F. Panzera

EUS-guided Nd:YAG laser ablation of normal pancreatic tissue: a pilot study in a pig model.

BACKGROUND Laser ablation with a neodymium:yttrium aluminum garnet (Nd:YAG) laser can achieve a high rate of complete tissue necrosis and has been applied as a minimally invasive, palliative option in hepatocellular carcinoma, liver metastasis in colorectal cancer, and malignant thyroid nodules. OBJECTIVE To assess the in vivo feasibility of EUS-guided laser ablation with an Nd:YAG laser of normal pancreatic tissue of a porcine model. DESIGN Prospective investigation. SETTING Hospital animal laboratory. SUBJECTS Eight pigs. INTERVENTIONS EUS-guided puncture of the pancreatic tail with a laser-beam fiber. An Nd:YAG laser (1.064 nm) was used, with an output power of 2 and 3 W and a total delivered energy of 500 and 1000 J in continuous mode. MAIN OUTCOME MEASUREMENTS The 24-hour follow-up of the pigs was focused on clinical and laboratory aspects. Results of histological studies of the pancreas were obtained 24 hours after the procedure on necroscopy tissue. RESULTS There were no technical limitations to the performance of the procedure. Tissue necrosis, localized in the pancreatic parenchyma, was observed in all animals on histological examination. The volume of ablation tissue ranged from a mean of 314 mm(3) to 483 mm(3). The ablation area ranged from a mean of 49 mm(2) to 80 mm(2). No major postprocedure complications were recorded, and all the pigs survived at 24 hours. LIMITATION Animal study. CONCLUSIONS EUS-guided laser ablation of the pancreas with an Nd:YAG laser is feasible in a porcine model.

Experimental assessment of CT-based thermometry during laser ablation of porcine pancreas.

Laser interstitial thermotherapy (LITT) is employed to destroy tumors in organs, and its outcome strongly depends on the temperature distribution inside the treated tissue. The recent introduction of computed tomography (CT) scan thermometry, based on the CT number dependence of the tissue with temperature, overcomes the invasiveness of other techniques used to monitor temperature during LITT. The averaged CT number (ROI = 0.02 cm(2)) of an ex vivo swine pancreas is monitored during LITT (Nd:YAG laser power of 3 W, treatment time: 120 s) at different distances from the applicator (from 4 to 30 mm). The averaged CT number shows a clear decrease during treatment: it is highest at 4 mm from the applicator (mean variation in the whole treatment of -0.256 HU s(-1)) and negligible at 30 mm, since the highest temperature increase is present close to the applicator (i.e., 45 °C at 4 mm and 25 °C at 6 mm). To obtain the relationship between CT numbers and pancreas temperature, the reference temperature was measured by 12 fiber Bragg grating sensors. The CT number decreases as a function of temperature, showing a nonlinear trend with a mean thermal sensitivity of -0.50 HU °C(-1). Results here reported are the first assessment of pancreatic CT number dependence on temperature, at the best of our knowledge. Findings can be useful to further investigate CT scan thermometry during LITT on the pancreas.

US-guided application of Nd:YAG laser in porcine pancreatic tissue: an ex vivo study and numerical simulation

BACKGROUND Laser ablation (LA) with a neodymium-doped yttrium aluminum garnet (Nd:YAG) laser is a minimally invasive approach able to achieve a high rate of complete tissue necrosis. In a previous study we described the feasibility of EUS-guided Nd:YAG pancreas LA performed in vivo in a porcine model. OBJECTIVE To establish the best laser setting of Nd:YAG lasers for pancreatic tissue ablation. A secondary aim was to investigate the prediction capability of a mathematical model on ablation volume. DESIGN Ex vivo animal study. SETTING Hospital animal laboratory. SUBJECTS Explanted pancreatic glands from 60 healthy farm pigs. INTERVENTION Laser output powers (OP) of 1.5, 3, 6, 10, 15, and 20 W were supplied. Ten trials for each OP were performed under US guidance on ex vivo healthy porcine pancreatic tissue. MAIN OUTCOME MEASUREMENTS Ablation volume (Va) and central carbonization volume (Vc) were measured on histologic specimens as the sum of the lesion areas multiplied by the thickness of each slide. The theoretical model of the laser-tissue interaction was based on the Pennes equation. RESULTS A circumscribed ablation zone was observed in all histologic specimens. Va values grow with the increase of the OP up to 10 W and reach a plateau between 10 and 20 W. The trend of Vc values rises constantly until 20 W. The theoretical model shows a good agreement with experimental Va and Vc for OP between 1.5 and 10 W. LIMITATIONS Ex vivo study. CONCLUSION Volumes recorded suggest that the best laser OP could be the lowest one to obtain similar Va with smaller Vc in order to avoid the risk of thermal injury to the surrounding tissue. The good agreement between the two models demonstrates the prediction capability of the theoretical model on laser-induced ablation volume in an ex vivo animal model and supports its potential use for estimating the ablation size at different laser OPs.

Theoretical assessment of principal factors influencing laser interstitial thermotherapy outcomes on pancreas

The influence of some therapy-relevant parameters on Laser Induced Interstitial Thermotherapy (LITT) outcomes on pancreas is assessed. The aim is to execute a sensitivity analysis for an optimal treatment strategy on in vivo pancreas. A numerical model based on Bioheat Equation has been implemented to assess the influence of laser settings (power P and energy E), applicator radius (rf) and optical properties (effective attenuation coefficient, μeff) on temperature (T) distribution. Effects on pancreas undergoing LITT have been evaluated with a twofold approach: 1) T rise and maximum T (Tmax) in tissue; 2) injured volumes (vaporized and coagulated ones). We consider parameters range in typical LITT values (P from 1.5 W to 6 W, E from 500 J to 1500 J, rf from 150 μm to 600 μm) and optical values reported in literature. Our analysis shows that, among others, P and μeff are the principal influencing factors of thermal effects on pancreas undergoing LITT: P should be carefully chosen by operator to obtain the desired injured volumes, while the accurate measurement of tissue optical properties is crucial to carry out a safe and controlled thermal therapy on pancreas.

Monitoring of temperature increase and tissue vaporization during laser interstitial thermotherapy of ex vivo swine liver by computed tomography

Laser interstitial thermotherapy (LITT) is a minimally invasive technique used to thermally destroy tumour cells. Being based on hyperthermia, LITT outcome depends on the temperature distribution inside the tissue. Recently, CT scan thermometry, based on the dependence of the CT number (HU) on tissue temperature (T) has been introduced during LITT; it is an attractive approach to monitor T because it overcomes the concerns related to the invasiveness. We performed LITT on nine ex vivo swine livers at three different laser powers, (P=1.5 W, P=3 W, P=5 W) with a constant treatment time t=200 s; HU is averaged on two ellipsoidal regions of interest (ROI) of 0.2 cm2, placed at two distances from the applicator (d=3.6 mm and d=8.7 mm); a reference ROI was placed away from the applicator (d=30 mm). The aim of this study is twofold: 1) to evaluate the effect of the T increase in terms of HU variation in ex vivo swine livers undergoing LITT; and 2) to estimate the P value for tissue vaporization. To the best of our knowledge, this is the first study focused on the HU variation in swine livers undergoing LITT at different P. The reported findings could be useful to assess the effect of LITT on the liver in terms of both T changes and tissue vaporization, with the aim to obtain an effective therapy.

Influence of FBG sensors length on temperature measures in laser-irradiated pancreas: Theoretical and experimental evaluation

Temperature distribution T(x,y,z,t) in tissue undergoing Laser-induced Interstitial Thermotherapy (LITT) plays a crucial role on treatment outcome. Theoretical and experimental assessment of temperature on ex vivo laser-irradiated pancreas is presented. The aim of this work is to assess the influence of thermometers dimensions on temperature measures during LITT. T(x,y,z,t) inside tissue is monitored by optical sensors, i.e., Fiber Bragg Gratings (FBGs): three FBGs with lengths of 10 mm and nine FBGs of 1 mm, at different distances (2 mm, 5 mm and 10 mm) and different quotes (0 mm, 2 mm and 4 mm) from the laser fiber tip are used. Theoretical punctual T(x,y,z,t) is averaged out on both 10 mm and 1 mm in order to compare numerical predictions with experimental data. Results demonstrate the influence of FBG length on T(x,y,z,t) measures. This phenomenon depends on the distance between sensor and applicator: it is particularly significant close to the applicator tip (2 mm) because of the high spatial T(x,y,z,t) gradient within the tissue. Both theoretical results and experimental ones show that just at a distance of 10 mm from the tip, differences between T(x,y,z,t) provided by FBGs of 10 mm and 1 mm are negligible.

P.03.9 FEASIBILITY OF EUS-GUIDE ND: YAG LASER ABLATION OF THE HEPATOCELLULAR CARCINOMA

Background and aim: We previously described a case of EUS-guided Nd:YAG (neodymium:yttrium-aluminium-garnet) LA of a HCC lesion located into the caudate lobe, not suitable for percutaneous approach. Aim is to confirm the feasibility of EUS-guided Nd:YAG LA of HCC in unsafe conditions for the percutaneous approach. Material and methods: Treatment was performed in 2 patients with multifocal HCC unsuitable for surgical resection or liver transplant. First one was affected by criptogenetic liver cirrhosis Child-Pugh A6 and lesion was site in the caudate lobe with huge ombelical vein and portal hypertension. The location of the lesion and the difficult ultrasonography visualization precluded percutaneous treatment. Second patient was affected by HCV and HIV cirrhosis Child-Pugh B9 with ascites and portal hypertension. Both patients underwent previous failed transarterial embolization (TACE) and RFA of lesions located into segment 1 and 3 respectively. Trans-gastric EUS-puncture was performed using a 22-gauge needle following the application of Doppler. A Nd:YAG laser with a wavelength of 1.064 nm was used. As previously described the treatment was planned taking into account the baseline volume of the lesions at EUS and the volume of necrosis that could be achieved in relation to the energy delivered. Results: Lesions were easier targeting through the lesser gastric curve. Application of Nd:YAG LA did not have any negative effect on the quality of the EUS images during the treatment and the whole treated area was occupied by an irregular and poorly defined echogenic zone at the end. The patients didn’t report any pain or abdominal discomfort after treatment and were discharged on the third postoperative day without complications. CT performed 24 hours after procedure showed the whole treated area replaced by an homogeneous, hypoattenuating, nonenhancing area. At 2 months follow-up clinical examination and blood analysis tests were normal. CT-scan showed uniform hypoattenuation without enhancement in the ablated zone and confirm the success to ablate the entire lesion. Conclusions: EUS-guided Nd:YAG LA of a HCC is feasible and safe in lesions in which the percutaneous approach is unsure. This promising results need to be confirmed in additional patients with lesions difficult to reach by conventional ablative methods or in patients whit compromised clinical conditions.