title: Development of an endoluminal high-intensity ultrasound applicator for image-guided thermal therapy of pancreatic tumors.
abstract: An ultrasound applicator for endoluminal thermal therapy of pancreatic tumors has been introduced and evaluated through acoustic/biothermal simulations andex vivoexperimental investigations. Endoluminal therapeutic ultrasound constitutes a minimally invinvasive conformal therapy and is compatible with ultrasound or MR-based image guidance. The applicator would be placed in the stomach or duodenal lumen, and sonication would be performed through the luminal wall into the tumor, with concurrent water cooling of the wall tissue to prevent its thermal injury. A finite-element (FEM) 3D acoustic and biothermal model was implemented for theoretical analysis of the approach. Parametric studies over transducer geometries and frequencies revealed that operating frequencies within 1-3 MHz maximize penetration depth and lesion volume while sparing damage to the luminal wall. Patient-specific FEM models of pancreatic head tumors were generated and used to assess the feasibility of performing endoluminal ultrasound thermal ablation and hyperthermia of pancreatic tumors. Results indicated over 80% of the volume of small tumors (~2 cm diameter) within 35 mm of the duodenum could be safely ablated in under 30 minutes or elevated to hyperthermic temperatures at steady-state. Approximately 60% of a large tumor (~5 cm diameter) model could be safely ablated by considering multiple positions of the applicator along the length of the duodenum to increase coverage. Prototype applicators containing two 3.2 MHz planar transducers were fabricated and evaluated inex vivoporcine carcass heating experiments under MR temperature imaging (MRTI) guidance. The applicator was positioned in the stomach adjacent to the pancreas, and sonications were performed for 10 min at 5 W/cm2applied intensity. MRTI indicated over 40°C temperature rise in pancreatic tissue with heating penetration extending 3 cm from the luminal wall.
authors.affiliation: Thermal Therapy Research Group, University of California San Francisco, 2340 Sutter Street, S341, San Francisco, CA 94115 ; Joint Graduate Program in Bioengineering, UC Berkeley and UC San Francisco.
authors.forename: Matthew S
authors.initials: MS
authors.lastname: Adams
authors.affiliation: Thermal Therapy Research Group, University of California San Francisco, 2340 Sutter Street, S341, San Francisco, CA 94115.
authors.forename: Serena J
authors.initials: SJ
authors.lastname: Scott
authors.affiliation: Thermal Therapy Research Group, University of California San Francisco, 2340 Sutter Street, S341, San Francisco, CA 94115.
authors.forename: Vasant A
authors.initials: VA
authors.lastname: Salgaonkar
authors.affiliation: Thermal Therapy Research Group, University of California San Francisco, 2340 Sutter Street, S341, San Francisco, CA 94115.
authors.forename: Peter D
authors.initials: PD
authors.lastname: Jones
authors.affiliation: Radiological Sciences Laboratory, Stanford University, 1201 Welch Road, Palo Alto, CA 94304.
authors.forename: Juan C
authors.initials: JC
authors.lastname: Plata-Camargo
authors.affiliation: Stanford Medical Center, 300 Pasteur Drive, Stanford, CA 94305.
authors.forename: Graham
authors.initials: G
authors.lastname: Sommer
authors.affiliation: Thermal Therapy Research Group, University of California San Francisco, 2340 Sutter Street, S341, San Francisco, CA 94115 ; Joint Graduate Program in Bioengineering, UC Berkeley and UC San Francisco.
authors.forename: Chris J
authors.initials: CJ
authors.lastname: Diederich
keywords: MR guided ultrasound; catheter-based ultrasound; endoluminal; pancreatic cancer; thermal modeling; thermal therapy; ultrasound ablation