Theoretical analysis and experimental evaluation of laser induced interstitial thermotherapy in ex vivo porcine pancreas

Laser-induced interstitial thermotherapy (LITT) hasbeen recently applied to pancreas in animal models for ablationpurpose. Assessment of thermal effects due to the laser–pancreatictissue interaction is a critical factor in validating the procedure feasibilityand safety. A mathematical model based on bioheat equationand its experimental assessment was developed. The LITTprocedure was performed on 40 ex vivo porcine pancreases, withan Nd:YAG (1064 nm) energy of 1000 J and power from 1.5 upto 10 W conveyed by a quartz optical fiber with 300 μm diameter.Six fiber Bragg grating sensors have been utilized to measuretemperature distribution as a function of time at fixed distancesfrom the applicator tip within pancreas undergoing LITT. Simulationsand experiments show temperature variations ΔT steeplydecreasing with distance from the applicator at higher power values:at 6 W, ΔT > 40 ◦C at 5 mm and ΔT ∼= 5 ◦C at 10 mm. ΔTnonlinearly increases with power close to the applicator. Ablatedand coagulated tissue volumes have also been measured and experimentalresults agree with theoretical ones. Despite the absenceof data in the current literature on pancreas optical parameters,the model allowed a quite good prediction of thermal effects. Theprediction of LITT effects on pancreas is necessary to assess laserdosimetry