Interstitial ultrasound ablation of vertebral and paraspinal tumours: Parametric and patient-specific simulations

Abstract

Purpose Theoretical parametric and patient-specific models are applied to assess the feasibility of interstitial ultrasound ablation of tumours in and near the spine and to identify potential treatment delivery strategies. Methods 3D patient-specific finite element models (n=11) of interstitial ultrasound ablation of tumours associated with spine were generated. Gaseous nerve insulation and various applicator configurations, frequencies (3 and 7 MHz), placement trajectories, and tumour locations were simulated. Parametric studies with multilayered models investigated the impacts of tumour attenuation, tumour dimension, and the thickness of bone insulating critical structures. Temperature and thermal dose were calculated to define ablation (>240 equivalent minutes at 43°C (EM43°C)) and safety margins (<45°C & <6 EM43°C), and to determine performance and required delivery parameters. Results Osteolytic tumours (≤44 mm) encapsulated by bone could be successfully ablated with 7 MHz interstitial ultrasound (8.1-16.6 W/cm2, 120-5900 J, 0.4-15 min). Ablation of tumours (94.6-100% volumetric) 0-14.5 mm from the spinal canal was achieved within 3-15 min without damaging critical nerves. 3 MHz devices provided faster ablation (390 versus 930 s) of an 18 mm diameter osteoblastic (high bone content) volume than 7 MHz devices. Critical anatomy in proximity to the tumour could be protected by selection of appropriate applicator configurations, active sectors, and applied power schemas, and through gaseous insulation. Preferential ultrasound absorption at bone surfaces facilitated faster, more effective ablations in osteolytic tumours and provided isolation of ablative energies and temperatures. Conclusions Parametric and patient-specific studies demonstrated the feasibility and potential advantages of interstitial ultrasound ablation treatment of paraspinal and osteolytic vertebral tumours.

MRI-guided focused ultrasound ablation of lumbar medial branch nerve: Feasibility and safety study in a swine model

“…Additionally, a parametric patient-specific modeling of interstitial FUS ablation of vertebral tumors using a percutaneous 7 MHz ultrasound device [25] showed that tumors positioned at least 5 mm from the sensitive neural elements could be safely treated. When targeting the MB nerve using an extracorporeal FUS system, the cortical bone of the vertebral body and the transverse and superior articular processes are likely to serve as natural absorbers of ultrasound energy, preventing a significant portion of the far-field ultrasound beam from reaching the critical neural structures.…”

Review of Temperature Dependence of Thermal Properties, Dielectric Properties, and Perfusion of Biological Tissues at Hyperthermic and Ablation Temperatures

“…Computer simulations have increasingly been utilized in recent years as assistive tools for thermal treatments and are used as aid for planning, evaluating and optimizing therapies, and to minimize treatment risks preoperatively (20, 23, 28, 29, 32, 33, 37, 117–120). To obtain realistic models of thermal therapies it is important to use adequate mathematical functions to model the temperature dependence of tissue properties, or resort to using interpolation based on tabulated data if necessary.…”

Focused ultrasound for treatment of bone tumours

“…Expansion of indications for FUS inclusive of spinal treatments whether invasive [56] or non-invasive will significantly expand the number of patients 25 that may benefit from this treatment modality. Finally, additional randomized studies for malignant lesions using multimodality approaches including FUS are warranted.…”