In vitro Temperature Determination and Computer Simulation of the Temperature Distribution for optimal Planning and Control the Laser-induced Thermotherapy (LITT)

• Applicants: Dr. Norbert Siedow; Professor Dr. Thomas J. Vogl
• Subject Area: Nuclear Medicine, Radiotherapy, Radiobiology
• Term: from 2008 to 2016
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 64509286

Laser-induced thermotherapy (LITT) has been clinically established as a minimally invasive therapy for ablation of tumors and metastases in the liver tissue and other organs. In this method, the Nd:YAG laser is mostly used in continuous-wave (cw) mode. The laser photons are directly delivered into tumours and metastases through flexible glass fibers and are absorbed there. The resulted heat coagulates the tumor tissue and mortifies malignant cells. By use of the magnetic resonance imaging (MRI), the positioning of the laser applicators and a near real-time monitoring of the LITT is possible. A useful method for this purpose is the temperature monitoring during the treatment. With the help of a near real-time thermometry and computer simulation of the temperature distribution, the change of the thermal effect zone can be more exactly determined. A complete coagulation of the tumor tissue and a parallel protection of surrounding structures can be then achieved. In the proposed follow-up project, an MR thermometry software should be developed using the previous results. Based on the temperature coefficients of MR sequences, the software should allow for an automated temperature mapping during the LITT. To increase the signal-to-noise ratio (SNR) and consequently to enable more exact temperature calculation, the temperature coefficients of the MR sequences should be determined also for the 3 Tesla MRI as a part of the proposed project. Furthermore, the intra scan and inter scan artifacts should be explored and minimized for the MR thermometry with 3 Tesla. In addition, correction mechanisms for magnetic field drift and patient movements should be evaluated. In order to develop a software for the computer simulation of the temperature distribution, thermometry information was used in the last works to solve an inverse parameter identification problem. The unique solvability of the problem was proved and the solution was numerically obtained for the three-dimensional, rotationally symmetric case. However, for real three-dimensional cases, more efficient numerical algorithms should be developed. In the previous works, very simple geometrical models were used for the liver tissue with tumor, gall bladder and diverse blood vessels. In the proposed follow-up project, in order to make the computer simulation as close to reality as possible, the segmented image data of the liver tissue will be converted into a format, which is useable for the simulation. The operator should have the possibility of viewing the geometry from different angles to be then able to decide where the applicator has to be positioned. A virtual positioning of the applicators should be easily possible on the monitor. The software will be provided with a GUI that has all necessary input and output information and is easy to operate.

• DFG Programme: Research Grants