Factors affecting tumor ablation during high intensity focused ultrasound treatment.

BACKGROUND/AIMS: High intensity focused ultrasound (HIFU) utilizes a targeted extracorporeal focused ultrasound beam to ablate neoplastic pancreatic tissue. We used an in vitro model to examine the effects of bone, metallic stents, plastic stents, metal plates, and cyst-like lesions on HIFU treatment. METHODS: HIFU was delivered to the phantom models implanted with foreign bodies, and the location, shape, and size of the ablated zones were evaluated. RESULTS: Bone and metallic plates reflected the ultrasound beam, shifting the ablation zone from the focal zone to the prefocal area. In the phantoms containing metal stent, plastic stent, and cyst, most of the ablative energy was reflected to the prefocal area by the surface, with the remainder penetrating through the phantom. The area of the ablated margins was significantly larger in size and volume than the intended focal ablation zone. CONCLUSIONS: During HIFU therapy, artificial or anatomical barriers could affect the direction of the ultrasound beams, shifting the ablation zone from the focal area to a prefocal site with a larger than expected ablation zone. These factors should be considered prior to HIFU treatment for pancreatic tumors because they could limit ablation success, in addition to causing complications.

EUS-guided radiofrequency ablation of the porcine pancreas.

BACKGROUND: EUS-guided radiofrequency ablation (EUS-RFA) could be used as an adjunct and effective alternative mode of treatment for unresectable locally advanced and nonmetastatic pancreatic adenocarcinoma. However, its translation into clinical practice has been restricted because of limited data and high procedure-related risk. OBJECTIVE: To evaluate the feasibility, efficacy, and safety of EUS-RFA in the normal porcine pancreas. DESIGN: Prospective, endoscopic, experimental study in a porcine model. SETTING: Tertiary-care referral center animal laboratory. PATIENTS: Animal study. INTERVENTION: EUS-RFA of the pancreas was attempted on 10 adult mini pigs. An 18-gauge endoscopic RFA electrode was used to puncture the body and tail of the pancreas, with an output power of 50 W for 5 minutes. MAIN OUTCOME MEASUREMENTS: The feasibility, efficacy, and safety of EUS-RFA. RESULTS: A spherical necrotic lesion surrounded by fibrous tissue localized in the pancreatic parenchyma was observed on histopathologic examination. The mean diameter of the ablated tissue was 23.0 ± 6.9 mm. No major procedure-related complications were noted, and all pigs survived without any distress behavioral pattern for 7 days until autopsy. LIMITATIONS: Small sample size with short-term observation and the lack of evaluation of the head of the pancreas. CONCLUSION: EUS-RFA of the pancreatic body and tail was feasible, effective, and relatively safe in a porcine model. More animal studies to assess damage to adjacent organs are required before human trials can be conducted.