A simulation study of the HIFU ablation process on lung tumours, showing consequences of atypical acoustic properties in flooded lung

Abstract

Recent work has shown that One Lung Flooding (OLF) enables acoustic access to central lung tumours which can be used for non-invasive ablation using therapeutic ultrasound (HIFU). Therefore acoustic properties of flooded lung as a saline-tissue compound was determined in earlier work, which revealed that atypical acoustical condition in lung exists. Their influence on the HIFU ablation process under aspects of clinical requirements has to be investigated before clinical introduction. For this study a MATLAB based ultrasound simulation tool and a customized bioheat solver were used to determine the temporal course of HIFU induced heating with the corresponding ablation zones. This work revealed that due to the low attenuation in flooded lung the heat induction and therefore the lesion size in lung tumours is enhanced. However, HIFU raster ablation schemes should only be used for benign tumours and the volumetric ablation scheme for malignancies. A minimum power density of 0.1Wcm^-3 is required during volumetric ablation to radical ablate lung tumours. The simulations indicate that up to 3 T1 (∅ 3cm) tumours with a sufficient margin (>3mm) can be ablated during one flooding session. The ablation margin is dependent upon perfusion, intra-lobular temperature, as well as ablation temperature, and can be adjusted within range of 2-6mm depending on nodule size. The acoustic conditions in flooded lung are beneficial for thermal HIFU ablation in lung but require an individualized HIFU treatment planning.

Keywords: Bioheat simulation; Focal salvage therapy; HIFU; Lung tumour; One Lung Flooding.