Planning of anatomical resections and in situ ablations in oncologic liver surgery

GPU-based real-time approximation of the ablation zone for radiofrequency ablation

Percutaneous radiofrequency ablation (RFA) is becoming a standard minimally invasive clinical procedure for the treatment of liver tumors. However, planning the applicator placement such that the malignant tissue is completely destroyed, is a demanding task that requires considerable experience. In this work, we present a fast GPU-based real-time approximation of the ablation zone incorporating the cooling effect of liver vessels. Weighted distance fields of varying RF applicator types are derived from complex numerical simulations to allow a fast estimation of the ablation zone. Furthermore, the heat-sink effect of the cooling blood flow close to the applicator's electrode is estimated by means of a preprocessed thermal equilibrium representation of the liver parenchyma and blood vessels. Utilizing the graphics card, the weighted distance field incorporating the cooling blood flow is calculated using a modular shader framework, which facilitates the real-time visualization of the ablation zone in projected slice views and in volume rendering. The proposed methods are integrated in our software assistant prototype for planning RFA therapy. The software allows the physician to interactively place virtual RF applicator models. The real-time visualization of the corresponding approximated ablation zone facilitates interactive evaluation of the tumor coverage in order to optimize the applicator's placement such that all cancer cells are destroyed by the ablation.

Trajectory optimization for the planning of percutaneous radiofrequency ablation of hepatic tumors

Radiofrequency ablation is increasingly used in the treatment of hepatic tumors. Planning the percutaneous intervention is essential and particularly difficult. In this paper, we focus on an automated computation of optimal needle insertion in computer-assisted surgery with 3D visualization. First, we review our method which delineates on the skin of a virtual patient the candidate zones for needle insertion, i.e., those which allow safe access to the tumor. In each case, we look for the trajectory that minimizes the volume of burnt tissue. Secondly, we introduce a quasi-exhaustive method that allies sampling and certified minimization to form a strong argument for the accuracy of our results. We also compare results of applying both methods on 7 representative reconstructed patient cases.