Irreversible electroporation is considered to be a non-thermal ablative method that is feasible in pancreatic cancer treatment. However, the processes occurring in the ablation zone are not yet well known.

Pancreatic ductal adenocarcinoma has a very poor clinical prognosis, with an extremely low five-year survival rate of 5%. The majority of patients do not qualify for surgical treatment, which is usually the only potentially radical management option.

Locally advanced pancreatic cancer (LAPC) is characterised by wide infiltration of adjacent structures, including vessels, without distant metastases. There is a growing trend toward the application of ablative techniques like radiofrequency ablation (RFA), high intensity focused ultrasound (HIFU), microwave ablation (MWA), and radiation in inoperable pancreatic cancer. They offer cytoreduction, local tumour control and pain relief. However, thermal local ablations lead to the denaturation of ablated tissues and do not respect tubular and neural structures, thus presenting increased risk in the pancreatic region. Irreversible electroporation (IRE) is an increasingly common method in unresectable pancreatic cancer, resulting in cytoreduction followed by surgery and shows promising results in palliative care.

Irreversible electroporation performed under CT guidance; gas bubbles are seen around the electrodes, which proves the presence of thermal effects.

IRE produces electric pulses that cause damage to cell membranes, leading to apoptosis without the destruction of stroma. The preservation of stroma is the major advantage of IRE, as the pancreatic field is especially rich in structures like vessels, nerves, and bile and pancreatic ducts. This feature distinguishes IRE from thermal ablative procedures.

Despite general claims that IRE is a non-thermal method, some researchers have noticed signs of thermal effects after the procedure.

The aim of our study was to assess MRI examinations performed before and up to seven days after IRE to evaluate the early post-treatment changes in signal intensities within the ablation zone, with a special emphasis on thermal effects and vascularisation in the ablated zone.

We analysed MRI studies of 24 patients (10 female, 14 male, all aged 35–71) with LAPC during or shortly after chemotherapy. The standard IRE procedure was performed under general anaesthesia, percutaneously under CT-guidance or during open surgery. MR examinations were performed on 1.5T and 3T scanners in the above-mentioned time frame. The standard protocol for pancreas was applied, including T1WI, T2WI, DWI/ADC, and DCE with subtraction series. In patients where a CT-guided percutaneous procedure was performed, the signs of thermal effects were seen as small gas bubbles close to the electrodes. In MRI, they were present in 83.3% of patients as small, hypointense zones at the level of the electrodes’ placement.

The signal intensity in the ablated zone in T1WI FatSat images, after contrast media administration with subtraction, was in the range 0–6.25; this proves that all the vascular bed within the ablation zone was completely damaged. This complies with the results of the study of Fareja et al., showing that standard IRE procedures produce low temperatures and coagulation necrosis is not found within the ablation zone. This confirms that thermal effects are not a causative factor for devascularisation of the ablation zone.

Dr. Oliwia Kozak is a radiology resident at the University Clinical Centre in Gdańsk, Poland, and PhD researcher at the Medical University of Gdańsk.

My Thesis in 3 Minutes Session
MyT3 8 Oncologic Imaging

Thermal effect of irreversible electroporation in pancreatic cancer
O.W. Kozak, S. Hac, T. Gorycki, B. Brzeska, K. Skrobisz, J. Pienkowska, M. Szymanski, M. Studniarek; Gdańsk/PL

Read the full abstract in the ECR 2020 Book of Abstracts
Kozak O, et al. (2020) Thermal effect of irreversible electroporation in pancreatic cancer. Abstract MyT3 8-21 in: ECR 2020 Book of Abstracts. Insights Imaging 11, 34 (2020). DOI 10.1186/s13244-020-00851-0