Interstitial laser thermotherapy in neurosurgery: a review

Laser interstitial thermal therapy in the treatment of brain metastases: the relationship between changes in postoperative magnetic resonance imaging characteristics and tumor recurrence

BACKGROUND

Laser interstitial thermal therapy (LITT) has been used to treat brain metastases (BMs) in several countries, and its safety and effectiveness have been confirmed. In most cases, magnetic resonance imaging (MRI) reveals an increase in tumor volume with an enhanced margin after LITT. However, little is known about the relationship between this MRI change and tumor recurrence.

OBJECTIVE

We report the first case series of BMs treated by LITT in China to evaluate the clinical characteristics and predictive factors of tumor recurrence.

MATERIAL AND METHODS

Patients with less than four brain metastatic lesions and a Karnofsky performance status (KPS) > 70 were eligible for study inclusion. Standard LITT procedures were performed, and a follow-up MRI was performed to analyze the radiographic changes, especially the volume ratio of the enhanced margin and the whole lesion on MRI at 30 days postoperatively. All the volume-related data were delineated and calculated using 3D Slicer software. Related predictors were also collected to evaluate the correlation with local tumor control.

RESULTS

Eighteen patients with nineteen lesions were enrolled for treatment and follow-up. Primary tumor histology included pulmonary carcinoma (n = 11) and breast cancer (n = 4). On average, the tumor size measured 3.01 cm³ (range, 0.40-7.40 cm³), the total ablation time was 13.58 min (range, 2.88-37.15 min), and the complete ablation rate was 92.4% (range, 29.2-100%). Comparing 3s0-day follow-up MRI results with preoperative MRI findings, 18 lesions showed a 2.28-fold (range, 1.21-4.88) volume increase; all the lesions displayed an enhanced component with a volume ratio of 42.35% (range, 10.14-100%). Five patients experienced tumor recurrence, and the local tumor control rates at 90 days and 180 days of follow-up were 68.4% and 66.7%, respectively. Univariate analysis indicated that the primary tumor, ablation rate, and enhanced volume ratio (EVR) > 40% in the 30-day MRI were associated with tumor recurrence, whereas multivariate analysis showed that only EVR > 40% was a predictive factor of local control.

CONCLUSION

LITT is a minimally invasive method used to ablate brain metastases which can be used as the first-line treatment for BM patients under certain indications. After LITT, most tumors showed volume enlargement on the 30-day MRI scan, and EVR > 40% on the 30-day MRI may indicate late tumor recurrence.

Laser hyperthermia: Past, present, and future

Magnetic resonance imaging-guided laser interstitial thermal therapy (LITT) is an ablative procedure using heat from a laser to provide cytoreduction in tissue. It is a minimally invasive procedure that has been used in intracranial pathologies such as high-grade gliomas, metastatic lesions, epilepsy, and other lesions. While LITT may offer a more acceptable complication profile compared to open surgery, the role of laser therapy for intracranial lesions in current treatment paradigms continues to evolve. This review will focus on the background and application of LITT, the current evidence for its use, and future directions for the technology.

Advances in local therapy for glioblastoma - taking the fight to the tumour

Despite advances in neurosurgery, chemotherapy and radiotherapy, glioblastoma remains one of the most treatment-resistant CNS malignancies, and the tumour inevitably recurs. The majority of recurrences appear in or near the resection cavity, usually within the area that received the highest dose of radiation. Many new therapies focus on combatting these local recurrences by implementing treatments directly in or near the tumour bed. In this Review, we discuss the latest developments in local therapy for glioblastoma, focusing on recent preclinical and clinical trials. The approaches that we discuss include novel intraoperative techniques, various treatments of the surgical cavity, stereotactic injections directly into the tumour, and new developments in convection-enhanced delivery and intra-arterial treatments.

Fiber optic probe with functional polymer composites for hyperthermia

We demonstrate a fiber optic probe incorporating functional polymer composites for controlled generation of photothermal effects. The probe combines carbon-based and rare-earth composites on the tip of standard multimode fibers, thus yielding a compact fiber optic photothermal probe (FOPP) whose temperature can be measured simultaneously through fluorescent thermometry. We evaluate the thermal features of the probe through experiments and numerical calculations showing that large thermal gradients are obtained within the vicinity of the heating zone. The temperatures achieved with the FOPP are within the ranges of interest for hyperthermia and can be attained using low optical powers (< 280 mW).

The Management of Brain Metastases-Systematic Review of Neurosurgical Aspects

The multidisciplinary management of patients with brain metastases (BM) consists of surgical resection, different radiation treatment modalities, cytotoxic chemotherapy, and targeted molecular treatment. This review presents the current state of neurosurgical technology applied to achieve maximal resection with minimal morbidity as a treatment paradigm in patients with BM. In addition, we discuss the contribution of neurosurgical resection on functional outcome, advanced systemic treatment strategies, and enhanced understanding of the tumor biology.

Epilepsy surgery in tuberous sclerosis complex (TSC): emerging techniques and redefinition of treatment goals

Epilepsy occurs in nearly all patients with tuberous sclerosis and is often refractory to medical treatment. The definition of surgical candidacy in these patients has broadened in recent years due to philosophical and technological advances. The goals of surgery have shifted to focusing on quality of life and maximizing neurodevelopmental potential in patients unable to obtain seizure freedom. Novel diagnostic, ablative, and neuromodulatory techniques have been developed that may help patients that were previously considered inoperable to have an improved quality of life. In the coming years, it is expected that these techniques will be further refined and lead to an improvement of neurological prognosis in patients with tuberous sclerosis.

Laser interstitial thermal therapy

Background

Laser interstitial thermal therapy (LITT) is becoming an increasingly popular technique for the treatment of brain lesions. More minimally invasive that open craniotomy for lesion resection, LITT may be more appropriate for lesions that are harder to access through an open approach, deeper lesions, and for patients who may not tolerate open surgery.

Methods

A search of the current primary literature on LITT for brain lesions on PubMed was performed. These studies were reviewed and updates on the radiological, pathological, and long-term outcomes after LITT for brain metastases, primary brain tumors, and radiation necrosis as well as common complications are included.

Results

Larger extent of ablation and LITT as frontline treatment were potential predictors of favorable progression-free and overall survival for primary brain tumors. In brain metastases, larger extent of ablation was more significantly associated with survival benefit, whereas tumor size was a possible predictor. The most common complications after LITT are transient and permanent weakness, cerebral edema, hemorrhage, seizures, and hyponatremia.

Conclusions

Although the current literature is limited by small sample sizes and primarily retrospective studies, LITT is a safe and effective treatment for brain lesions in the correct patient population.

Thermal ablation of pancreatic cancer: A systematic literature review of clinical practice and pre-clinical studies

PURPOSE

Pancreatic cancer is a challenging malignancy with low treatment option and poor life expectancy. Thermal ablation techniques were proposed as alternative treatment options, especially in advanced stages and for unfit-for-surgery patients. This systematic review describes the thermal ablative techniques -i.e., Laser (LA), Radiofrequency (RFA), Microwave (MWA) Ablation, High-Intensity Focused Ultrasound (HIFU) and cryoablation- available for pancreatic cancer treatment. Additionally, an analysis of the efficacy, complication rate and overall survival for each technique is conducted.

MATERIAL AND METHODS

This review collects the ex vivo, preclinical and clinical studies presenting the use of thermal techniques in the pancreatic cancer treatment, searched up to March 2018 in PubMed and Medline. Abstracts, letters-to-the-editor, expert opinions, reviews and non-English language manuscripts were excluded.

RESULTS

Sixty-five papers were included. For the ex vivo and preclinical studies, there are: 12 records for LA, 8 for RFA, 0 for MWA, 6 for HIFU, 1 for cryoablation and 3 for hybrid techniques. For clinical studies, 1 paper for LA, 14 for RFA, 1 for MWA, 17 for HIFU, 1 for cryoablation and 1 for hybrid techniques.

CONCLUSIONS

Important technological advances are presented in ex vivo and preclinical studies, as the real-time thermometry, nanotechnology and hybrid techniques to enhance the thermal outcome. Conversely, a lack of standardization in the clinical employment of the procedures emerged, leading to contrasting results on the safety and feasibility of some analyzed techniques. Uniform conclusions on the safety and feasibility of these techniques for pancreatic cancer will require further structured investigation.

Comparative Evaluation of Magnetic Resonance-Guided Focused Ultrasound Surgery for Essential Tremor

BACKGROUND

Treatment options for patients with drug-resistant essential tremor (ET) are limited. Magnetic resonance-guided focused ultrasound surgery (MRgFUS) is an emerging technique to treat refractory ET.

OBJECTIVES

To present MRgFUS as an alternative to radiofrequency (RF) thalamotomy or deep brain stimulation (DBS) for ET treatment.

METHODS

We retrospectively analyzed 59 patients who underwent unilateral surgery for drug-resistant ET. Treatments included RF thalamotomy (n = 17), DBS (n = 19), and MRgFUS (n = 23). The outcomes measured were tremor severity and treatment-related complications.

RESULTS

At 1 month postoperatively, 100% of RF thalamotomy patients, 89.5% of DBS patients, and 91.3% of MRgFUS patients exhibited absent/mild tremor (successful treatment); other patients exhibited partial relief. At 12 months postoperatively, treatment success for each procedure was observed in 70.6, 84.2, and 78.3% of patients, respectively. At 1 month postoperatively, treatment-related complications had occurred in 58.8, 5.3, and 13.0% of patients, respectively. At 12 months postoperatively, side effects persisted in 11.8, 21.1, and 4.4% of patients, respectively. No statistical differences in treatment success were observed between treatments or over time. Complication rates differed between treatment modalities (p < 0.01) and were lowest in the MRgFUS group.

CONCLUSIONS

Patients with drug-resistant ET received equivalent results from RF thalamotomy, DBS, and MRgFUS. DBS and MRgFUS resulted in fewer treatment-related complications.

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.

Numerical and ex vivo studies of a bioprobe developed for laser-induced thermotherapy (LITT) in contact with liver tissue

This work is based on the production of a bioprobe that is compatible with magnetic resonance imaging (MRI) for laser-induced thermotherapy (LITT) in liver cancer laser therapy. This probe is made of an alumina tube (3-mm diameter) in which an optical fibre is centred and fixed. A shooting window (20mm) is created using a mechanical rectifier. The device is then consolidated by the injection of a transparent and heat-resistant resin. Through numerical modelling, the thermal power damping of the laser source is evaluated as well as the propagation of the heat in the ex vivo liver tissue according to different heating scenarios. These analyses allow for an estimation of the irradiated volume. Ex vivo tests were performed on bovine liver to confirm the adequacy of the bioprobe for LITT and of the irradiated volumes predicted by the numerical model. There was a difference of 8% between the simulations and ex vivo experiments. The pulsed mode heating scenario was the most effective under the experimental conditions.

Photothermal lesions in soft tissue induced by optical fiber microheaters

Photothermal therapy has shown to be a promising technique for local treatment of tumors. However, the main challenge for this technique is the availability of localized heat sources to minimize thermal damage in the surrounding healthy tissue. In this work, we demonstrate the use of optical fiber microheaters for inducing thermal lesions in soft tissue. The proposed devices incorporate carbon nanotubes or gold nanolayers on the tips of optical fibers for enhanced photothermal effects and heating of ex vivo biological tissues. We report preliminary results of small size photothermal lesions induced on mice liver tissues. The morphology of the resulting lesions shows that optical fiber microheaters may render useful for delivering highly localized heat for photothermal therapy.

Sciatic nerve repair using adhesive bonding and a modified conduit

When repairing nerves with adhesives, most researchers place glue directly on the nerve stumps, but this method does not fix the nerve ends well and allows glue to easily invade the nerve ends. In this study, we established a rat model of completely transected sciatic nerve injury and repaired it using a modified 1 cm-length conduit with inner diameter of 1.5 mm. Each end of the cylindrical conduit contains a short linear channel, while the enclosed central tube protects the nerve ends well. Nerves were repaired with 2-octyl-cyanoacrylate and suture, which complement the function of the modified conduit. The results demonstrated that for the same conduit, the average operation time using the adhesive method was much shorter than with the suture method. No significant differences were found between the two groups in sciatic function index, motor evoked potential latency, motor evoked potential amplitude, muscular recovery rate, number of medullated nerve fibers, axon diameter, or medullary sheath thickness. Thus, the adhesive method for repairing nerves using a modified conduit is feasible and effective, and reduces the operation time while providing an equivalent repair effect.

Advances in therapy for melanoma brain metastases

Melanoma cells frequently metastasize to the brain, and approximately 50% of patients with metastatic melanoma develop intracranial disease. Historically, central nervous system dissemination has portended a very poor prognosis. Recent advances in systemic therapies for melanoma, supported by improved local therapy control of brain lesions, have resulted in better median survival for these patients. We review current local and systemic approaches for patients with melanoma brain metastases.

Stereotactic laser induced thermotherapy (LITT): a novel treatment for brain lesions regrowing after radiosurgery

Since the inception of radiosurgery, the management of brain metastases has become a common problem for neurosurgeons. Although the use of stereotactic radiosurgery and/or whole brain radiation therapy serves to control the majority of disease burden, patients who survive longer than 6-8 months sometimes face the problem of symptomatic radiographically regrowing lesions with few treatment options. Here we investigate the feasibility of use of MRI-guided stereotactic laser induced thermotherapy (LITT) as a novel treatment option for these lesions. Six patients who had previously undergone gamma knife stereotactic radiosurgery for brain metastases were selected. All patients had an initial favorable response to radiosurgery but subsequently developed regrowth of at least one lesion associated with recurrent edema and progressive neurological symptoms requiring ongoing steroids for symptom control. All lesions were evaluated for craniotomy, but were deemed unresectable due to deep location or patient's comorbidities. Stereotactic biopsies were performed prior to the thermotherapy procedure in all cases. LITT was performed using the Visualase system and follow-up MRI imaging was used to determine treatment response. In all six patients biopsy results were negative for tumor and consistent with adverse radiation effects also known as radiation necrosis. Patients tolerated the procedure well and were discharged from the hospital within 48 h of the procedure. In 4/6 cases there was durable improvement of neurological symptoms until death. In all cases steroids were weaned off within 2 months. One patient died from systemic causes related to his cancer a month after the procedure. One patient had regrowth of the lesion 3 months after the procedure and required re-initiation of steroids and standard craniotomy for surgical resection. There were no complications directly related to the thermocoagulation procedure. Stereotactic laser induced thermotherapy is a feasible alternative for the treatment of symptomatic regrowing metastatic lesions after radiosurgery. The procedure carries minimal morbidity and, in this small series, shows some effectiveness in the symptomatic relief of edema and neurological symptoms paralleled by radiographic lesional control. Further studies are necessary to elucidate the safety of this technology.

Laser-induced thermotherapy for lung tissue—evaluation of two different internally cooled application systems for clinical use

Thermal ablation techniques like radiofrequency or laser-induced thermotherapy (LITT) are increasingly used to treat tumors of parenchymatous organs. Minimal access, parenchymal preservation, and a low complication rate render them suitable for pulmonary tumors as well. Their successful clinical application depends on the induction of sufficiently large lesions and a knowledge of the energy parameters required for complete thermal ablation. The aim of this study was to establish a dose-response relationship for a percutaneous and an intraoperative system for LITT of lung tissue. Thermal lesions were induced in healthy porcine lungs using an Nd:YAG laser (1,064 nm). LITT was performed with a percutaneous application system in group I (n = 18) and an intraoperative application system in group II (n = 90). Laser energy was applied for 600-1,200 s in a power range of 20-32 W (12,000-38,400 J). The lesions were longitudinally and transversally measured, and the volume was calculated after the intervention. Furthermore, an open application system was used to perform LITT under in vivo conditions during lung perfusion and ventilation in domestic pigs. Lesion volumes in both groups showed a plateau-like curve when the laser power increased from an initial level of 25 W. With the percutaneous puncture system (group I), the application of 28 W (16,800 J) for 10 min generated the largest lesions with a volume of 12.54 +/- 1.33 cm(3), an axial diameter of 39.33 +/- 2.52 mm, and a diametrical diameter of 24.67 +/- 1.15 mm. A longer application time was not possible due to thermal instability of the applicator. Moreover, group I started developing extensive carbonizations at a laser power of 22 W (13,200 J). The intraoperative application system (group II) achieved the largest lesion volumes of 11.03 +/- 2.54 cm(3) with diameters of 34.6 +/- 4.22 mm (axial) and 25.6 +/- 2.51 mm (diametrical) by an exposure time of 20 min and a power of 32 W (38,400 J). Here extensive carbonizations only started to occur at 28 W (33,600 J). Under in vivo conditions, all pigs tolerated the LITT procedure well without complications. Besides a typical cooling effect in the vicinity of blood vessels, the thermal lesions were about three times smaller than the ex vivo lesions. Both the percutaneous and the open LITT application system induced reproducible, clinically relevant lung lesions. The percutaneous puncture set generated large relevant lesions, although its usability is limited by its restricted capacity and high carbonization risk. It is suitable for powers up to 22 W. The intraoperative application system allows higher energy exposure to induce larger lesion volumes. This study elucidates the dose-effect relation of two clinically relevant puncture sets.

NEUROGATE: a new MR-compatible device for realizing minimally invasive treatment of intracerebral tumors

The authors report on the handling and the practicability of a newly developed MR-compatible device, the NEUROGATE (Daum GmbH, Germany), which allows precise planning, simulation and control of stereotactic biopsy in patients with suspect intracranial lesions, and which allows minimally invasive maneuvers to be performed in a comfortable way. Twenty-eight patients were examined stereotactically in the Signa SP interventional 0.5 Tesla MRI (General Electric Medical Systems, USA), including 15 patients with malignant intracerebral tumors and poor general medical conditions (8 gliomas, 7 metastases) who were treated by laser-induced interstitial thermotherapy (LITT) after definite intraoperative neuropathological diagnosis. As a special stereotactic holding device, the NEUROGATE was favored as a reliable tool for stereotaxy and minimally invasive procedures.

Mild heat shock induces autophagic growth arrest, but not apoptosis in U251-MG and U87-MG human malignant glioma cells

Although hyperthermia has been used as a treatment of malignant brain tumors, it is not yet clear what is the mechanism of the cell growth inhibition by heat shock, especially by the temperature which has clinically been applied to tumor-brain border-zone, 42-43 degrees C. Therefore, we evaluated the change of U251-MG and U87-MG human malignant glioma cells after 43 degrees C-heat shock comparing with that of 45 degrees C. First, we observed that cell growth was transiently inhibited after 43 degrees C-heat shock for 3 or 5 days, in U251-MG or U87-MG cells, respectively, which was followed by regrowth. During the period of transient growth inhibition, mild G2/M arrest was observed. However, apoptosis was observed in only 2.7% or 1.5%, of 43 degrees C-heated cells, in U251-MG or U87-MG cells, respectively. Instead, transmission electron micrography showed the formation of vacuoles, degeneration of mitochondria, and autophagosomes. Moreover, in the both cell lines, flow-cytometric analysis with acridine orange revealed the induction of acidic vesicle organelles, which was blocked by 3-methyladenine (3-MA), suggesting the involvement of autophagy. Furthermore, while 3-MA did not increase the anti-tumor effect of 43 degrees C-heat shock, bafilomycin A1, another autophagy inhibitor, did significantly enhance the effect in U251-MG cells. Taken together, mild heat shock (43 degrees C for 2 h) causes autophagy and mild G2/M arrest, but does not induce apparent apoptosis in U251-MG and U87-MG glioma cells. Inhibition of autophagy with bafilomycin A1 may increase the anti-tumor efficacy of mild heat shock against some malignant glioma cells.

Multi-modality tissue-mimicking phantom for thermal therapy

A tissue-mimicking phantom material has been developed for use with thermal therapy devices and techniques. This material has magnetic resonance properties (primarily T2) which change drastically upon thermal coagulation, enabling its use for device characterization and treatment verification using simple T2-weighted imaging techniques. The coagulation temperature of the phantom can be changed from 50-60 degrees C by adjusting the pH from 4.3 to 4.7. The energy absorption properties can be adjusted to match the acoustical and optical properties of tissues. T2 relaxation measurements are provided as a function of temperature, along with T2-weighted MR images to illustrate the visualization of heating patterns. A complete recipe for fabricating phantoms is provided.

Locoregional opening of the rodent blood-brain barrier for paclitaxel using Nd:YAG laser-induced thermo therapy: a new concept of adjuvant glioma therapy?

BACKGROUND AND OBJECTIVES

Nd:YAG laser-induced thermo therapy (LITT) of rat brains is associated with blood-brain barrier (BBB) permeability changes. We address the question of whether LITT-induced locoregional disruption of the BBB could possibly allow a locoregional passage of chemotherapeutic agents into brain tissue to treat malignant glioma.

STUDY DESIGN/MATERIALS AND METHODS

CD Fischer rats were subject to LITT of the left forebrain. Disruption of the BBB was analyzed using Evans blue and immunohistochemistry (IH). Animals were perfused with paclitaxel, and high-pressure liquid chromatography (HPLC) was employed to analyze the content of paclitaxel in brain and plasma samples.

RESULTS

LITT induces an opening of the BBB as demonstrated by locoregional extravasation of Evans blue, C3C, fibrinogen, and IgM. HPLC proved the passage of paclitaxel across the disrupted BBB.

CONCLUSIONS

LITT induces a locoregional passage of chemotherapeutic agents into the brain tissue. This is of potential interest for the treatment of brain tumors.

Kryotherapie am Hirn – ein neuer methodischer Ansatz

Cryodestruction of tissue is influenced by cooling and thawing rates, absolute tissue temperature, number of freeze-thaw cycles, and type of tissue. However, under clinical conditions a MRT visualization of the temperature distribution during cryo-procedures is not possible. Thus, the extent of necrotic areas within the cryo-influenced regions are not precisely predictable. This limitation is particularly relevant for the application of cryoablation in the brain. The present paper proposes the concept of a local, cryo-induced ischemic necrosis. The basic concept is that the MRT-observable and surgically well-manageable frozen region is ischemic. This cryo-induced ischemia causes a necrosis. The extent of the necrotic region is exclusively determined by the ischemia tolerance of the tissue. The effectiveness of this method is demonstrated on sheep brain in vivo. Compared to the freeze-thaw method, histological examinations show a sharper demarcation between regions of necrosis and healthy tissue. In conclusion, the method of MR-controlled local, cryo-induced ischemia enables an exact definition of the region of necrosis in the brain.

Control of interstitial thermal coagulation: comparative evaluation of microwave and ultrasound applicators

This study presents a comparative evaluation of the control of heating and thermal coagulation with microwave (MW) and ultrasound (US) interstitial applicators. Helical coil MW antennas (17 mm and 25 mm length radiating antennae) were tested using an external implant catheter (2.2 mm o.d.) with water-cooling. US applicators with tubular transducers (2.2 and 2.5 mm o.d., 10 mm length, single-element and 3-element) were utilized with a direct-coupled configuration and internal water-cooling. Measurements of E-field distributions (for MW) and acoustic beam distributions (for US) were used to characterize the applicator energy output. Thermal performance was evaluated through multiple heating trials in vitro (bovine liver) and in vivo (porcine thigh muscle and liver) at varied levels of applied power (20-40 W for microwave, 15-35 W for ultrasound) and heating times (0.5-5 min). Axial temperature distributions in the tissue were recorded during heating, and dimensions of the resulting lesions of thermal coagulation were measured. Both MW and US applicators produced large volumes of tissue coagulation ranging from 8 to 20 cm3 with singular heating times of 5 min. Radial depth of lesions for both MW and US applicators increased with heating duration and power levels, though US produced notably larger lesion diameters (30-42 mm for US vs 18-26 mm for MW, 5 min heating). Characteristic differences between the applicators were observed in axial energy distribution, tissue temperatures, and thermal lesion shapes. MW lesions increased significantly in axial dimensions (beyond the active applicator length) as applied power level and/or heating duration was increased, and lesion shapes were generally not uniform. US provided greater control and uniformity of heating, with energy deposition and axial extent of thermal lesions corresponding to the length of the active transducer(s). The improved ability to control the extent of thermal coagulation demonstrated by the US applicators provides greater potential to target a specific region of tissue.

Development of stereotactically guided laser interstitial thermotherapy of breast cancer: in situ measurement and analysis of the temperature field in ex vivo and in vivo adipose tissue

BACKGROUND AND OBJECTIVE

The size (0.5-1.0 cm) of early nonpalpable breast tumors currently detected by mammography and confirmed by stereotactic core biopsy is of the order of the penetration depth of near infrared photons in breast tissue. In principle, stereotactically biopsied tumors, therefore, could be safely and efficiently treated with laser thermotherapy. The aim of the current study is to confirm the controlled heating produced by clinically relevant power levels delivered with an interstitial laser fiber optic probe adapted for use with stereotactic mammography and biopsy procedures.

STUDY DESIGN/MATERIALS AND METHODS

Temperature increases and the resultant thermal field produced by the irradiation of ex vivo (porcine and human) and in vivo (porcine) tissue models appropriate to the treatment of human breast tissue by using cw Nd:YAG laser radiation delivered with a interstitial fiber optic probe with a quartz diffusing tip, were recorded with an array of fifteen 23-gauge needle thermocouple probes connected to a laboratory computer-based data acquisition system.

RESULTS

By using a stepwise decreasing power cycle to avoid tissue charring, acceptably symmetric thermal fields of repeatable volumetric dimensions were obtained. Reproducible thermal gradients and predictable tissue necrosis without carbonization could be induced in a 3-cm-diameter region around the fiber probe during a single treatment lasting only 3 minutes. The time-dependences of the temperature rise of the thermocouples surrounding the LITT probe were quantitatively modeled with simple linear functions during the applied laser heating cycles.

CONCLUSION

Analysis of our experimental results show that reproducible, symmetric and predictable volumetric temperature increases in time can be reliably produced by interstitial laser thermotherapy.

Axial control of thermal coagulation using a multi-element interstitial ultrasound applicator with internal cooling

A multi-element, direct-coupled ultrasound (US) applicator with internal water cooling was investigated for axial control of interstitial thermal coagulation. A prototype implantable applicator was constructed with a linear array of three tubular PZT ultrasound transducers (each 2.5 mm OD, 10 mm length, 360 degrees emittance). Acoustic beam distributions from each element were measured and found to be collimated within the transducer length. The internally cooled applicator could sustain high levels of applied power to each transducer (0 to 40 W) and maintain acceptable applicator surface temperatures (<100 degrees C). Thermal performance of the applicator was investigated through heating trials in vivo (porcine thigh muscle and liver) and in vitro (bovine liver). The radial depth of thermal lesions produced was dependent on the applied power and sonication time and was controlled independently with power levels to each transducer element. With 18 W per element (applied electrical power) for 3 min, cylindrical thermal lesions were produced with a diameter of ~3 cm and a length ranging from 1.2 cm (with one element) to 3.5 cm (three elements). Higher powers (24 to 30 W) for 3 to 5 min provided increased depths of coagulation (~4 cm diameter lesions). Analysis of axial lesion shapes demonstrated that individual variation of power to each transducer element provided control of axial heating and depth of coagulation (for custom lesion shapes); lesion lengths corresponded to the number of active transducers. This ability to control the heating distribution dynamically along the length of the applicator has potential for improved target localization of thermal coagulation and necrosis in high temperature thermal therapy.

Ultrasound applicators for interstitial thermal coagulation

Direct-coupled (DC) and catheter-cooled (CC) ultrasound applicator configurations were evaluated for high-temperature ultrasound interstitial thermal therapy (USITT) using computer simulations, acoustic beam measurements, and in vivo temperature measurements. The DC devices consist of 2.2-mm diameter tubular ultrasound transducers encapsulated within a thin biocompatible plastic coating, which can be inserted directly into the tissue. The CC devices incorporate 1.5-mm diameter tubular transducers, which are inserted within 2.2to 2.4-mm diameter plastic implant catheters and require an integrated water-cooling scheme. Simulated transient temperature profiles and cumulative thermal dose distributions indicate that each of these applicator configurations can produce target temperatures greater than 50 degrees C and corresponding thermal doses greater than 300 to 600 equivalent minutes at 43 degrees C (EM(43 degrees C)) within 5 min at a radial depth of 1 to 1.5 cm in moderately perfused tissues. Theoretical investigations of air-cooling implemented within DC applicators demonstrated a significant enhancement of thermal penetration compared with non-cooled DC applicators, thus approaching performance attainable with CC devices. Temperature distributions achieved with DC and CC applicators in vivo were in agreement with theoretical calculations and further demonstrate that the devices are practical, sufficient power output levels can be obtained, and the angular heating profiles can be shaped or directed to protect non-targeted critical normal tissues. This preliminary study demonstrates that these interstitial ultrasound applicators have potential to provide controlled thermal coagulation and necrosis of small target regions and deserve further investigation and development for possible implementation in the treatment of benign and cancerous lesions in sites such as prostate, liver, and brain.