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Open Access Publications from the University of California

Endoluminal Ultrasound Applicators for Thermal Therapy of Pancreatic Tumors

  • Author(s): Adams, Matthew
  • Advisor(s): Diederich, Chris J
  • et al.

The goals of this work are to investigate the feasibility of endoluminal ultrasound for delivering thermal ablation and hyperthermia to pancreatic tumors, and to perform a comprehensive design analysis of both practical and more intricate ultrasound applicator configurations suitable for endoluminal thermal therapy.

A platform for modeling the 3D acoustic, temperature, and thermal dose distributions generated from endoluminal ultrasound applicators and applied to pancreatic tumors and surrounding anatomy was developed. Performance ranges of practical endoluminal applicator designs were determined through comprehensive parametric analyses of applicator design and expected tissue parameters. Modeling studies in patient specific anatomies highlighted the capability of endoluminal ultrasound applicators positioned in the duodenum or stomach to deliver conformal and volumetric ablation or hyperthermia of pancreatic tumors with boundaries within 3-4 cm of the luminal wall while mitigating thermal damage to surrounding sensitive tissues.

A family of MR-compatible endoluminal ultrasound applicators, with distinct transducer configurations (~3 MHz, planar or curvilinear-focused) were designed, fabricated, and acoustically-characterized using bench-top methods. The capability of these applicators to be endogastrically delivered within the GI tract and to generate ablative temperature distributions in pancreatic tissue was evaluated in ex vivo and in vivo porcine studies, performed under MR navigation guidance and real-time treatment monitoring using MR temperature imaging. Preliminary acute studies in four in vivo pigs demonstrated the capabilities of the applicators to generate ablative temperature elevations of ~20-30 °C in pancreatic tissue at ~2-3 cm depths from the applicator, resulting in histologically-verified localized thermal lesions.

Novel endoluminal ultrasound applicator configurations that integrate deployable balloon-based acoustic reflector and fluid lens components were introduced and analyzed using theoretical modeling analysis and preliminary experimental validation. These applicators would be endoluminally delivered in a small profile, then expanded at the target luminal site to enhance the effective therapeutic aperture. A modeling framework, incorporating wave refraction and reflection at material interfaces was developed and used to perform comprehensive parametric studies for “end-firing” and “side-firing” design alternatives. Simulation studies illustrated the capability of these designs to achieve more localized thermal lesion formation and deeper penetration (up to 8-10 cm) as compared to conventional endoluminal ultrasound applicator designs.

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