INTRODUCTION: Treating liver tumors by in situ ablation techniques like interstitial laser therapy (ILT)in combination with interrupted hepatic perfusion creates thermal lesions with complex geometry. The fact that they cannot yet be predicted or monitored on-line increases the risk of local recurrence. The aim of this study was to develop a computer-simulated 3-D irradiation model for predicting the ablation volume and to evaluate ILT in vivo with normal and interrupted perfusion.
MATERIAL/METHODS: Light and heat distribution in tissue was calculated by a Monte Carlo simulation. We first established a tissue database from optical parameters (human/animal/healthy/tumorous, n=120 samples). LITT parameters (30W, 15min, perfusion/ occlusion) were defined for the computer-model and a 3-D image of the coagulation volume was created. The simulation results (LongSim, TransSim, VolSim) were correlated to those in vivo in 15 domestic pigs (30-40 kg, i.v. anesthesia, median lap.). The animals were randomized into 3 groups: normal liver perfusion (ILTmono); interrupted perfusion by Pringle maneuver (ILTPringle); i.a. embolization by starch microspheres (ILTDSM). After intervention, the lesions were measured and the volumes (VolILT) were calculated.
RESULTS: Simulating the coagulation volume required 28.5 (23-27) minutes. Simulated or in vivo interrupted perfusion led to a 4.5-fold (DSM: 27.1 ccm ± 3.5) or 10-fold (Pringle: 60.2 ccm ± 2.2) increase in lesion volume in relation to ILTmono (6.3ccm ± 0.4). The deviation in the diameter between the simulation and in vivo data was a maximum of 3.1% ± 0.3 (ILTmono), 2.6% ± 0.3 (ILTPringle) and 15.6 % ± (ILTDSM), corresponding to 0.2 cm, 0.3 cm and 0.7 cm.
CONCLUSIONS: 1. The developed 3-D irradiation model showed very good agreement between simulated and in vivo data with prediction of the coagulation volume in ILT under normal and interrupted hepatic perfusion. 2. Due to the tridimensionality of the model, it is now possible for the first time to make a statement about the expected lesion geometry and the application parameters required for reliable tumor destruction during interstitial in situ ablation procedures.