Search

Background and Objectives Proliferation and synthesis of hepatocellular tissue after tissue damage are promoted by specific growth factors such as hepatic tissue growth factor (HGF) and connective growth factor (CTGF). Laser-induced thermotherapy (LITT) for the treatment of liver metastases is deemed to be a parenchyma-saving procedure compared to hepatic resection. The aim of this study was to compare the impact of LITT and hepatic resection on intrahepatic residual tumor tissue and expression levels of mRNA HGF/CTGF within liver and tumor tissue. Study Design/Materials and Methods Two independent adenocarcinomas (CC531) were implanted into 75 WAG rats, one in the right (untreated tumor) and one in the left liver lobe (treated tumor). The left lobe tumor was treated either by LITT or partial hepatectomy. The control tumor was submitted to in-situ hybridization of HGF and CTGF 24–96 hours and 14 days after intervention. Results Volumes of the untreated tumors prior to intervention were 38±8 mm3 in group I (laser), 39 ± 7 mm3 in group II (resection), and 42 ± 12 mm3 in group III (control) and did not differ significantly (P > 0.05). Fourteen days after the intervention the mean tumor±SEM volume of untreated tumor in group I (laser) [223 ± 36] was smaller than in group II (resection) [1233.28 ± 181.52; P

Background and Objectives The therapeutic application of laser light is a promising alternative to surgical resection of colorectal liver metastases. The extent of tumor destruction achieved by this strategy depends primarily on light distribution in the target tissue. Knowledge about optical properties is necessary to predict light distribution in the tissue for careful irradiation planning. The aim of this study was to compare the optical behavior of healthy colon tissue with that of colorectal carcinomas and their hepatic metastases in the native and coagulated state in order to test the effect of malignant degeneration, metastasis, and thermal coagulation on optical parameters. Materials and Methods Ninety tissue samples were taken from patients with a colorectal carcinoma and concomitant liver metastases: healthy colon tissue (n = 30); colon carcinoma (n = 30); liver metastases (n = 30). Optical properties were measured according to the single integrating sphere principle in the native state and after thermal coagulation in the wavelength range of 800–1,100 nm and analyzed by inverse Monte Carlo simulation. Results The highest optical penetration depth for all tissue types was obtained at the end of the spectral range investigated. The highest penetration depths of 4.13 mm (healthy colon), 7.47 mm (colon carcinoma tissue), and 4.08 (liver metastases) were at 1,060 nm, although the values decreased significantly after thermal coagulation. Comparing healthy colon-to-colon carcinoma always revealed a significantly lower absorption and scattering coefficient in the tumor tissue. This resulted in a higher optical penetration depth of the laser light in the colon carcinoma tissue (P

Background and Objectives In contrast to hepatic resection, thermally destroyed autologous tumor cells remain in situ after laser-induced thermotherapy (LITT). The aim of the study was to evaluate the effect of LITT and hepatic resection on the immune response to residual intrahepatic tumor tissue and the growth of untreated liver metastases. Study Design/Materials and Methods Two independent adenocarcinomas (CC531) were implanted into 60 WAG rats, one in the right (control tumor) and one in the left liver lobe (treated tumor). The left lobe tumor was treated either by LITT or partial hepatectomy. The control tumor was submitted to further investigation 24 hours, 96 hours, 7 days, and 10 days after treatment. Results Ten days after treatment, control tumor volumes were 296±46 mm_ after LITT and 1,181±192 mm_, 1,387±200 mm_ after hepatic resection and no treatment, respectively (P

Background and Objective The aim of this study was to evaluate the accuracy of Gd-DTPA MRI in the detection of recurrent tumor after laserinduced thermotherapy (LITT) of experimental liver metastases. Study Design/Materials and Methods LITT was performed at different energy levels in VX-2 tumor-bearing rabbits (n = 80). MRI and histology were placed at 0, 24, 96 hours, and 14 days. Signal intensities were calculated of the transition between thermally damaged and undamaged tissue (transition zone = TZ) and of the surrounding tissue (reference zone = RZ). Results Tumor recurrence was seen in 47 animals. At 24 hours sensitivity, specificity and accuracy was 92, 100, and 95% in TZ and 23, 100, and 50% in RZ. At 14 days sensitivity, specificity and accuracy was 100, 11, and 60% in TZ and 100, 89, and 95% in RZ. Conclusions Recurrence is best excluded in TZ at 24 hour and in RZ at 14 day with an accuracy up to 95%. Lasers Surg. Med. 30:280–289, 2002. © 2002 Wiley-Liss, Inc.

A newly developed diffusing laser applicator was examined for interstitial laser coagulation (ILC) of liver tumours. The applicator consisted of a matted quartz core and a quartz glass dome, also matted on its inner surface and sealed to the fibre. The applicator provided a homogeneous light intensity distribution over an active length of about 20 mm. Lesions were created in an ex-vivo porcine liver model using a Nd-YAG laser comparing the new diffusing tip with a Ringmode(®)-ITT applicator in order to find optimal laser parameters and damage thresholds. The lesions were investigated using macroscopic size measurement, volume calculation and histological examination (HE, NADPH-dehydrogenase). The damage threshold of the diffusing tip was 6 W at 14 min exposure time whereas the Ringmode(®)-ITT applicator had its limit at 5 W and 12 min exposure. Comparing various exposure times showed that treatment over a time of more than 840 s did not significantly increase the lesion volume. At 5 W and 720 s the mean lesion volume was 6.9±1.1 cm(3) with the diffusing tip and 6.3±0.6 cm(3) with the Ringmode(®)-ITT applicator, both having a slight ellipsoidal shape. Hence, the created lesions were not significantly different for both applicators when the same laser parameters were applied. On the other hand, the new diffusing tip had a higher damage threshold and was therefore capable of producing maximal coagulation volumes of up to 7.9±0.5 cm(3) at 5 W and 20 min. The experiments showed that lesions with a dimension of 31×22 mm can be achieved with the diffusing applicator which seem suitably sized for treating small human liver metastases in a single laser session.

Background and Objective Laser induced thermotherapy (LITT) is a promising treatment for irresectable liver tumors. For predicting the effects of laser applications and optimizing irradiation planning in LITT, knowledge about light distribution in tissue, optical tissue properties (absorption, scattering, anisotropy, penetration depth) and their changes due to thermal denaturation is indispensable. Study Design/Materials and Methods The optical parameters in healthy porcine liver were determined in the native state and after thermal coagulation using a double integrating sphere system in the wavelength range of 400–2400 nm. Results Optical parameters showed significant fluctuations in the examined wavelength range mainly due to the water and hemoglobin content in the tissue. The greatest optical penetration depth of 7.46 mm was achieved at 1070 nm. After thermal coagulation, a clear increase in scattering and a slight decrease in absorption was found, which results in a decreased optical penetration depth. Conclusions In order to ensure a safe and effective procedure, an adjustment of the laser power to the decreasing penetration depth is recommended during therapy. These results provide a better understanding of laser-tissue interaction and may be helpful to investigators in the field of light dosimetry in liver tissue. Lasers Surg. Med. 29:205–212, 2001. © 2001 Wiley-Liss, Inc.

Purpose: The aim of this study was to determine the energy (J/mm3 tumor volume) and temperature required for a complete laser-induced thermotherapy (LITT) of experimental liver tumors, and to find out causes and areas of local recurrence followed by incomplete treatment. Methods: In VX-2 tumor-bearing rabbits LITT was performed using neodymium:yttrium-aluminum-garnet (Nd:YAG) laser (1064 nm) with a diffuser-tip applicator and a temperature feedback system. The animals were randomized into four groups (n = 20) that differed in the target temperature at the tumor border as follows: 45°C, 50°C, 55°C and 60°C. The target temperature was held for 10 min constant. Histologic examination (hematoxylin and eosin [H&E], nicotinamide adenine dinucleotide phosphate [NADPH]-dehydrogenase) was performed at 0 h, 24 h, 96 h, and 14 days after LITT. Results: The pretreatment tumor volume of 2191 ± 61 mm3 was the same for all groups (p > 0.05). Energy up to target temperature and total energy required, lesion size, and the rate of incomplete tumor ablation (recurrences) are listed below (ap < 0.05, Kruskal-Wallis test). Histologically, two forms of local recurrences could be differentiated intralesionary and extralesionary. Conclusions: To achieve complete in situ ablation under the given conditions, it is necessary to apply laser energy of 3 J/mm3 tumor volume. A minimum temperature of 60°C on the tumor border presumed an application of 10 min. Recurrence was found outside the coagulation zone (extralesionary) and in high vascularized areas within the coagulation zone (intralesionary).

Background and Objective Laser-induced thermotherapy (LITT) is a promising treatment for irresectable liver tumors. To predict the effects of laser applications and to optimize treatment planning in LITT, it is essential to gain knowledge about light distribution in tissue, tissue optical properties (absorption, scattering, anisotropy, penetration depth), and their continuous changes during therapy. Study Design/Materials and Methods Measurements of optical properties were performed with a double integrating-sphere system and a laser diode (830 nm). Porcine liver tissue samples were examined in a native state (35°C) and after exposure to different temperatures (45°C to 80°C). Results Rising temperature was accompanied by a decrease in the absorption coefficient and anisotropy factor and an increase in the scattering coefficient. These changes were only significant in the temperature range of 50° to 65°C (P

Summary A new scattering applicator for use in laser-induced thermotherapy (LITT) is presented. The applicator is mounted in front of a 400 μm quartz fiber and consists of a temperature stable plastic material with deposited scattering particles. The applicator provides a homogeneous axial scattering profile over an active length of 30 mm. The maximum power settings in porcine liver (in vitro) using a Nd:YAG-Laser and a cooled protective catheter were 31 W over an exposure period of 10 minutes. The resulting thermal lesions showed axial extensions of up to 50 mm and diameters of up to 33 mm, representing a total volume of 28.6 cm 3 .

Summary A dosimetry model was developed for the thermal laser treatment of biological tissue and applied to laser-induced thermotherapy of organ tumors. This model combines a Monte Carlo simulation for calculating photon distribution in the target volume, a finite difference method for computing heat dissipation and the Arrhenius formalism for predicting protein denaturation and subsequent tissue damage. Implementation was carried out on a Windows-based platform and enabled the three-dimensional control of the target volume. An in vitro evaluation in porcine liver revealed a difference of less than 7% with regard to the ablation volume.

Summary Introduction: For prediction of the effectiveness of laser-induced thermotherapy (LITT) of liver metastases and for the Planning of laser treatment it is indispensable to achieve knowledge about the intrahepatic light and temperature distribution in order to obtain data for an optimally adapted dosimetry. Material and methods: We evaluated the optical properties of normal and tumorous rabbit-liver ex-vivo using a double integrating sphere technique as well as a Monte-Carlo-simulation. These data were correlated with the measurement of the intrahepatic temperature ditrsibution in-vivo during LITT. Results: In our study we were able to show a positive correlation between ex-vivo results of optical properties and in-vivo results in temperature distribution. The absorption coefficient and scattering coefficients were significantly smaller in tumor tissue than in normal liver. This resulted in a higher optical penetration depth of the laser light into the tumor tissue (p Conclusions: These results provide a better understanding of laser-tissue interaction and may be helpful to investigators in the field of light dosimetry in liver tissue.

To evaluate gadolinium (Gd)-diethylenetriamine-pentaacetic-acid (DTPA)-enhanced magnetic resonance imaging (MRI) for follow-up monitoring of laser-induced thermotherapy (LITT) and to determine a useful examination schedule.LITT of the liver was performed in 55 rabbits using a neodymium: yttrium-aluminum-garnet (Nd:YAG) laser (4-W power output, 840-s exposure time). Gd-DTPA MRI and histologic examinations were performed at different times (0-168 days).Laser-induced lesions underwent regeneration and volume size reduction (69% after 168 days). The correlation coefficient (MR vs. macroscopic analysis) for the mean lesion diameter was r = 0.96. Histology of lesions comprised the four zones that correlated best with MRI findings. Coagulation necroses immediately after LITT was seen as an area of no enhancement on Gd-DTPA MRI. Circular enhancement was first seen 72-96 h after LITT, which was due to early mesenchymal proliferation.Gd-DTPA MRI is a good monitoring procedure for LITT. MRI should be performed 24 and 96 h after LITT.

Laser-induced thermotherapy is an in situ ablation method for the local treatment of liver tumors. The basic prerequisite for induction of adequate treatment volumes for clinical use was the development of a thermostable application system. In an ex vivo test series, the specially developed application system (diffuser tip) with 5760 J had a higher thermic loading capacity than the Ringmode applicator with 4200 J, thus enabling the induction of significantly larger lesions with a volume of 7.6 cm3. The results of a further in vivo test series demonstrated that the lesions were subject to a four-phase connective-tissue organization within a 6-month period. Furthermore, the same laser energy (4200 J) was associated with a significantly lower lesion volume of 2.5 cm3 in the in vivo than in the ex vivo test series. The influence of liver perfusion on the inducible lesion volume was examined in a further animal experimental study. By temporarily interrupting hepatic blood perfusion (Pringle's maneuver) during laser application, the effective volume could be increased to 50.3 cm3 (P < 0.01) using an optical beam splitter. These results show that the technical prerequisites for reliable clinical application of laser-induced thermotherapy have been fulfilled.

Background and Objective: Knowledge about optical parameters and the resultant light distribution in laser-treated tissue is important for predicting the effects of laser-induced thermotherapy of liver metastases (LITT). Materials and Methods: The absorption and scattering coefficients as well as the anisotropy factors and the optical penetration depths of human liver tissue and colorectal liver metastases were determined at 850, 980, and 1,064 nm under native and thermocoagulated conditions. Results: Liver metastases had a lower anisotropy factor, absorption, and scattering coefficient than healthy liver (P < 0.01), resulting in a significantly higher optical penetration depth in metastatic tissue. Coagulation significantly changes the optical parameters by reducing the optical penetration depth in both tissue types (P < 0.01). Conclusions: A greater optical penetration depth in metastatic tissue is advantageous for LITT, since larger tumor volumes can be coagulated. At the same time, an adjustment of the application parameters during LITT is necessary to achieve optimal therapeutic success. Lasers Surg. Med. 23:194‐203, 1998. © 1998 Wiley-Liss, Inc.

PURPOSE To optimize the MR sequences parameter for monitoring hyperthermic effects in the tissue during laser induced thermotherapy (LITT). MATERIAL AND METHODS Experimental studies were performed for the evaluation of MR-thermometry using a contrast-agent-water solution and a pig-liver. A T1-weighted TurboFLASH sequence and a FLASH-2D sequence were used. The TurboFLASH sequence was used with various T1 settings (between 100 and 1250 ms). MR findings were correlated with temperature measurements using a fluoride optical temperature measuring system in a distance of 1, 2, and 5 cm from the laser applicator. RESULTS Using the contrast-agent-water solution demonstrated the temperature sensitivity of both sequences. In vitro evaluations using pig liver demonstrated a near linear increase of signal versus increasing tissue temperatures in a distance of 1 cm to the tip of the laser applicator. Optimal visualization of the temperature effects was obtained using a T1 between 100 ms and 400 ms. Using the FLASH-2D sequence a signal loss was documented at a TR of 110 ms. CONCLUSION MR-thermometry using sequentially TurboFLASH and FLASH-2D sequences allowed a non-invasive monitoring of the laser induced temperature changes.

Background and Objective : This study investigated the feasibility of 850 nm diode laser-induced thermotherapy (LITT), a new procedure providing local hyperthermia and photocoagulation, a minimally invasive treatment of tumors, and other disorders such as benign prostate hyperplasia. Study Design/Material and Methods : An improved fiber optic diffuser inserted through a catheter was used to irradiate prostate, liver, and kidney tissue in-vitro. Experimental results were compared with predictions from mathematical simulations based on measured optical tissue parameters. Results : After 10 minutes of irradiation with 2-4.6 W CW laser power, sizable coagulation diameters had been achieved. In prostate and kidney tissue, temperature rises and coagulation diameters after laser irradiation were found to be smaller than in liver tissue. Those tissues also had a higher threshold for carbonization, thus reducing the risk of damage to the delivery system. Conclusion : The data suggest that a low power diode laser can be recommended for use in LITT to treat prostate and kidney tissue.

Purpose To analyse the value of MR-guided laser-induced thermotherapy (LITT) for palliative treatment of recurrent tumours of the head and neck region. Material and methods 8 patients with recurrent tumours of the head and neck region (squamous cell carcinomas n = 6, pleomorphic adenomas n = 2) underwent MR-controlled LITT. A 7 French laser applicator was inserted under local anaesthesia into the centre of the recurrent tumour. A Nd:YAG laser with a wavelength of 1064 nm was used. Therapy was monitored on-line using special MR thermosequences. Results Preinterventional contrast-enhanced MRI revealed a recurrent tumour of the head and neck region for all eight patients. All patients tolerated the procedures well under local anaesthesia, with no clinically relevant side effects. The MR thermosequences depicted up to 15 mm diameter areas of less signal near the laser tip. Postinterventional contrast-enhanced MRI revealed hypovascularized areas due to the resulting coagulative necrosis. Coagulative necrosis of 4 cc to 28 cc occurred in all patients, and a reduction of clinical symptoms was achieved in five. Conclusion The results obtained indicate that minimal invasive LITT can be a therapeutic alternative for palliative treatment of head and neck tumours.

PURPOSE: To evaluate magnetic resonance (MR) imaging-controlled laser-induced thermotherapy (LITT) in the treatment of recurrent head and neck tumors. MATERIALS AND METHODS: Six patients with recurrent nasopharyngeal tumors (squamous cell carcinoma [n = 4], pleomorphic adenoma [n = 2]) underwent LITT with local anesthesia. A 7-F introducing sheath was inserted into the center of the tumor followed by a specially designed laser emitter. Therapy was monitored on-line with MR thermometry, and the amount of necrosis was estimated with dynamic and static contrast material-enhanced sequences. RESULTS: All procedures were well tolerated with use of local anesthesia, with no clinically relevant side effects. MR thermometry depicted up to 15-mm-diameter areas of less signal intensity near the laser tip. Coagulative necrosis was achieved in all patients (volume range, 4-28 cm3), and clinical symptoms were reduced in four. CONCLUSION: MR imaging-controlled LITT may be a safe, minimally invasive alternative in the tr...

Background and Objectives Laser-induced thermotherapy (LITT) is a promising method for local treatment of liver metastases. The aim of this study was to compare the effect of LITT on lesion size when combined with hepatic arterial microembolization or complete hepatic blood flow occlusion. Study Design/Materials and Methods In a porcine liver model, LITT (30 W 15 minutes) was performed with either normal (n = 12), partially interrupted (arterial microembolization via a hepatic artery catheter n = 12) or completely interrupted hepatic perfusion (Pringle's maneuver, n = 12). LITT lesions were macro- and microscopically assessed after liver dissection. Results Hepatic inflow occlusion led to a fourfold increase in lesion volume after arterial microembolization and a ninefold increase after complete interruption (6.3. cm3 vs. 27.1 cm3 vs. 58.8 cm3, P

The aim of this study was to evaluate the feasibility of MR-guided laser-induced thermotherapy (LITT) for treatment of recurrent extrahepatic abdominal tumors. In 11 patients (6 women and 5 men; mean age 53 years, age range 29-67 years) with 14 lesions the following tumors were treated in this study: paravertebral recurrence of hypernephroma (n=1); recurrence of uterus carcinoma (n=1); recurrence of chondrosarcoma of the pubic bone (n=1); presacral recurrence of rectal carcinoma (n=1); recurrent anal cancer (n=1); metastases in the abdominal wall (n=1); and lymph node metastases from colorectal cancer (n=8). A total of 27 laser applications were performed. A fast low-angle shot 2D sequence (TR/TE/flip angle=102 ms/8 ms/70 degrees ) was used for nearly real-time monitoring during treatment. All patients had no other treatment option. Seventeen LITT sessions were performed using a conventional laser system with a mean laser power of 5.2 W (range 4.5-5.7 W), and 10 LITT session were performed using a power laser system with a mean laser power of 28.0 W. In 10 lesions total destruction could be achieved. In the remaining recurrent tumors, significant reduction of tumor volume by 60-80% was obtained. All patients tolerated the procedure well under local anesthesia. No complications occurred during treatment. Laser-induced thermotherapy is a practicable, minimally invasive, well-tolerated technique that can produce large areas of necrosis within recurrent tumors, substantially reducing active tumor volume if not resulting in outright destruction of tumor.

Laser-induced thermotherapy (LITT) is a so called in-situ- ablation technique which is used for the treatment of liver tumors. Coagulation necrosis is induced by transmitting the laser irradiation via quartz fibers directly into the tumor tissue. LITT represents similarly to surgical liver resection a local treatment form for liver metastases. The Nd-YAG laser (1064 nm) was used. The application system was placed percutaneously under open MRI control. On-line monitoring was done with MRI for evaluation of the postoperative follow-up we performed MRI-controls every 3 months. A total of 20 patients were treated. Due to the irradiation plan performed preoperatively, the treated tumors could be completely ablated by hyperthermia in all procedures. Complications were pleural effusion in 7 patients and a bile fistula and subcapsulary liver hematoma in one patient each. Local control of tumor growth can be achieved in tumors having undergone complete hyperthermic ablation. An assessment of the method regarding a prognostic benefit is not yet possible due to the short follow-up period and the small patient population.

Purpose: The aim of this study was to determine the energy (J/mm 3 tumor volume) and temperature required for a complete in-situ-ablation of experimental liver tumors. Methods: LITT was performed in VX-2 tumor-bearing rabbits using Nd-YAG-Laser (1064 nm) with a diffuser-tip applicator and a temperature feedback-system. The animals were randomized into 4 groups (n equals 20) that differed in the target temperature at the tumor border [45 degrees Celsius, 50 degrees Celsius, 55 degrees Celsius and 60 degrees Celsius]. Histological examination was done at 0 h, 24 h, 96 h and 14 days after LITT. Results: The pretreatment tumor volume of 2191 +/- 61 mm 3 was the same for all groups (p > 0.05). Energy and temperature required and the rate of incomplete tumor-ablation (recurrences) are listed below (* equals p 3 tumor volume. (2) A minimum temperature of 60 degrees Celsius on the tumor border presumed an application of 10 minutes.

An experimental setup will be presented which provides the detection of photon density waves (PDW) in transmission through tissue samples of up to 4 cm thickness. A laser diode (825 nm) which was modulated at frequencies between 40 - 1000 MHz served as light source. Amplitude and phase of the PDW were measured at various positions on tissue phantoms as well as during interstitial laser coagulation of tissue samples (porcine liver) by scanning source and detector. A Nd:YAG laser was used in combination with a scattering applicator to produce thermal lesions. Due to a change of the optical properties the actual size of the coagulated volume could be monitored during the therapy. Several phantom and in vitro experiments have been performed to show that this monitoring technique is capable of visualizing the coagulated region with a clinically relevant precision.

For prediction of the effectiveness of laser-induced thermotherapy (LITT) of liver metastases and for the planning of laser treatment it is indispensable to achieve knowledge about the intrahepatic light and temperature distribution in order to obtain data for an optimally adapted dosimetry. We evaluated the optical properties of normal and tumorous rabbit-liver ex-vivo using a double integrating sphere technique as well as a Monte-Carlo- simulation. These data were correlated with the measurement of the intrahepatic temperature distribution in-vivo during LITT. In our study we were able to show a positive correlation between ex-vivo results of optical properties and in-vivo results in temperature distribution. The absorption coefficient and scattering coefficients were significantly smaller in tumor tissue than in normal liver. This resulted in a higher optical penetration depth of the laser light into the tumor tissue (p < 0.01). Temperature measurement near the applicator was lower in tumor tissue, than that distant from the applicator (p < 0.01) corresponding to a higher temperature penetration depth. Both, higher optical and thermal penetration depth in the tumorous tissue was correlated with a significant increase in coagulation volume after LITT.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Purpose: To evaluate gadolinium-DTPA-enhanced MRI for follow-up monitoring of laser-induced thermotherapy (LITT) and to determine of a useful examination schedule. Materials and Methods: LITT Of the liver was performed in 55 rabbits using a Nd:YAG laser (4 w power output, 840 s exposure time). Gd-DTPA MRI and histological examinations were performed at different times (0 - 168 days). Results: Laser- induced lesions underwent regeneration and volume size reduction (69% after 168 days). The correlation coefficient (MR vs macroscopic analysis) for the mean lesion diameter was r equals 0.96. Histology of lesions comprised the four zones that correlated best with MRI findings. Coagulation necroses immediately after LITT were seen as an area of no enhancement on Gd-DTPA MRI. Circular enhancement was first seen 72 - 96 hours after LITT, which was due to early mesenchymal proliferation. Conclusions: Gd-DTPA MRI is a good monitoring procedure for LITT. MRI should be performed 24 and 96 hours after LITT.

The purpose of the study was to evaluate Gd-DTPA-enhanced MRI for the follow-up of laser-induced thermotherapy (LITT) in the treatment of liver metastases. Interstitial laser-induced thermotherapy (LITT) was performed in 55 chinchilla bastard rabbits with a Nd:YAG laser and a specially developed diffuser tip applicator. The animals were examined at different times using MRI and histological methods. T1-weighted spin-echo sequences were made with gadolinium-DTPA and submitted to correlation analysis. The analysis yielded a good correlation (r equals 0.96) between the largest lesion diameters. Lesions showed discontinuous regeneration kinetics with a 41% volume reduction 1 month after LITT. MRI of the lesion directly after LITT showed a hyperintense transition zone. Following the application of intravenous contrast medium, transition zone enhancement was first seen 72 - 96 hours after LITT. Even after 6 months, the laser-induced lesion is visualized as a non-enhanced area. Lesion regeneration followed the principles of wound healing. It is concluded that gadolinium-DTPA- enhanced MRI yielded definitive criteria for the follow-up assessment of LITT.

The aim of the present animal experimental study was to investigate the effect of temporarily interrupting hepatic perfusion as well as the application mode on inducible coagulation volumes. Experiments were carried out using a Nd:YAG-laser at a wavelength of 1064 nm. A special multifiber optical component was used. Ten German hybrid pigs served as the experimental animals. All animals were sacrificed four hours after the end of application, and the livers were removed for histological examination. With a single application, a mean lesion volume of 2503 mm 3 resulted from a total applied energy of 4356 J. Under temporary occlusion of hepatic circulation a lesion volume of 7452 mm 3 was found (p less than 0.01). Multifiber laser application with hepatic circulation led to a mean volume of 14612 mm 3 . During interrupted circulation, overlapping tissue lesions with a mean volume of 50285 mm 3 were induced (p less than 0.01). Microscopic examination showed that the rim seen macroscopically was identical. As well the application mode as the hepatic circulation are statistically significant parameters for the inducible lesion volumes. The interruption of the liver perfusion during laser application led to a significant increase of the hyperthermically induced tissue lesion for single- and multifiber applications.

As a high number of metastases grow in the liver, new treatment methods have been developed. Laser-induced thermotherapy (LITT) has recently applied for a minimally invasive technique in local treatment of liver metastases. Laser light was performed using Neodymium yttrium aluminum garnet (Nd-YAG, wavelength 1064 nm) delivered through a quartz fiber optic with a diameter of 400 micrometer with diffuse light emission. Laser light is converted into heat in the target area with an ensuing coagulative necrosis, secondary degeneration and atrophy, tumor shrinkage with minimal damage to surrounding structures. The size of heated volume depends on laser power, laser irradiation time, the way it reaches the target area and optical and thermal characteristics of the treated tissue. Pilot clinical studies have demonstrated that this technique is practical for the palliation of hepatic tumors. The clinical success of the thermotherapy depends on the optimal localization of the laser applicator in the center of the lesion, an optimal 'online monitoring' of thermal changes in the treated tissue and an exact documentation of the therapy effect and the local tumor controlrate. The individual optimization of two special developed thermosensitive sequences allows an exact monitoring of the progress of LITT to the treated lesion and surrounding structures. The purpose of this paper is to describe our experimental and clinical experience with MR-guided LITT for treatment of liver metastases and follow-up evaluation in larger series.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A computer model will be presented which enables the calculation of interstitial temperature distributions during laserinduced thermotherapy. Prerequisite for the simulation is the knowledge of the individual optical and thermal tissue properties. To reach an acceptable duration for the simulation of long laser treatments a simplified spherical geometry was chosen since it fits best to the radiation field of diffusing applicators. Comparison of the calculated temperature behavior with experimental data shows good agreement. A new applicator design with internal cooling will be presented, which enables the coagulation of larger volumes at lower contact temperatures.

Laser induced thermotherapy is a new procedure for local hyperthermia and photocoagulation allowing minimal invasive treatment of tumors and other disorders such as benign prostatic hypertrophia.

Laser-induced thermotherapy (LITT) or interstitial laser thermotherapy is an in situ ablation technique for the treatment of malignant tumors of the liver. 1,2 The potential of LITT is that laser light is directly transmitted through flexible bare fibers into the tumor tissue with high precision. The biologic effect of the laser light is based on the transformation of laser photon energy into heat by the absorption of tissue-specific chromophores. The aim is to induce uniform coagulation necrosis of the treatment volume. 3 Of great importance to the method’s success is the size of the induced coagulation necrosis, which must contain the whole volume of the tumor tissue. This lesion size largely depends on the temperature distribution in the target volume, which is determined partly by the blood perfusion in the target organ. 4,5 In organs with a high blood perfusion, such as the liver, a cooling effect results because of the temperature difference between the hyperthermic area and blood. 6,7 Temporary interruption of hepatic blood flow by occlusion of hepatic inflow vessels (Pringle maneuver) during LITT has been proven to increase its efficacy. 8–11 The Pringle maneuver usually requires laparotomy 10,11 or at least laparoscopy 12 and may therefore be difficult to repeat in cases of insufficient therapy. LITT, however, can be applied percutaneously without laparotomy or laparoscopy and can thus be easily repeated. 1,2 An alternative to the temporary interruption of hepatic arterial blood flow to liver tumors is the application of degradable starch microspheres (DSM), as used for chemoembolization. 13,14 The purpose of this study was to assess the effect of combined LITT and DSM on intrahepatic temperature distribution and tumor response in rats with liver tumors.

procedure. LITT was done after agreement from the local ethics committee and with the patients’ informed consent. All patients tolerated the procedure well; six had mild nausea and a symptomless right subphrenic haemorrhage developed in one. No deaths, infections, or liver or bile-duct injury occurred. During follow-up, 23 of 99 treated patients died: one of myocardial infarction, one from a stroke, 13 from tumour progression in the liver, and eight from tumour progression in other locations. The cumulative survival rate was 0·88 after 12 months, 0·70 after 24 months, and 0·42 after 36 months. Median survival time, calculated by the Kaplan-Meier method, was 36·4 months (figure). In patients with liver metastases of colorectal cancer, local tumour destruction with LITT under local anaesthesia is well tolerated and results in improved clinical outcome and survival. Our data can be a basis for a randomised comparison of LITT versus surgery.