Treatment planning for MRI-guided laser-induced interstitial thermotherapy of brain tumors--the role of blood perfusion.

MR techniques have been demonstrated to allow a reliable monitoring of laser-induced interstitial thermotherapy (LITT). However, an adequate on-line control of this coagulation technique requires an exact therapy planning. The latter is mandatory to interpret the MR-monitoring data correctly to guarantee a precise laser irradiation. Moreover, it is a prerequisite for on-line decisions if modifications of the therapeutic regimen are required. In this work, we present a new simulation technique for LITT planning. The model accounts for the specific geometry of the treatment site, the exact configuration of the applicator, and the optical and thermal properties of the tissue, including changes during the heating process. The simulation results were compared with MR scans of laser-induced lesions in three patients with World Health Organization (WHO) grade II astrocytoma. Special interest was directed toward the role of blood perfusion, which was studied parametrically. Good agreement between the simulation results and the MR data was found if the appropriate blood perfusion rates were taken into account. Thus, the model can generate valid therapy plans allowing a precise on-line control of laser irradiation using MR techniques. Neglecting adequate perfusion parameters resulted in substantial errors with respect to the prediction of the final laser lesion.