Interstitial laser hyperthermia: a new approach for treating liver metastases

Temperature-controlled laser thermal therapy system using a newly developed laparoscopic system equipped with an ultra-compact thermographic camera

Laser thermal therapy is one of the treatments for malignant tumors. We developed a thermal endoscope using an ultra-compact thermo-sensor and established a new laparoscopic laser thermal therapy system to heat cancer tissue at an appropriate temperature, focusing on the fact that thermographic cameras are capable of two-dimensional temperature mapping. Hepatocellular carcinoma (N1S1) cells were implanted into the livers of Sprague-Dawley rats (n = 13) to create orthotopic hepatocellular carcinoma. Six of the rats underwent laparoscopic laser thermotherapy (70 °C, 5 min) using the newly developed system, and the others underwent laparoscopic insertion only. Lesion volume measurement and histological evaluation were performed in all of the rats. The laparoscopic laser thermal therapy system provided stable temperature control. When a temperature of 70 °C was used for the set temperature, the temperature of the target cancer was maintained within the range of 68-72 °C for 93.2% of the irradiation time (5 min). The median volume of the tumors that were thermally treated was significantly smaller than that of the untreated tumors. The newly developed laparoscopic laser thermal therapy system was capable of maintaining the temperature of the tumor surface at any desired temperature and was proven to be effective in treatment of the rat hepatocellular carcinoma model.

Nanoparticle-Mediated Photothermal Therapy Limitation in Clinical Applications Regarding Pain Management

The development of new effective cancer treatment methods has attracted much attention, mainly due to the limited efficacy and considerable side effects of currently used cancer treatment methods such as radiation therapy and chemotherapy. Photothermal therapy based on the use of plasmonically resonant metallic nanoparticles has emerged as a promising technique to eradicate cancer cells selectively. In this method, plasmonic nanoparticles are first preferentially uptaken by a tumor and then selectively heated by exposure to laser radiation with a specific plasmonic resonant wavelength, to destroy the tumor whilst minimizing damage to adjacent normal tissue. However, several parameters can limit the effectiveness of photothermal therapy, resulting in insufficient heating and potentially leading to cancer recurrence. One of these parameters is the patient's pain sensation during the treatment, if this is performed without use of anesthetic. Pain can restrict the level of applicable laser radiation, cause an interruption to the treatment course and, as such, affect its efficacy, as well as leading to a negative patient experience and consequential general population hesitancy to this type of therapy. Since having a comfortable and painless procedure is one of the important treatment goals in the clinic, along with its high effectiveness, and due to the relatively low number of studies devoted to this specific topic, we have compiled this review. Moreover, non-invasive and painless methods for temperature measurement during photothermal therapy (PTT), such as Raman spectroscopy and nanothermometry, will be discussed in the following. Here, we firstly outline the physical phenomena underlying the photothermal therapy, and then discuss studies devoted to photothermal cancer treatment concerning pain management and pathways for improved efficiency of photothermal therapy whilst minimizing pain experienced by the patient.

Targeted Photothermal Therapy of Melanoma in C57BL/6 Mice using Fe3O4@Au Core-shell Nanoparticles and Near-infrared Laser

BACKGROUND

Gold nanoshells can be tuned to absorb a particular wavelength of light. As a result, these tunable nanoparticles (NPs) can efficiently absorb light and convert it to heat. This phenomenon can be used for cancer treatment known as photothermal therapy. In this study, we synthesized Fe₃O₄@Au core-shell NPs, magnetically targeted them towards tumor, and used them for photothermal therapy of cancer.

OBJECTIVE

The main purpose of this research was to synthesize Fe₃O₄@Au core-shell NPs, magnetically target them towards tumor, and use them for photothermal therapy of cancer.

MATERIAL AND METHODS

In this experimental study, twenty mice received 2 × 10⁶ B16-F10 melanoma cells subcutaneously. After tumors volume reached 100 mm³, the mice were divided into five groups including a control group, NPs group, laser irradiation group, NPs + laser group and NPs + magnet + laser group. NPs were injected intravenously. After 6 hours, the tumor region was irradiated by laser (808 nm, 2.5 W/cm², 6 minutes). The tumor volumes were measured every other day.

RESULTS

The effective diameter of Fe₃O₄@Au NPs was approximately 37.8 nm. The average tumor volume in control group, NPs group, laser irradiation group, NPs + laser irradiation group and NPs + magnet + laser irradiation group increased to 47.3, 45.3, 32.8, 19.9 and 7.7 times, respectively in 2 weeks. No obvious change in the average body weight for different groups occurred.

CONCLUSION

Results demonstrated that magnetically targeted nano-photothermal therapy of cancer described in this paper holds great promise for the selective destruction of tumors.

Magnetic Resonance Imaging-Guided Laser Interstitial Thermal Therapy for Epilepsy: Systematic Review of Technique, Indications, and Outcomes

BACKGROUND

For patients with focal drug-resistant epilepsy (DRE), surgical resection of the epileptogenic zone (EZ) may offer seizure freedom and benefits for quality of life. Yet, concerns remain regarding invasiveness, morbidity, and neurocognitive side effects. Magnetic resonance-guided laser interstitial thermal therapy (MRgLITT) has emerged as a less invasive option for stereotactic ablation rather than resection of the EZ.

OBJECTIVE

To provide an introduction to MRgLITT for epilepsy, including historical development, surgical technique, and role in therapy.

METHODS

The development of MRgLITT is briefly recounted. A systematic review identified reported techniques and indication-specific outcomes of MRgLITT for DRE in human studies regardless of sample size or follow-up duration. Potential advantages and disadvantages compared to available alternatives for each indication are assessed in an unstructured review.

RESULTS

Techniques and outcomes are reported for mesial temporal lobe epilepsy, hypothalamic hamartoma, focal cortical dysplasia, nonlesional epilepsy, tuberous sclerosis, periventricular nodular heterotopia, cerebral cavernous malformations, poststroke epilepsy, temporal encephalocele, and corpus callosotomy.

CONCLUSION

MRgLITT offers access to foci virtually anywhere in the brain with minimal disruption of the overlying cortex and white matter, promising fewer neurological side effects and less surgical morbidity and pain. Compared to other ablative techniques, MRgLITT offers immediate, discrete lesions with real-time monitoring of temperature beyond the fiber tip for damage estimates and off-target injury prevention. Applications of MRgLITT for epilepsy are growing rapidly and, although more evidence of safety and efficacy is needed, there are potential advantages for some patients.

Delirium and topographical disorientation associated with glioblastoma multiforme tumour progression into the isthmus of the cingulate gyrus

Since there is no cure for glioblastoma multiforme (GBM), the goal of treatment becomes prolonging the survival through cytoreduction while minimising neurological deficits. In this case report, laser interstitial thermal therapy (LITT) was used once the tumour progressed into the isthmus of the cingulate gyrus. One year after temporal lobectomy, disorders of memory, emotion, personality and navigation, likely related to limbic system involvement along with hallucinations and fluctuating cognition occurred as the tumour progressed. After ablation of the posterior cingulum, worsening of topographical disorientation was observed.Per literature review, delirium has been noted in patients with strokes involving the right-sided temporo-parieto-occipital junction, and topographical disorientation has been associated with lesions of the right posterior cingulum. Alternative causes of these deficits were ruled out, leaving structural changes as the primary explanation. This is the first report of the neurological deficits associated with tumour progression and vasogenic oedema in this region.

Computational analysis of linear energy modulation for laser thermal coagulation

Accurate treatment planning and monitoring are critical factors to ensure safe and effective outcomes of laser thermal coagulation (LTC). Computational and experimental models based upon linear energy modulation were deployed to predict temperature distribution and thermal damage within ex vivo porcine liver. 1470-nm Gaussian emission was confirmed by using digital imaging and the customized goniometry. The tissue temperature was maintained in the pre-determined range (65~75 °C) to induce thermally destructive volumes of 0.23 cm³ (simulation) and 0.17 ± 0.05 cm³ (experiment) once the applied power was linearly reduced from 3.5 W to 0.2 W in 50 s ("3.5 W fast slope" laser modulation mode). The proposed model may be a useful tool to predict thermal responses of the tissue during LTC.

Temperature-monitored optical treatment for radial tissue expansion

Esophageal stricture occurs in 7-23% of patients with gastroesophageal reflux disease. However, the current treatments including stent therapy, balloon dilation, and bougienage involve limitations such as stent migration, formation of the new strictures, and snowplow effect. The purpose of the current study was to investigate the feasibility of structural expansion in tubular tissue ex vivo during temperature-monitored photothermal treatment with a diffusing applicator for esophageal stricture. Porcine liver was used as an ex vivo tissue sample for the current study. A glass tube was used to maintain a constant distance between the diffuser and tissue surface and to evaluate any variations in the luminal area after 10-W 1470-nm laser irradiation for potential stricture treatment. The 3D goniometer measurements confirmed roughly isotropic distribution with less than 10% deviation from the average angular intensity over 2π (i.e., 0.86 ± 0.09 in arbitrary unit) from the diffusing applicator. The 30-s irradiation increased the tissue temperature up to 72.5 °C, but due to temperature feedback, the interstitial tissue temperature became saturated at 70 °C (i.e., steady-state error = ±0.4 °C). The irradiation times longer than 5 s presented area expansion index of 1.00 ± 0.04, signifying that irreversible tissue denaturation permanently deformed the lumen in a circular shape and secured the equivalent luminal area to that of the glass tube. Application of a temperature feedback controller for photothermal treatment with the diffusing applicator can regulate the degree of thermal denaturation to feasibly treat esophageal stricture in a tubular tissue.

Stereotactic Laser Ablation for Medically Intractable Epilepsy: The Next Generation of Minimally Invasive Epilepsy Surgery

Epilepsy is a common, disabling illness that is refractory to medical treatment in approximately one-third of patients, particularly among those with mesial temporal lobe epilepsy. While standard open mesial temporal resection is effective, achieving seizure freedom in most patients, efforts to develop safer, minimally invasive techniques have been underway for over half a century. Stereotactic ablative techniques, in particular, radiofrequency (RF) ablation, were first developed in the 1960s, with refinements in the 1990s with the advent of modern computed tomography and magnetic resonance-based imaging. In the past 5 years, the most recent techniques have used MRI-guided laser interstitial thermotherapy (LITT), the development of which began in the 1980s, saw refinements in MRI thermal imaging through the 1990s, and was initially used primarily for the treatment of intracranial and extracranial tumors. The present review describes the original stereotactic ablation trials, followed by modern imaging-guided RF ablation series for mesial temporal lobe epilepsy. The developments of LITT and MRI thermometry are then discussed. Finally, the two currently available MRI-guided LITT systems are reviewed for their role in the treatment of mesial temporal lobe and other medically refractory epilepsies.

Radiofrequency ablation of hepatocellular carcinoma

Radiofrequency ablation (RFA), usually performed under percutaneous ultrasound guidance, is considered the gold standard among minimally invasive therapies. On the strength of some recent randomized trials, its indications include operable patients with small hepatocellular carcinoma and inoperable patients with more advanced disease also in combination with other therapies. RFA has lower complication rates and costs less than surgery.

Interstitial laser thermotherapy of a rat liver tumour: effect of hepatic inflow occlusion

BACKGROUND AND OBJECTIVE

Interstitial laser thermotherapy was used to treat rat liver tumours. The aim was to investigate the influence of temperature and temporary hepatic inflow occlusion on tumour growth and blood perfusion.

STUDY DESIGN/MATERIALS AND METHODS

Liver tumours were treated at 44°C at the tumour border for 30 minutes, hepatic inflow occlusion only, or a combination of these methods. Interstitial laser Doppler flowmetry was used to measure hepatic perfusion at the tumour border during and after heat treatment, for a total time of 60 minutes. Tumour growth was evaluated 6 days after treatment.

RESULTS

Tumours subjected to the combined treatment of hepatic inflow occlusion and interstitial laser thermotherapy displayed a blood perfusion reduction 30 minutes after treatment to 18 ± 5% of initial perfusion, which was significantly lower than achieved with thermotherapy alone (52 ± 10%, P = 0.02). The combined treatment and treatment with thermotherapy alone resulted in relative tumour growth of 0.3 ± 0.1 and 1.0 ± 0.2, respectively (P = 0.04).

CONCLUSION

Inflow occlusion enhanced the effect of thermotherapy not by augmenting treatment temperatures but by increasing the thermal sensitivity of the tumour, reflected by an immediate effect on tumour blood perfusion.

Activation of tumor-specific T lymphocytes after laser-induced thermotherapy in patients with colorectal liver metastases

PURPOSE

To asses if laser-induced thermotherapy (LITT) induces a specific cytotoxic T cell response in patients treated with LITT for colorectal cancer liver metastases.

METHODS

Eleven patients with liver metastases of colorectal cancer underwent LITT. Blood was sampled before and after LITT. Peripheral T cell activation was assessed by an interferon gamma (IFNg) secretion assay and flow cytometry. Test antigens were autologous liver and tumor lysate obtained from each patient by biopsy. T cells were stained for CD3/CD4/CD8 and IFNg to detect activated T cells. The ratio of IFNg positive to IFNg negative T cells was determined as the stimulation index (SI). To assess cytolytic activity, T cells were co-incubated with human colorectal cancer cells (CaCo) and cytosolic adenylate kinase release was measured by a luciferase assay.

RESULTS

IFNg secretion assay: before LITT SI was 12.73 (+/-4.83) for CD3+, 4.36 (+/-3.32) for CD4+ and 3.64 (+/-1.77) for CD8+ T cells against autologous tumor tissue. Four weeks after LITT SI had increased to 92.09 (+/-12.04) for CD3+ (P < 0.001), 42.92 (+/-16.68) for CD4+ (P < 0.001) and 47.54 (+/-15.68) for CD8+ T cells (P < 0.001) against autologous tumor tissue. No increased SI was observed with normal liver tissue at any time point. Cytotoxicity assay: before LITT activity against the respective cancer cells was low, with RLU = 1,493 (+/-1,954.68), whereas after LITT cytolytic activity had increased to RLU = 7,260 [+/-3,929.76 (P < 0.001)].

CONCLUSION

Patients with liver metastases of colorectal cancer show a tumor-specific cytotoxic T cell stimulation and a significantly increased cytolytic activity of CD3+, CD4+ and CD8+ T cells after LITT against an allogenic tumor (CaCo cell line).

Optimization and real-time control for laser treatment of heterogeneous soft tissues

Predicting the outcome of thermotherapies in cancer treatment requires an accurate characterization of the bioheat transfer processes in soft tissues. Due to the biological and structural complexity of tumor (soft tissue) composition and vasculature, it is often very difficult to obtain reliable tissue properties that is one of the key factors for the accurate treatment outcome prediction. Efficient algorithms employing in vivo thermal measurements to determine heterogeneous thermal tissues properties in conjunction with a detailed sensitivity analysis can produce essential information for model development and optimal control. The goals of this paper are to present a general formulation of the bioheat transfer equation for heterogeneous soft tissues, review models and algorithms developed for cell damage, heat shock proteins, and soft tissues with nanoparticle inclusion, and demonstrate an overall computational strategy for developing a laser treatment framework with the ability to perform real-time robust calibrations and optimal control. This computational strategy can be applied to other thermotherapies using the heat source such as radio frequency or high intensity focused ultrasound.

Nanoshell-mediated laser surgery simulation for prostate cancer treatment

Laser surgery, or laser-induced thermal therapy, is a minimally invasive alternative or adjuvant to surgical resection in treating tumors embedded in vital organs with poorly defined boundaries. Its use, however, is limited due to the lack of precise control of heating and slow rate of thermal diffusion in the tissue. Nanoparticles, such as nanoshells, can act as intense heat absorbers when they are injected into tumors. These nanoshells can enhance thermal energy deposition into target regions to improve the ability for destroying larger cancerous tissue volumes with lower thermal doses. The goal of this paper is to present an integrated computer model using a so-called nested-block optimization algorithm to simulate laser surgery and provide transient temperature field predictions. In particular, this algorithm aims to capture changes in optical and thermal properties due to nanoshell inclusion and tissue property variation during laser surgery. Numerical results show that this model is able to characterize variation of tissue properties for laser surgical procedures and predict transient temperature fields comparable to those measured by in vivo magnetic resonance temperature imaging techniques. Note that the computational approach presented in the study is quite general and can be applied to other types of nanoparticle inclusions.

Efficacy of direct electrical current therapy and laser-induced interstitial thermotherapy in local treatment of hepatic colorectal metastases: an experimental model in the rat

BACKGROUND

Local antitumoral therapy of metastases is an important tool in the palliative treatment of advanced colorectal cancer. Several authors have recently reported on successful local treatment of different malignant diseases with low-level direct current therapy. The aim of the present study was to compare the effectiveness of direct current therapy with the established laser-induced thermotherapy (LITT) on experimental colorectal liver metastases.

MATERIALS AND METHODS

Colorectal metastases were induced in 49 BD IX rats by injection of colon cancer cells beneath the liver capsule. Three weeks after induction, tumor volumes and sizes were estimated with magnetic resonance imaging and by manual measurement of the largest tumor diameter, and two treatment groups and two control groups were established. Direct current (80 C/cm(3)) versus LITT (2 W; 5 to 10 min) was locally applied via laparotomy. Control groups were sham treated. Tumor growth was analyzed 5 wk after therapy by manual measurement of the maximal diameter and histopathological examination was performed.

RESULTS

Measurement of tumor sizes 5 wk after therapy confirmed a significant antitumoral effect of direct current (1.6-fold tumor enlargement) and of LITT (1.3-fold tumor enlargement), compared with controls (2.8-fold and 2.9-fold tumor enlargement). However, after 5 wk, LITT was significantly more effective in limiting tumor growth than direct current treatment (P </= 0,001). Histopathological analysis revealed a complete response rate of 21% and a partial response rate of 77% in the electric current group. In comparison, LITT treated livers showed a complete response rate of 22% and a partial response rate of 78% (n.s.).

CONCLUSIONS

The data confirm that direct current therapy and LITT are effective treatment strategies in the palliative control of colorectal hepatic metastases, with both therapies being equally effective in inducing a complete or partial tumor necrosis.

Termoablação a laser de tumores hepáticos: atualização

A termoablação por raio laser de tumores hepáticos tem despontado como alternativa válida de tratamento em pacientes que não são candidatos a ressecção cirúrgica. O procedimento pode ser realizado por via percutânea, laparoscópica ou por laparotomia, e orientado por métodos de imagem. O objetivo deste trabalho é apresentar o mecanismo de ação deste método, bem como as suas indicações, contra-indicações, complicações e resultados clínicos, baseados em revisão bibliográfica.

Interstitial laser thermotherapy for liver tumours

BACKGROUND

Primary hepatocellular carcinoma (HCC) and metastases from colorectal cancer are the most common malignant liver tumours. Surgical resection is the optimum treatment in suitable patients. Interstitial laser thermotherapy (ILT) is gaining acceptance for the treatment of irresectable liver tumours and as a potential alternative to surgery. An understanding of the principles of therapy and review of clinical outcomes may allow better use of this technology.

METHOD

An electronic search using the Medline database was performed for studies on the treatment of hepatic malignancy published between January 1983 and February 2003.

RESULTS

Current information on the efficacy of ILT is based on prospective studies. ILT appears to be a safe and minimally invasive technique that consistently achieves tumour destruction. The extent of destruction depends on the fibre design, delivery system, tumour size and tumour biology. Real-time magnetic resonance imaging provides the most accurate assessment of laser-induced tumour necrosis. In selected patients with HCC and colorectal cancer liver metastases, ILT achieves complete tumour necrosis, provides long-term local control, and improves survival, compared with the natural history of the disease. In addition, ILT has survival benefits for patients with other tumour types, especially those with isolated liver metastases from a breast cancer primary.

CONCLUSION

ILT improves overall survival in specific patients with liver tumours. Advances in laser technology and refinements in technique, and a better understanding of the processes involved in laser-induced tissue injury, may allow ILT to replace surgery as the procedure of choice in selected patients with liver malignancies.

Thermal ablative therapy for malignant liver tumors: a critical appraisal

The management of primary and secondary malignant liver tumors poses a great challenge to clinicians. Although surgical resection is the gold-standard treatment, most patients have unresectable malignant liver tumors. Over the past decade, various modalities of loco-regional therapy have gained much interest. Among them, thermal ablative therapy, including cryotherapy, microwave coagulation, interstitial laser therapy, and radiofrequency ablation (RFA), have been proven to be safe and effective. Despite the effective tumor eradication achieved within cryotherapy, the underlying freeze/thaw mechanism has resulted in serious complications that include bleeding from liver cracking and the 'cryoshock' phenomenon. Thermal ablation using microwave and laser therapy for malignant liver tumors is curative and is associated with minimal complications. However, this treatment modality is effective only for tumors <3 cm diameter. Radiofrequency ablation seems to be the most promising form of thermal ablative therapy in terms of a lower complication rate and a larger volume of ablation. However, its use is restricted by the difficulty encountered when using imaging studies to monitor the areas of ablation during and after the procedure. Moreover, the techniques of RFA need to be refined in order to achieve the same oncological radicality of malignant liver tumors as achieved by surgical resection. As each of the loco-regional therapies has its own advantages and limitations, a multidisciplinary approach using a combination of therapies will be the future trend for the management of malignant liver tumors.

A critical review of the major indicators of prognosis after resection of hepatic metastases from colorectal carcinoma

Hepatic resections for metastatic colorectal cancer have dramatically increased, and there is clear evidence of the effectiveness of this type of surgery. Controversy, however, persists regarding appropriate patient selection, extent and timing of liver resection, and adjuvant or alternative therapeutic options. This article reviews the authors' experience with more than 600 hepatic resections and the relevant literature is discussed. The results underscore the importance of macroscopically and histologically complete tumor clearance, a so-called "R0 resection."

Magnetic resonance imaging-guided laser thermal ablation of renal tumours

OBJECTIVE

To test the hypothesis that magnetic resonance imaging (MRI)-guided laser thermal ablation (LTA) of inoperable renal tumours is a safe, tolerable and potentially effective treatment.

PATIENTS AND METHODS

Nine patients (aged 56-81 years) with malignant renal tumours underwent percutaneous LTA under MRI guidance in a 0.5 T open magnet. Real-time colour thermal mapping was used to monitor tumour ablation, and the follow-up was with gadolinium-enhanced MRI at 6 weeks and (where appropriate) 3-4 months after the procedure. Tumour volume and percentage tumour enhancement before and after ablation were compared. The percentage of tumour ablated on real-time T1-weighted thermal maps was compared with that on gadolinium-enhanced follow-up MRI.

RESULTS

The mean (range) follow-up was 16.9 (3-32) months after the first ablation. The mean tumour size did not change significantly, but the mean percentage of viable tumour decreased significantly from 73.7% before to 29.5% after ablation (P = 0.012, Wilcoxon signed-ranks test). Thermal maps correlated moderately well with follow-up MRI in predicting the extent of tumour ablation (Pearson correlation coefficient 0.55). There were two minor and one major complication.

CONCLUSION

In this pilot study of patients unsuitable for surgery, MRI-guided LTA of renal tumours was safe, feasible (being well tolerated by the patient) and significantly reduced enhancing tumour volume by a mean of 45%.

Ablative therapy for liver tumours

Established ablative therapies for the treatment of primary and secondary liver tumours, including percutaneous ethanol injection, cryotherapy, and radiofrequency ablation, are discussed. Newer techniques such as magnetic resonance imaging guided laser interstitial thermal therapy of liver tumours has produced a median survival rate of 40.8 months after treatment. The merits of this newly emerging technique are discussed, together with future developments, such as focused ultrasound therapy, which holds the promise of non-invasive thermoablation treatment on an outpatient basis.

Influence of the bridging effect by sequential laser application on tissue ablation in an ex vivo model, taking organ perfusion into account

OBJECTIVE

To improve the efficacy of interstitial laser coagulation of tissue by causing a 'bridging' effect, using a sequential multiple-probe procedure on an ex vivo kidney model, as only a limited area of tissue is destroyed with a single probe and the coagulation takes longer when multiple punctures are used.

MATERIALS AND METHODS

A laser beam was generated using a Nd:YAG laser and applied to kidney tissue by a diffuser tip (quartz glass cap 2 x 19 mm). For sequential laser application (SLA), three probes were placed through punctures into kidney tissue, at 5 or 10 mm apart. The laser energy was applied in different time-energy combinations through the three probes. The effect of SLA was compared with that from one probe delivering the optimal PowerMode 180 protocol (Dornier, Germering, Germany), which represents the standard energy protocol for the clinical treatment of parenchymal organs using this laser device. An isolated porcine kidney was chosen for laser coagulation under different conditions of perfusion. The ablative efficacy was defined as the volume of necrosis per minute.

RESULTS

Applying various time-energy combinations to isolated unperfused porcine kidney caused extensive tissue ablation (5.6 mL). In trials with saline and blood perfusion for improved cooling, the necrotic volume was 2.5 and 3.9 mL, respectively (with no carbonization, 3.2 mL). Compared with a single-probe procedure, the ablation efficacy was 10 times better with SLA coagulation. This improvement was initiated by the bridging effect: coagulation in neighbouring areas affects perfusion and convection to an extent that induces the formation of bridges of necrosis between the probes.

CONCLUSION

Tissue ablation is markedly improved by interstitial laser coagulation using a sequential multiple-probe technique.

Durability of laser probes in interstitial thermotherapy: investigations on an ex vivo model of effect of carbonization

BACKGROUND AND PURPOSE

Interstitial laser application is successful for clinical tissue ablation in various organs. One great drawback of this method is the high costs caused by the vulnerability of the probes. Our objective was to investigate whether the prevention of carbonization deposits on laser probes averts reduced transmission after the application of high laser energy.

MATERIALS AND METHODS

Interstitial laser probes were used to pierce an in vitro kidney model, and 9900 J of energy (Nd:YAG laser) was applied. The transmission of the laser probe was determined and compared with that of a reference probe.

RESULTS

The application of laser energy, up to a total of 49,500 J, did not reduce transmission. The deviation of the transmission comparing working probes and the reference probe was between 2% and 7%. The application of high energy (40 W) over a longer period (>20 seconds) led to carbonization and consequent distinct reduction of transmission.

CONCLUSIONS

The durability of laser probes can be prolonged by preventing carbonization. The economic effect achieved is the repeated use of the probes at less expense.

Status of hyperthermia in the treatment of advanced liver cancer

The vast majority of patients with malignant liver tumors have inoperable disease. These patients must rely on chemotherapy, radiotherapy, and various locoregional treatments. Although these treatments have demonstrated encouraging response rates, symptom palliation and occasional down staging of tumors, their impact on survival is minor. As a result there has been renewed interest in hyperthermia as a treatment option. This study reviews the current modalities of hyperthermia in terms of clinical results, side effects, limitations, and therapeutic standing.

Histopathological correlation to MRI findings during and after laser-induced thermotherapy in a pig pancreas model

RATIONALE AND OBJECTIVES

To investigate whether percutaneous laser-induced thermotherapy (LITT) with continuous magnetic resonance (MR) monitoring of thermal effects within the pancreas is feasible in a porcine model.

METHODS

Laser applicators were placed in the pancreas of 15 female pigs. A temperature-sensitive (thermo--fast low-angle shot) sequence was used for continuous monitoring of thermal effects during LITT at 1.5 T. Follow-up MR images were acquired, the pigs were observed for 7 days, and then a pathological examination was performed after sacrifice.

RESULTS

Continuous MR monitoring visualized thermal effects in pancreatic tissue and thermal damage of the spleen (n = 1), the left kidney (n = 1), and peripancreatic fat (n = 4) but missed the thermal damage of the duodenum (n = 2). Thermal-induced lesions (10--32-mm diameter) were clearly visualized on contrast-enhanced T1-weighted images.

CONCLUSIONS

Laser-induced thermotherapy of pancreatic tissue was feasible in this porcine model, and online monitoring was practicable. Further studies are necessary to increase the accuracy of online MR imaging of thermal effects.

Treatment of hepatocellular carcinoma by percutaneous laser hyperthermia

BACKGROUND AND AIM

The majority of patients with hepatocellular carcinoma (HCC) are unsuitable for partial liver resection or transplantation because of unfavorable tumor characteristics or underlying severe liver disease. Techniques of in situ tumor ablation may be an alternative to resection and have the advantage of reduced morbidity and mortality. Percutaneous laser-induced hyperthermia produces predictable areas of tumor necrosis with minimal complications. This study assesses the effectiveness of percutaneous interstitial laser hyperthermia in eight patients with hepatocellular carcinoma occurring on a background of chronic liver disease.

METHODS

Patients with confirmed HCC with less than five tumor nodules of less than 7 cm maximum diameter were selected for treatment. Tumor response was monitored by dynamic CT, alpha-fetoprotein levels and liver function tests. Patients were discharged within 24 h.

RESULTS

There were six males and two females, with liver disease of Child-Pugh grade C in five, and grade B in the others. Two patients had tumor recurrence following previous segmental resection. Four had solitary lesions, and individual lesion size ranged between 3 and 7 cm. Avascularity and significant necrosis of the tumor was achieved on all lesions less than 4 cm, but was unsuccessful in tumors greater than 5 cm despite repeated treatments. Survival of patients ranged from 3 to 18 months.

CONCLUSIONS

Percutaneous laser hyperthermia produces significant tumor necrosis and has the advantage of low morbidity, and cost effectiveness. Further refinement is needed to achieve elimination of viable tumor cells at the tumor host interface by further knowledge of appropriate dosimetry levels, manipulation of blood flow and synergistic effects with other therapeutic modalities.

Interstitial laser thermotherapy in the treatment of colorectal liver metastases

Metastatic liver disease is the commonest cause of death in patients with colorectal cancer. A small proportion of these patients (10%) may be treated by surgical resection with five year survival approaching 35-40%. Alternative treatment modalities for localised hepatic disease include in situ ablative techniques that have the advantages of percutaneous application and minimal morbidity. These include Interstitial Laser Thermotherapy (ILT), Radio Frequency Ablation, Percutaneous Microwave therapy, and Focussed Ultrasound Therapy. This article focuses specifically on the development and utilisation of ILT in the treatment of colorectal liver metastases. It provides a review of the pathophysiological factors involved, present status of clinical studies, and future directions. ILT is a safe technique for the treatment of colorectal liver metastases. It may be delivered by minimally invasive techniques to lesions considered unresectable by present criteria. Limitations include the extent and completeness of tumour necrosis achieved as well as imaging techniques. Clinical problems include a lack of controlled studies. Assessment of long-term survival in prospective randomised trials is needed to assess the efficacy of this procedure.

Experimental studies of stereotactic laser balloon hyperthermic treatment

BACKGROUND AND OBJECTIVE

The hyperthermic treatment of small malignant brain tumors in basal ganglia and other eloquent cortical areas was investigated with a stereotactic Nd:YAG laser balloon unit.

STUDY DESIGN/MATERIALS AND METHODS

An Ultra Line fiber (Heraeus Laser Sonics, CA) was inserted into a 6 F silicone balloon catheter, which caused the laser beam to be directed 80 degrees laterally. The balloon was inflated with physiologic saline to make the tumor tissue surrounding the laser fiber hypoxic. The hypoxia enhances the thermal effect on the tumor. The laser power was set at 5 watts (W) and a computer, programmed with specific parameters using feedback control was used to maintain the tissue 10 mm distant from the laser fiber at a temperature of 45 degrees C. Forty five minutes of hyperthermic treatment was applied to an implanted subcutaneous glioma in a rat.

RESULTS/CONCLUSION

The thermally induced damaged in the tumor appeared as a fan-shape lesion extending at a 100 degrees angle from the laser beam axis. The entire tumor could be treated by rotating the laser fiber in the balloon catheter.

Treatment of recurrent colorectal liver metastases by interstitial laser photocoagulation

BACKGROUND

Hepatic resection improves survival in selected patients with colorectal liver metastases. The treatment of recurrent hepatic metastases after resection is controversial. Interstitial laser photocoagulation, performed under local anaesthesia, offers a minimally invasive option to repeat resection. The first series of patients with recurrent colorectal liver metastases treated with photo- coagulation is reported.

METHODS

Nineteen patients (five women and 14 men, median age 57 (range 44-71) years) who developed recurrent colorectal liver metastases after hepatectomy (five with bilateral disease) were treated with photocoagulation between 1993 and 1997. Fifteen patients also received chemotherapy (14 systemic, one hepatic arterial) before photocoagulation.

RESULTS

There were no major complications or deaths related to the treatment. Six patients developed minor complications related to the procedure but did not require any form of intervention. Median survival from commencement of photocoagulation was 16 (range 4-36) months.

CONCLUSION

Photocoagulation is a safe, minimally invasive therapy that may be used as an adjunct to chemotherapy and repeat resection in the treatment of recurrent colorectal liver metastases, and may lead to improved survival.

Simplified treatment planning for interstitial laser thermotherapy by disregarding light transport: a numerical study

BACKGROUND AND OBJECTIVE

The objective was to investigate the effect of light transport on the temperature distribution and the coagulated volume under conditions relevant to interstitial laser thermotherapy (ILT) of tumors in the human liver.

STUDY DESIGN/MATERIALS AND METHODS

Temperature distributions and coagulated volumes produced with a diffusing laser fiber or a conductive heat source, at equal output power, were numerically calculated for tissue with different optical penetration depths. Four irradiation times (5, 10, 20, and 30 min) were studied. A three-dimensional finite-element model was used to calculate the temperature distribution during heating with four conductive heat sources (no light emission). Results were compared with measured temperature distributions during laser irradiation in a gel phantom with known optical properties.

RESULTS

Numerical calculations showed that the influence of light transport on the coagulated volume was negligible in tissue with optical penetration depths below 3-4 mm at all studied irradiation times. The phantom experiment indicated good agreement with the calculated temperature distribution, both with a single diffusing laser fiber and with four fibers.

CONCLUSION

Light transport influences coagulated volumes only slightly under conditions presented in this work, which is relevant to ILT of tumors in the human liver.

Interstitial laser hyperthermia, a new method in the management of fibroadenoma of the breast: A pilot study

BACKGROUND AND OBJECTIVE

This study attempts to evaluate the effect of interstitial laser hyperthermia in breast fibroadenomas as an outpatient procedure.

STUDY DESIGN/MATERIALS AND METHODS

In an uncontrolled prospective study, 27 patients younger than 35 years were subjected to laser phototherapy of their breast fibroadenomas. Under real-time ultrasound monitoring, Nd:YAG laser (1,064 nm wavelength) was used at 2 W for 300 sec (600 J) in a continuous wave mode to produce interstitial hyperthermia. Follow-ups were done at 2, 4, and 8 weeks. Subsequently, excision biopsy of residual lumps was performed.

RESULTS

There was significant decrease in clinical and sonographic sizes (P < 0.001). Follow-up ultrasound showed a progressive change of hyperechoic texture, from a heterogeneous to a nearly homogeneous one. There were minimal scars (2-3 mm) and no keloid or abscess formation.

CONCLUSION

Interstitial laser hyperthermia is a safe, precise, and minimally invasive outpatient procedure for in situ destruction of breast fibroadenomas.

Laser-induced thermotherapy combined with hepatic arterial embolization in the treatment of liver tumors in a rat tumor model

OBJECTIVE

To assess the effect of combined laser-induced thermotherapy (LITT) and hepatic arterial embolization with degradable starch microspheres (DSM) on tumor response and intrahepatic temperature distribution in rats with liver tumors.

SUMMARY BACKGROUND DATA

Laser-induced thermotherapy is a promising in situ ablation technique for malignant liver tumors. However, clinical use is still limited, mainly because of the small size of the inducible coagulation necroses. This results in insufficient tumor destruction.

METHODS

Colon carcinoma CC531 was implanted in 60 WAG rat livers. Fourteen days later, a silicon catheter was implanted in the hepatic artery for DSM administration. Tumors were exposed to 1064 nm Nd:YAG laser light at 2 watts for 10 minutes from a diffuser tip applicator placed in the tumor. The animals were randomized into a sham-operated control (group I) and three test groups. Group II received DSM alone, group III received LITT alone, and group IV received DSM + LITT. Tumor control was examined 1, 7, and 14 days after treatment.

RESULTS

A complete tumor remission was achieved in all rats treated with LITT + DSM (group IV). In contrast, tumor progression was seen in animals treated with LITT alone (group III) or DSM alone (group II), as well as in the sham-operated controls (group I).

CONCLUSIONS

The authors' results suggest that the combination of LITT and DSM considerably increases the efficacy of LITT in the treatment of liver metastases in the rat.

Ultrasound imaging of thermal therapy in in vitro liver

The objective of this work was to image liver tissue heated to temperatures below the vaporization threshold as a function of time, to test the feasibility of real-time ultrasound monitoring to control lesion size during minimally invasive thermal therapy (MITT). Two experiments were devised. In one experiment, a thermal gradient was established in a rectangular volume of tissue to correlate changes in ultrasound image echogenicity (B-mode image brightness) with tissue temperature. In the other, a thermal lesion was produced in a rectangular volume of tissue by an interstitial microwave antenna, and the progression of the lesion was monitored by ultrasound. In both experiments, the echogenicity of the tissue increased slightly for tissue temperatures up to 40 degrees C, but became lower than that of unheated tissue for temperatures above 40 degrees C. In the second experiment, images of the lesion were compared with a photograph of the lesion taken after the experiment was complete. The final lesion was composed of two concentric regions--an inner region of heavily coagulated tissue and an outer region of less-damaged tissue. These two damaged regions indicated that increased ultrasound attenuation was largely responsible for the decreased echogenicity observed in the ultrasound images, and the increase in echogenicity of tissue heated to temperatures up to 40 degrees C is thought to be due to decreased ultrasound attenuation at these temperatures.

Comparison between interstitial laser thermotherapy and excision of an adenocarcinoma transplanted into rat liver

The aim of this study was to compare interstitial laser thermotherapy with excision of a liver tumour. A dimethylhydrazine-induced adenocarcinoma was transplanted (implanted if not stated otherwise) into the left lateral lobe of the rat liver, and treatment was performed 8 days later. In the main experiment, rats were treated with resection of the tumour-bearing lobe or underwent interstitial laser thermotherapy, which was performed at a steady-state temperature of 46 degrees C for 30 min, 3 mm from the tumour margin. The incidence and extent of intraperitoneal spread was smaller after laser thermotherapy than after resection of the tumour-bearing lobe, with no difference in local control. Metastatic spread after resection of the median liver lobe was similar to that observed after sham procedures for thermotherapy or resection, suggesting that the advantage of thermotherapy was not due to a difference in surgical trauma. Additional studies showed that laser thermotherapy reduced intraperitoneal spread when treatment was suboptimal or in a tumour inoculation model and suggested that immunological mechanisms might be involved. It is concluded that interstitial laser thermotherapy reduces spread of liver tumour compared with resection.

Management strategies for colorectal liver metastases--Part II

Liver metastases are relatively common in colorectal cancer and a small proportion of patients may benefit from resection of these liver metastases. In a selected subgroup of patients, 5-year survival rates of 25-35% may be achieved following liver resection. These survival figures compare favourably with those of patients with untreated liver secondaries. In the second part of this review the surgical and non-surgical treatment options for treating colorectal liver metastases are examined in detail.

Determination of laser-induced temperature distributions using echo-shifted TurboFLASH

An echo-shifted TurboFLASH sequence implemented on a clinical whole body MR scanner was used to determine thermal changes in tissue. With this snapshot-like data acquisition, temperature-related phase shifts were measured with a temporal resolution of 1.3 s. For different types of tissue (postmortem porcine brain, liver, and muscle) the temperature coefficients of the proton chemical shift were recorded during uniform heating of the specimen in a water bath. The specific temperature-dependent frequency shifts appeared similar to the proton chemical shift of free water (-0.01 ppm/degrees C). With this method, laser-induced ablation in postmortem porcine brain was monitored by temperature mapping. Comparison of the induced temperature profiles measured with NiCrNi-thermocouples with the MR calculated profiles demonstrated excellent temperature sensitivity and accuracy for this method of MR thermometry, with a maximum deviation of the determined temperatures of only 1.8 degrees C. This investigation was designed as a feasibility study for this rapid version of the phase mapping method, and no in vivo studies were performed.

Liver tumor ablation techniques

Despite advances in surgical technique, patients with primary and secondary liver tumors remain a difficult management problem, as most tumors are unresectable at presentation. Alternative therapies, involving the in situ destruction of liver tumors, have recently come under scrutiny as palliative options. Percutaneous ethanol injection and cryosurgery have been advocated, but both have associated technical difficulties and adverse effects. Novel liver tumor ablation techniques have recently been developed that work via the induction of localized hyperthermia. There is mounting evidence to support a hypothesis that cancer cells are more selectively sensitive to heat than are normal cells, due to the poor blood supply of neoplastic tissue and the decreased vasodilatation capacity of the neovascular bed. These ablative modalities induce a variable degree of tumor necrosis in unresectable tumors, and therefore may provide useful palliation. Clinical trials are needed to determine the true nature and degree of any palliative benefit. In addition, the determinants of treatment efficacy and the predictability of the necrotic zone must be better understood before these techniques can be contemplated as alternatives to liver resection for cure.

Light dosimetry in vivo

This paper starts with definitions of radiance, fluence (rate) and other quantities that are important with regard to in vivo light dosimetry. The light distribution in mammalian tissues can be estimated from model calculations using measured optical properties or from direct measurements of fluence rate using a suitable detector. A historical introduction is therefore followed by a brief discussion of tissue optical properties and of calculations using diffusion theory, the P3-approximation or Monte Carlo simulations. In particular the form of the scattering function is considered in relation to the fluence rate close to the tissue boundary, where light is incident. Non-invasive measurements of optical properties yield the absorption coefficient mu a and mu s(1 - g), where mu s is the scattering coefficient and g is the mean cosine of the scattering angle. An important question is whether this combination is sufficient, or whether g itself must be known. It appears that for strongly forward scattering, as in mammalian tissues, rather detailed knowledge of the scattering function is needed to reliably calculate the fluence rate close to the surface. Deeper in the tissue mu s (1 - g) is sufficient. The construction, calibration and use of fibre-optic probes for measurements of fluence rate in tissues or optical phantoms is discussed. At present, minimally invasive absolute fluence (rate) measurements seem to be possible with an accuracy of 10-20%. Examples are given of in vivo measurements in animal experiments and in humans during clinical treatments. Measurements in mammalian tissues, plant leaves and marine sediments are compared and similarities and differences pointed out. Most in vivo light fluence rate measurements have been concerned with photodynamic therapy (PDT): Optical properties of the same normal tissue may differ between patients. Tumours of the same histological type may even show different optical properties in a single patient. Treatment-induced changes of optical properties may also occur. Scattered light appears to contribute substantially to the light dose. All these phenomena emphasize the importance of in situ light measurements. Another important dosimetric parameter in PDT is the concentration and distribution of the photosensitizer. Apart from in vivo fluorescence monitoring, the photosensitizer part of in vivo PDT dosimetry is still in its infancy.

Colorectal liver metastases

Each year in the UK, between 12-14,000 people develop liver metastases from colorectal cancer. These metastases will contribute to the death of the patient in about 80% of cases. Treatments aimed at these tumours are best administered when the tumour is small. Current investigative methods allow tumours as small as 0.5 mm to be detected, and should be offered to all colorectal cancer patients at risk of developing liver metastases. Surgery remains the only curative treatment for these tumours, but, unfortunately, only 20% of those who have tumour excision will survive five years. In those patients unsuitable for surgery, chemotherapy with fluoropyrimidines produces the best tumour response. This may be administered systemically or regionally, via a catheter placed within the hepatic artery. The latter approach reduces systemic toxicity, but may produce hepatotoxicity. The results of other forms of systemic chemotherapy currently undergoing clinical trials are awaited. The vast majority of patients will benefit from suitable palliative treatment delivered either locally or systemically. With the wide range of treatments now available for liver metastases, these patients are best assessed in a unit with a special interest in the problem.

Nd:YAG laser procedures in tumor treatment

Due to the wide variability of tissue interactions and the possibility of specific applications, the neodymium-yttrium-aluminum-garnet (Nd:YAG) laser is the most important surgical laser. With the adequate choice of application mode and relationship between interaction time and power density, it can be used for precise cutting in the contact mode with the bare fiber, with either a wide or small coagulation seam. With a handpiece a precise focal coagulation for preparation and hemostatic purposes is possible, as well as cutting with the focussed noncontact beam where additionally a wide coagulation seam is necessary. Endoscopically guided coagulation, vaporization, and cutting are possible with bare fibers which can be introduced through nearly all endoscopes. With increasing importance, the possibility for wide and homogeneous volume coagulation is used to destroy diseased tissues either by noncontact irradiation or interstitial placement of the fiber. Thus, the field of laser application in tumor therapy ranges from the treatment of superficial tumors to endoscopic tumor ablation, resection of neoplastic tissue in parenchymatous organs, and interstitial thermotherapy with coagulation of deep-seated primary and secondary malignancies. With its different application modes the laser can be used as a surgical instrument or as a central therapeutical method, whereby perfect control of tissue interactions is always possible by using either visual control for superficial and endoscopic procedures or magnetic resonance imaging and color-coded duplex sonography as a control for interstitial procedures. During 12 years of clinical work we have developed several application modes and have proved the Nd:YAG laser to be an effective instrument in tumor therapy.

Immediate changes in subcellular structures of transplanted tumors following photodynamic and laser hyperthermic therapy

BACKGROUND AND OBJECTIVE

To further understand the precise process of the tumor cell degeneration after photodynamic therapy (PDT), laser hyperthermic therapy (LH), and combined treatments using an Nd:YAG laser. It is important to examine initial morphological alteration of tumor cells after these treatments.

STUDY DESIGN/MATERIALS AND METHODS

In this study, nude mice bearing HeLa cell tumors were treated with PDT, LH, and combined treatments of the two. Tumor tissues obtained immediately after these treatments were analyzed using electron microscopy and morphometry.

RESULTS

In the combined treatments, which produced more severe effects on tumor cells, morphological features of apoptosis such as cytoplasmic condensation, blebs, and apoptotic bodies appeared in the cells, although the typical alteration in the nuclear chromatin was not seen.

CONCLUSION

Cytoplasmic alterations may proceed more rapidly than nuclear alterations in the cellular degeneration induced by the single or combined treatments of PDT and LH.