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[EN] Purpose Multiple attempts have been made to manage the pancreatic stump and the pancreatic duct in order to reduce the rate of postoperative pancreatic fistula (POPF) after pancreaticoduodenectomy (PD), however radiofrequency-based technologies could help to achieve this goal. Previous encouraging clinical and experimental results support the use of endoluminal thermal ablation (ETHA) of the main pancreatic duct to reduce pancreatic exocrine secretion and hence POPF. We here describe our initial clinical experience with ETHA of the main pancreatic duct in two cases at high risk of POPF. Methods Two cases underwent PD for malignancy with a high risk of POPF (adenocarcinoma, obese patients, surgical difficulties with heavy intraoperative blood loss, soft pancreas or walled-off pancreatitis and a tight small pancreatic main duct). In both cases, ETHA of the main pancreatic duct was conducted intraoperatively just before Blumgart-type pancreatic-jejunal anastomosis using a ClosureFast catheter (Medtronic, Mansfield, MA, USA) normally used for varicose vein treatment (therefore an off-label use). Results Although a clear radiological POPF was detected in the second case, the clinical postoperative course in both cases was uneventful. Little pancreatic fluid collected in the abdominal drainage with low levels of amylase enzyme, confirming low exocrine pancreatic function. No other procedure-related complications were detected. Conclusion Endoluminal thermal ablation of the main pancreatic duct may be a feasible and safe technique to reduce the adverse effects of POPF after PD.

This is an Accepted Manuscript of an article published by Taylor & Francis in International Journal of Hyperthermia on Jan 01 2019, available online: http://www.tandfonline.com/10.1080/02656736.2019.1627585, [EN] Introduction: Endoluminal sealing of the pancreatic duct by glue or sutures facilitates the management of the pancreatic stump. Our objective was to develop a catheter-based alternative for endoluminal radiofrequency (RF) sealing of the pancreatic duct. Materials and methods: We devised a novel RF ablation technique based on impedance-guided catheter pullback. First, bench tests were performed on ex vivo models to tune up the technique before the in vivo study, after which endoluminal RF sealing of a similar to 10 cm non-transected pancreatic duct was conducted on porcine models using a 3 Fr catheter. After 30 days, sealing effectiveness was assessed by a permeability test and a histological analysis. Results: The RF technique was feasible in all cases and delivered similar to 5 W of power on an initial impedance of 308 +/- 60 ohm. Electrical impedance evolution was similar in all cases and provided guidance for modulating the pullback speed to avoid tissue sticking and achieve a continuous lesion. During the follow-up the animals rate of weight gain was significantly reduced (p < 0.05). Apart from signs of exocrine atrophy, no other postoperative complications were found. At necropsy, the permeability test failed and the catheter could not be reintroduced endoluminally, confirming that sealing had been successful. The histological analysis revealed a homogeneous exocrine atrophy along the ablated segment in all the animals. Conclusions: Catheter-based RF ablation could be used effectively and safely for endoluminal sealing of the pancreatic duct. The findings suggest that a fully continuous lesion may not be required to obtain complete exocrine atrophy.

[EN] Radiofrequency energy has been used both experimentally and clinically to manage the pancreatic remnant after distal pancreatectomies. Our goal was to determine whether endoluminal radiofrequency (RF) ablation of the main pancreatic duct in large animals would be more efficient than glue occlusion as an exocrine pancreatic atrophy-inducing procedure. Thirty-four Landrace pigs were assigned to either the transpapilar (n = 16) or transection (n = 18) groups. The transection implied the pancreas neck was severed. In each of these groups the remaining distal pancreatic duct was occluded either by RF or by glue. In the transpapilar group complete atrophy was observed in all the RF cases, while atrophy was incomplete in all the members of the glue subgroup. The failure rate of the main pancreatic duct (usually expressed by a pseudocyst) in the transection groups was dramatically higher in the glue subgroup than the RF subgroups (9 out of 9 and 1 out of 9, respectively) and postoperative mortality occurred only in the glue subgroup (3 out of 9). These results show the superiority of endoluminal RF ablation over glue for main pancreatic duct occlusion, as seen by the degree of atrophy and fewer postoperative pancreatic fistulas.

[EN] Purpose: To improve the computer modelling of radiofrequency ablation (RFA) by internally cooled wet (ICW) electrodes with added clinically oriented features. Methods: An improved RFA computer model by ICW electrode included: (1) a realistic spatial distribution of the infused saline, and (2) different domains to distinguish between healthy tissue, saline-infused tumour, and non-infused tumour, under the assumption that infused saline is retained within the tumour boundary. A realistic saline spatial distribution was obtained from an in vivo pig liver study. The computer results were analysed in terms of impedance evolution and coagulation zone (CZ) size, and were compared to the results of clinical trials conducted on 17 patients with the same ICW electrode. Results: The new features added to the model provided computer results that matched well with the clinical results. No roll-offs occurred during the 4-min ablation. CZ transversal diameter (4.10 +/- 0.19 cm) was similar to the computed diameter (4.16 cm). Including the tumour and saline infusion in the model involved (1) a reduction of the initial impedance by 10 - 20 ohm, (2) a delay in roll-off of 20 s and 70 - 100 s, respectively, and (3) 18 - 31% and 22 - 36% larger CZ size, respectively. The saline spatial distribution geometry was also seen to affect roll-off delay and CZ size. Conclusions: Using a three-compartment model and a realistic saline spatial distribution notably improves the match with the outcome of the clinical trials.

[EN] Metastases in the liver frequently grow as scattered tumor nodules that neither can be removed by surgical resection nor focally ablated. Previously, we have proposed a novel technique based on irreversible electroporation that may be able to simultaneously treat all nodules in the liver while sparing healthy tissue. The proposed technique requires increasing the electrical conductivity of healthy liver by injecting a hypersaline solution through the portal vein. Aiming to assess the capability of increasing the global conductivity of the liver by means of hypersaline fluids, here, it is presented a mathematical model that estimates the NaCl distribution within the liver and the resulting conductivity change. The model fuses well-established compartmental pharmacokinetic models of the organ with saline injection models used for resuscitation treatments, and it considers changes in sinusoidal blood viscosity because of the hypertonicity of the solution. Here, it is also described a pilot experimental study in pigs in which different volumes of NaCl 20% (from 100 to 200mL) were injected through the portal vein at different flow rates (from 53 to 171 mL/minute). The in vivo conductivity results fit those obtained by the model, both quantitatively and qualitatively, being able to predict the maximum conductivity with a 14.6% average relative error. The maximum conductivity value was 0.44second/m, which corresponds to increasing 4 times the mean basal conductivity (0.11second/m). The results suggest that the presented model is well suited for predicting on liver conductivity changes during hypertonic saline injection.

Purpose: To evaluate the impact of using monopolar thermal coagulation based on radiofrequency (RF) currents on intraoperative blood loss during liver resection. Materials and methods: A prospective randomized controlled trial was planned. Patients undergoing hepatectomy were randomized into two groups. In the Control group (n=10), hemostasis was obtained with a combination of stitches, vessel-sealing bipolar RF systems, sutures or clips. In the monopolar radiofrequency coagulation (MRFC) group (n=18), hemostasis was mainly obtained using an internally cooled monopolar RF electrode. Results: No differences in demographic or clinical characteristics were found between groups. Mean blood loss during liver resection in the Control group was more than twice that of the MRFC group (556±471 ml vs. 225±313 ml, p=0.02). The adjusted mean bleeding/transection area was also significantly higher in the Control group (7.0±3.3 ml/cm2 vs. 2.8±4.0 ml/cm2 , p=0.006). No significant differences were observed in the rate of complications between the groups. Conclusions: The findings suggest that the monopolar electrocoagulation created with an internally-cooled RF electrode considerably reduces intraoperative blood loss during liver resection.

Background: Spread hepatic tumours are not suitable for treatment either by surgery or conventional ablation methods. The aim of this study was to evaluate feasibility and safety of selectively increasing the healthy hepatic conductivity by the hypersaline infusion (HI) through the portal vein. We hypothesize this will allow simultaneous safe treatment of all nodules by irreversible electroporation (IRE) when applied in a transhepatic fashion. Material and methods: Sprague Dawley (Group A, n = 10) and Athymic rats with implanted hepatic tumour (Group B, n = 8) were employed. HI was performed (NaCl 20%, 3.8 mL/Kg) by trans-splenic puncture. Deionized serum (40 mL/Kg) and furosemide (2 mL/Kg) were simultaneously infused through the jugular vein to compensate hypernatremia. Changes in conductivity were monitored in the hepatic and tumour tissue. The period in which hepatic conductivity was higher than tumour conductivity was defined as the therapeutic window (TW). Animals were monitored during 1-month follow-up. The animals were sacrificed and selective samples were used for histological analysis. Results: The overall survival rate was 82.4% after the HI protocol. The mean maximum hepatic conductivity after HI was 2.7 and 3.5 times higher than the baseline value, in group A and B, respectively. The mean maximum hepatic conductivity after HI was 1.4 times higher than tumour tissue in group B creating a TW to implement selective IRE. Conclusions: HI through the portal vein is safe when the hypersaline overload is compensated with deionized serum and it may provide a TW for focused IRE treatment on tumour nodules.

Purpose: To assess the capacity of two methods of surgical pancreatic stump closure in terms of reducing the risk of pancreatic fistula formation (POPF): radiofrequencyinduced heating versus mechanical stapler. Materials and Methods: Sixteen pigs underwent a laparoscopic transection of the neck of the pancreas. Pancreatic anastomosis was always avoided in order to work with an experimental model prone to pancreatic fistula formation (POPF). Pancreatic stump closure was conducted either by stapler (ST Group, n=8) or radiofrequency energy (RF Group, n=8). Both groups were compared for incidence of POPF and histopathologic alterations of the pancreatic remnant. Results: Six animals (75%) in the ST Group and one (14%) in the RF Group were diagnosed of POPF (p=0.019). One animal in the RF Group and three animals in the ST Group had a pseudocyst in close contact with both pancreas stumps. On day 30 postoperative, almost complete atrophy of the exocrine distal pancreas was observed when the main pancreatic duct was efficiently sealed. Conclusions: Our findings suggest that RF-induced heating is more effective at closing the pancreatic stump than mechanical stapler and leads to the complete atrophy of the distal remnant pancreas.

Irreversible electroporation is a fast-growing liver ablation technique. Although safety has been well documented in small ablations, our aim is to assess its safety and feasibility when a large portion of liver is ablated. Eighty-seven mice were subjected to high voltage pulses directly delivered across parallel plate electrodes comprising around 40% of mouse liver. One group consisted in 55 athymicnude, in which a tumor from the KM12C cell line was grown and the other thirty-two C57-Bl6 nontumoral mice. Both groups were subsequently divided into subsets according to the delivered field strength (1000V/cm, 2000V/cm) and whether or not they received anti-hyperkalemia therapy. Early mortality (less than 24hours post-IRE) in the 2000V/cm group was observed and revealed considerably higher mean potassium levels. In contrast, the animals subjected to a 2000V/cm field treated with the anti-hyperkalemia therapy had higher survival rates (OR=0.1, 95%CI=0.02–0.32, p<0.001). Early mortality also depended on the electric field magnitude of the IRE protocol, as mice given 1000V/cm survived longer than those given 2000V/cm (OR=4.7, 95%CI=1.8–11.8, p=0.001). Our findings suggest that ionic disturbances, mainly due to potassium alterations, should be warned and envisioned when large volume ablations are performed by IRE.

Purpose: To assess by means of computer simulations whether the heat sink effect inside a large vessel (portal vein) could protect the vessel wall from thermal damage close to an internally cooled electrode during radiofrequency (RF)-assisted resection. Methods: First, in vivo experiments were conducted to validate the computational model by comparing the experimental and computational thermal lesion shapes created around the vessels. Computer simulations were then carried out to study the effect of different factors such as device-tissue contact, vessel position, and vessel-device distance on temperature distributions and thermal lesion shapes near a large vessel, specifically the portal vein. Results: The geometries of thermal lesions around the vessels in thein vivo experiments were in agreement with the computer results. The thermal lesion shape created around the portal vein was significantly modified by the heat sink effect in all the cases considered. Thermal damage to the portal vein wall was inversely related to the vessel-device distance. It was also more pronounced when the device-tissue contact surface was reduced or when the vessel was parallel to the device or perpendicular to its distal end (blade zone), the vessel wall being damaged at distances less than 4.25 mm. Conclusions: The computational findings suggest that the heat sink effect could protect the portal vein wall for distances equal to or greater than 5 mm, regardless of its position and distance with respect to the RF-based device. © 2014 American Association of Physicists in Medicine.