Patient Specific Simulation of HIFU Kidney Tumour Ablation

High Intensity Focussed Ultrasound (HIFU) is emerging as a non-invasive treatment for localised renal tumours. However, challenges remain in the delivery of the treatment to tumours at depth, with clinical results showing a variation in the ablation efficacy. One clinical trial conducted at the Churchill hospital, Oxford, to investigate the applicability of HIFU for renal tumour ablation found that in 4/10 patients less than 5% of the tumour volume was ablated successfully. The current study looks at the role tissue geometry has on the resulting focal pressure and focal heating. CT scans from 4 patients within the trial were selected, who experienced 70%, < 5%, < 5% and 95% ablation of the target tumour. The CT scans were segmented into bone, fat, kidney, and generic tissue. Full three-dimensional ultrasound simulations were carried out using k-Wave (an open source Matlab toolbox) and for three patients a tight focus was achieved in the kidney but peak pressures varied by 20%. While in the fourth patient there was significant fragmentation of the -6 dB focal volume due to the intervening ribcage. Thermal simulations were used to compare the temperature rise induced across the different patient models. For the three patients with a tight focus, the predicted 47°C iso-volume of the patient with 70% ablation was 2-3 times larger than the two patients with < 5% ablation. For the patient in which the ribcage resulted in focal fragmentation the thermal simulation predicted just a 1°C temperature rise.