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.

The Performance of Multiple Transgastric Procedures Using the Natural Orifice Transluminal Endoscopic Surgery Technique: Is Pure NOTES Satisfactory?

BACKGROUND/AIMS: Although several groups have demonstrated the usefulness of natural orifice transluminal endoscopic surgery (NOTES), there is still concern about frequent serious adverse events. We performed this study to determine the technical feasibility and safety of pure NOTES with a transgastric approach in a porcine model from the endoscopist's point of view. METHODS: Diagnostic peritoneoscopy, liver biopsy, salpingo-oophorectomy, and Fallopian tube ligation with a transgastric approach using a two-channel therapeutic endoscope were performed in 10 healthy female minipigs. These procedures were performed in two acute models and eight survival models in consecutive order. RESULTS: The technical success rate was 100% for peritoneoscopy (10/10), liver biopsy (5/5), salpingo-oophorectomy (10/10), and Fallopian tube ligation (10/10). Eight cases of adverse events occurred, including one case of splenic injury, one case of bleeding after liver biopsy, two cases of small bowel adhesion after salpingo-oophorectomy, two cases of hematoma at the salphingo-oophorectomy site, and two cases of partial dehiscence at the gastric closure site. The gastric puncture site was closed with seven to eight hemoclips in four cases and two hemoclips and an endoloop in four cases. CONCLUSIONS: The use of pure NOTES for peritoneoscopy, liver biopsy, salpingo-oophorectomy, and Fallopian tube ligation may be technically feasible, but considerable adverse events can occur during or after the procedure. Further studies utilizing specialized techniques overcome several limitations of pure NOTES are therefore necessary.