Focused ultrasound for appendicular soft-tissue sarcomas: Three-dimensional targetability assessment – UROP Spring Symposium 2021

Focused ultrasound for appendicular soft-tissue sarcomas: Three-dimensional targetability assessment

Ibrahim Alnassar

Ibrahim Alnassar

Pronouns: He/Him

Research Mentor(s): Geoffrey Siegel, Assistant Professor
Research Mentor School/College/Department: Orthopaedic Surgery, Michigan Medicine
Presentation Date: Thursday, April 22, 2021
Session: Session 2 (11am – 11:50am)
Breakout Room: Room 10
Presenter: 5

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Focused ultrasound has been investigated as a noninvasive, nonionizing, repeatable treatment for appendicular soft tissue sarcomas (STSs), and standardized targetability criteria are needed to guide future clinical trials. Promising focused ultrasound modalities for STSs include high-intensity focused ultrasound (HIFU) and histotripsy. HIFU is typically MR-guided and uses an extracorporeal transducer to focus continuous, high-intensity ultrasound in a controlled manner, inducing thermal necrosis of a tumor. Thermal spread in HIFU can cause damage to critical anatomic structures located within 2 cm of the tumor. Histotripsy treatment is also delivered via an extracorporeal transducer but is ultrasound-guided and uses short pulses of high-intensity ultrasound to produce primarily mechanical tissue ablation. In contrast to HIFU, histotripsy treatments are tissue-selective (e.g. spare critical structures) based on differences in the mechanical properties of tumors and surrounding tissue. Previous targetability studies of focused ultrasound treatments for solid tumors have used exclusively 2D imaging and failed to account for potential tissue-selective effects. This study aims to develop a three-dimensional focused ultrasound targetability assessment for thigh STSs that includes consideration of tissue-selectivity. A subset of appendicular thigh STS patients from the Michigan Medicine Sarcoma Archive with sufficient pretreatment imaging is identified. Materialise Mimics software is then used to construct 3D renderings of tumors and significant surrounding nerves and blood vessels. Calculations of treatment parameters including distance from tumor edge to the nearest critical anatomic structure and depth from skin surface to tumor center are made using 2D MRI imaging and 3D reconstructions. Depth measurements in 3D use a calculated center of mass. The assessment finds that there are significant differences in measurements obtained from 2D imaging and 3D reconstructions, particularly measurements of tumor depth. Accounting for 3D anatomical detail permits a more standardized focused ultrasound targetability assessment for STSs and other solid tumors. We also identify a subset of STSs that would not be safely accessible to HIFU due to thermal spread but could potentially be treated using tissue-selective histotripsy. The risk of thermal spread is shown to limit the applicability of HIFU and illustrates the potential utility of histotripsy for tumors located near significant neurovascular structures.

Authors: Ibrahim Alnassar, Piush Sarkar, Lauren Mancia, Geoffrey Siegel
Research Method: Clinical Research

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