High intensity focussed ultrasound treatment planning for renal tumour ablation

Thesis

The use of High Intensity Focussed Ultrasound for the thermal ablation of renal tumours provides a completely non-invasive method for treatment, which is advantageous for patients who are not eligible for surgery due to co-morbidity issues. However, clinical trials have shown variable results with challenges to the delivery of the ultrasound beam related to the intervening tissue layers. The use of patient-specific models is investigated as a means to provide a treatment planning step to aid clinicians in the choice of the transducer’s position and ultrasound power for the treatment.

CT scans from patients treated in a clinical trial were segmented into bone, muscle and fat. Then patient-specific acoustic simulations were undertaken using the time domain acoustic solver software k-Wave. Patient-to-patient anatomical variability yielded differences of up to 154 W in the acoustic powers required for successful renal tumour ablation.

To find an optimal placement for the transducer, back-propagation acoustic simulations were undertaken. A virtual source was placed within the tumour with the receiver surface representing the potential transducer locations. The complex pressure received over the transducer surface was used to predict the optimal placement.

The present thesis also considers the sensitivity of the model to speed of sound variations. There was a significant impact on the focal pressure due to the relative change in speed of sound between fat and muscle. For the patient model tested there was a > 20% change in maximum pressure for variations of 4% and 7% in the speed of sound of muscle and fat respectively.

In conclusion, patient-specific acoustic modelling was successfully used to evidence the patient to patient variability in power requirements for renal tumour ablation as well as the significance of transducer placement for the individual patient. This in turn explains the significant variability in ablation outcomes achieved in clinical studies to date, and emphasizes the need for careful patient-specific treatment planning if renal ablation is to be adopted clinically.

Authors: Abbas, MA

• DOI: 10.5287/ora-bmbjnemra
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: cancer therapeutics; HIFU tumour ablation; treatment planning; high intensity focussed ultrasound
• Subjects: Cancer therapeutics; High-intensity focused ultrasound