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Percutaneous Irreversible Electroporation of Surgically Unresectable Pancreatic Cancer:A Case Report

A 76-year-old African American male diagnosed with stage III (tumor/node/metastasis stages T4N0M0) unresectable pancreatic cancer secondary to vascular invasion was referred for percutaneous IRE after he refused chemotherapy or radiation. Computed tomography (CT) imaging (Fig 1) revealed a 4.1 *4.1 *3.5-cm mass with encasement of the celiac axis and origin of the superior mesenteric artery and occlusion of the extrahepatic portal vein and superior mesenteric vein. A whole-body staging CT scan demonstrated no metastatic disease.

Figure 1. Staging CT scan. (a) Superior aspect of low attenuation pancreatic carcinoma. Note occlusion of the splenic artery (arrow) within the mass. (b) Carcinoma (arrow) involves the portal vein confluence (asterisk) and superior mesenteric artery.

Percutaneous ablation was planned and performed as two ablative sessions to avoid the need for more than six probes to be placed at once. The patient was administered general anesthesia, and four 15-cm monopolar probes (Na- noknife; AngioDynamics, Latham, New York) were placed into the central and lateral aspect of the tumor under ultrasound (US) guidance in a square configuration, with average spacing of 1.8 cm. CT imaging with contrast medium was performed to evaluate needle postion relative to vessels and measure interprobe distance (Fig 2). All probes had 1 cm of electrode exposure, and one probe was placed by using a transhepatic approach. A 22-gauge spinal needle (Becton Dickinson, Franklin Lakes, New Jersey) was placed under US guidance into the gastrohepatic space to perform hydrodissection with sterile water.

Figure 2. IRE needle placement. Probes placed from anterior approach through the mass. A 22-g needle is also demonstrated between the pancreas and stomach for hydrodissection (arrow).

Six vectors (Fig 3) for pulse delivery were chosen with maximum and minimum interprobe distance of 2.3 and 1.4 cm, respectively. All pulses were administered in the absolute refractory period with use of electrocardiographic synchronization (AccuSync, Milford, Connecticut) to avoid triggering ventricular arrhythmia. IRE was performed with 90 treatment pulses delivered along each vector. Along one treatment vector, a “high current error” occurred when amperage exceeded 50 A, resulting in 70 of 90 pulses being delivered. The needles were pulled back 1 cm to perform an overlapping ablation with use of a similar protocol. After removal of all needles, CT imaging was performed, and the patient recovered uneventfully in the postanesthesia recovery unit. The patient was observed for 48 hours as an inpatient without incident. He did not require analgesic medications during his admission, and his diet was advanced over a period of 24 hours to a regular diet.

Figure 3. Graphic from Nanoknife software amended (arrows) to illustrate six vectors of pulse delivery.

After 2 weeks, the patient underwent a second IRE procedure targeting the untreated medial portion of the tumor, which was not treated during the initial intervention. The second ablation was performed by using a similar protocol with three probes. The probes were directed from lateral to medial and positioned under US guidance to confirm location relative to vascular structures. The patient was discharged 24 hours after the second ablation without pain or complications.

At 2-week clinical follow-up, the patient had mild, intermittent pain, without fatigue, fever, or other symptoms.Contrast-enhanced magnetic resonance (MR) imaging (Fig 4) was performed within 24 hours of each ablation and 30 days after the second ablation, and demonstrated an absence of enhancement within the expected ablation zone. Vasculature with the ablation zone, specifically the splenic artery and superior mesenteric artery, remained patent and unchanged from its preoperative appearance. Serum cancer antigen 19-9 levels decreased from 1,500 U/mL to 404U/mL at 30 days and 407 U/mL at 90 days after the ablation procedure. Positron emission tomography (PET)/CT imaging

(Fig 5) was performed 3 months after diagnosis and demonstrated a mild peripheral ring of fluorodeoxyglucose uptake. Although there was no evidence of residual tumor or nodal disease, a 1.5-cm liver metastasis was also identified on the 3-month PET/CT scan. Liver metastasis was

treated successfully with percutaneous RF ablation because the lesion was isolated from large vasculature. Chemotherapy with gemcitabine was then initiated. Two months after RF ablation, and 6 months after the diagnosis, MR imaging of the abdomen demonstrated no evidence of disease progression or recurrence. The cancer antigen 19-9 level decreased to 236 U/mL at 6 months.

Figure 4. MR image at 1 month after IRE procedure. (a) Superior aspect of tumor shows no residual enhancement of tumor, with maintained patency and appearance of the splenic artery (arrow). (b) At the level of the superior mesenteric artery, complete necrosis is also seen.

Figure 5. PET/CT image at 3 months. Smooth marginal uptake is seen, which is an expected finding after ablation. There is no focal residual disease in the pancreatic bed. Focal left hepatic uptake is not well seen on coronal projection.