular approach to treat spinal metastases is feasible and safe if the majority of tumor volume is contained within the vertebral body. In cases where the spinal cord and nerves are contained within the margin of the tumor volume, a successful and safe treatment is still possible, but special attention needs to be given to evaluation of potential neural damage.

Determination of lethal electric field threshold for pulsed field ablation in ex vivo perfused porcine and human hearts

Introduction

Pulsed field ablation is an emerging modality for catheter-based cardiac ablation. The main mechanism of action is irreversible electroporation (IRE), a threshold-based phenomenon in which cells die after exposure to intense pulsed electric fields. Lethal electric field threshold for IRE is a tissue property that determines treatment feasibility and enables the development of new devices and therapeutic applications, but it is greatly dependent on the number of pulses and their duration.

Methods

In the study, lesions were generated by applying IRE in porcine and human left ventricles using a pair of parallel needle electrodes at different voltages (500-1500 V) and two different pulse waveforms: a proprietary biphasic waveform (Medtronic) and monophasic 48 × 100 μs pulses. The lethal electric field threshold, anisotropy ratio, and conductivity increase by electroporation were determined by numerical modeling, comparing the model outputs with segmented lesion images.

Results

The median threshold was 535 V/cm in porcine ((N = 51 lesions in n = 6 hearts) and 416 V/cm in the human donor hearts ((N = 21 lesions in n = 3 hearts) for the biphasic waveform. The median threshold value was 368 V/cm in porcine hearts ((N = 35 lesions in n = 9 hearts) cm for 48 × 100 μs pulses.

Discussion

The values obtained are compared with an extensive literature review of published lethal electric field thresholds in other tissues and were found to be lower than most other tissues, except for skeletal muscle. These findings, albeit preliminary, from a limited number of hearts suggest that treatments in humans with parameters optimized in pigs should result in equal or greater lesions.

Optimization of Transpedicular Electrode Insertion for Electroporation-Based Treatments of Vertebral Tumors

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.