Thermal therapy of pancreatic tumours using endoluminal ultrasound: Parametric and patient-specific modelling

Abstract

Purpose To investigate endoluminal ultrasound applicator configurations for volumetric thermal ablation and hyperthermia of pancreatic tumors using 3D acoustic and biothermal finite element models. Materials and Methods Parametric studies compared endoluminal heating performance for varying applicator transducer configurations (planar, curvilinear-focused, or radial-diverging), frequencies (1–5 MHz), and anatomical conditions. Patient-specific pancreatic head and body tumor models were used to evaluate feasibility of generating hyperthermia and thermal ablation using an applicator positioned in the duodenal or stomach lumen. Temperature and thermal dose were calculated to define ablation (>240 EM43°C) and moderate hyperthermia (40–45 °C) boundaries, and to assess sparing of sensitive tissues. Proportional-integral control was incorporated to regulate maximum temperature to 70–80 °C for ablation and 45 °C for hyperthermia in target regions. Results Parametric studies indicated that 1–3 MHz planar transducers are most suitable for volumetric ablation, producing 5–8 cm3 lesion volumes for a stationary 5 minute sonication. Curvilinear-focused geometries produce more localized ablation to 20–45 mm depth from the GI tract and enhance thermal sparing (Tmax<42 °C) of the luminal wall. Patient anatomy simulations show feasibility in ablating 60.1–92.9% of head/body tumor volumes (4.3–37.2 cm3) with dose <15 EM43°C in the luminal wall for 18–48 min treatment durations, using 1–3 applicator placements in GI lumen. For hyperthermia, planar and radial-diverging transducers could maintain up to 8 cm3 and 15 cm3 of tissue, respectively, between 40–45 °C for a single applicator placement. Conclusions Modeling studies indicate the feasibility of endoluminal ultrasound for volumetric thermal ablation or hyperthermia treatment of pancreatic tumor tissue.

Endoluminal ultrasound applicators for MR‐guided thermal ablation of pancreatic tumors: Preliminary design and evaluation in a porcine pancreas model

“…In theoretical simulations of endoluminal ultrasound ablation of human pancreatic cancer, while pertaining to different anatomical conditions and tissue properties compared to porcine anatomy, it was demonstrated that endoluminal sonication through thinner luminal walls results in lower temperatures within the wall and minimizes the risk of thermal injuries. 31 As such, the risk of thermal damage would be reduced in humans due to the lower anticipated luminal wall thicknesses (2-3 mm). Similarly, in the experimental porcine setting there was likely an increased effective acoustic attenuation and absorption in the wall tissue due to the presence of food particles and/or gas bubbles in the mucosal layers, which could be reduced by flushing the interior stomach or GI lumen via lavage prior to treatment.…”

“…17 Transducer design changes that would enable better sparing of thick luminal walls include incorporating more tightly focused designs, with the focus depth at least 1 cm beyond the wall tissue. 31 Improving coupling between the applicator cooling balloon and luminal wall through tip steering, compression, or fixation mechanisms may also provide for consistent or enhanced luminal sparing.…”

Integration of deployable fluid lenses and reflectors with endoluminal therapeutic ultrasound applicators: Preliminary investigations of enhanced penetration depth and focal gain

“…The acoustic and thermal material properties of each tissue that were incorporated in the simulations are listed in Table . Water cooling (25 °C) was modeled on the interior of the stomach luminal surface, by using a convective heat flux boundary equation with a heat transfer coefficient of h = 500 W/m 2 /°C . The stomach wall was modeled as 3 mm thick .…”

“…30,34,35 Water cooling (25°C) was modeled on the interior of the stomach luminal surface, by using a convective heat flux boundary equation with a heat transfer coefficient of h = 500 W/m 2 /°C. 35 The stomach wall was modeled as 3 mm thick. 36 Dirichlet boundary conditions constrained the outer borders of the tissue boundary to 37°C.…”

A planning strategy for combined motion-assisted/gated MR guided focused ultrasound treatment of the pancreas

“…The acoustic properties of the pancreas were taken from [28]: density ¼ 1045 kg/m 3 , Thermal conductivity ¼ 0.51 W/m/ C, Specific Heat ¼ 3164 J/kg/ C, Perfusion rate¼ 4.5 kg/m 3 /s.…”