Percutaneous radiofrequency ablation is one of the most promising alternatives to open surgery for the treatment of liver
cancer. This operation is a minimally invasive procedure that consists in inserting a needle in targeted tissues that are
destroyed by heat. The success of such an operation mainly depends on the accuracy of the needle insertion, making it
possible to destroy the whole tumor, while avoiding damages on other organs and minimizing risks of a local recurrence.
We are developing a software that applies planning rules on patient-specific 3D reconstructions, in order to suggest relevant
options for the choice of a path to the tumor, and that displays various information allowing to adjust the final choice. In this
context we propose a method to compute automatically, quickly, and accurately, the possible insertion areas on the skin.
Within these areas, an insertion of the probe targeting the tumor respects the numerous strong (boolean) constraints required
for a radiofrequency ablation. Besides, these insertion zones define the research domain of the optimization process, taking
into account soft constraints to refine the solutions. They are also displayed on the skin of the virtual patient to inform the
physician about the different possibilities specific to each case, allowing him at the end of the automatic process, to modify
interactively the proposed strategy, with a real-time update of the related information. We discuss in this paper about the
importance of a precise delineation of these areas.
Radiofrequency ablation (RFA) has become an increasingly used technique in the treatment of patients with unresectable hepatic tumors. Evaluation of vascular architecture, post-RFA tissue necrosis prediction, and the choice of a suitable needle placement strategy using conventional radiological techniques remain difficult. In an attempt to enhance the safety of RFA, a 3D simulator and treatment planning tool, that simulates the necrosis of the treated area, and proposes an optimal placement for the needle, has been developed.
From enhanced spiral CT scans with 2 mm cuts, 3D reconstructions of patients with liver metastases are automatically generated. Virtual needles can be added to the 3D scene, together with their corresponding zones of necrosis that are displayed as a meshed spheroids representing the 60° C isosurface. The simulator takes into account the cooling effect of local vessels greater than 3mm in diameter, making necrosis shapes more realistic. Using a voxel-based algorithm, RFA spheroids are deformed following the shape of the vessels, extended by an additional cooled area. This operation is performed in real-time, allowing updates while needle is adjusted. This allows to observe whether the considered needle placement strategy would burn the whole cancerous zone or not.
Planned needle positioning can also be automatically generated by the software to produce complete destruction of the tumor with a 1 cm margin, with maximum respect of the healthy liver and of all major extrahepatic and intrahepatic structures to avoid. If he wishes, the radiologist can select on the skin an insertion window for the needle, focusing the research of the trajectory.