Interstitial Nd:YAG laser coagulation with a cylindrical diffusing fiber tip in experimental liver metastases

Microfocusing sapphire capillary needle for laser surgery and therapy: Fabrication and characterization

A sapphire shaped capillary needle designed for collimating and focusing of laser radiation was proposed and fabricated by the edge-defined film-fed growth technique. It features an as-grown surface quality, high transparency for visible and near-infrared radiation, high thermal and chemical resistance and the complex shape of the tip, which protects silica fibers. The needle's geometrical parameters can be adjusted for use in various situations, such as type of tissue, modality of therapy and treatment protocol. The focusing effect was demonstrated numerically and observed experimentally during coagulation of the ex vivo porcine liver samples. This needle in combination with 0.22NA optical fiber allows intensive and uniform coagulation of 150 mm³ volume interstitially and 30 mm³ superficially by laser exposure with 280 J without tissue carbonization and fiber damaging along with delicate treatment of small areas. The demonstrated results reveal the perspectives of the proposed sapphire microfocusing needle for laser surgery and therapy.

Magnetic Resonance Imaging-Guided Breast Interventions: Role in Biopsy Targeting and Lumpectomies

Contrast-enhanced breast MR imaging is increasingly being used to diagnose breast cancer and to perform biopsy procedures. The American Cancer Society has advised women at high risk for breast cancer to have breast MR imaging screening as an adjunct to screening mammography. This article places special emphasis on biopsy and operative planning involving MR imaging and reviews use of breast MR imaging in monitoring response to neoadjuvant chemotherapy. Described are peer-reviewed data on currently accepted MR imaging-guided procedures for addressing benign and malignant breast diseases, including intraoperative imaging.

Comparison of laser-induced damage with forward-firing and diffusing optical fiber during laser-assisted lipoplasty

BACKGROUND AND OBJECTIVES

Laser-assisted lipoplasty is made possible by using an optical fiber that delivers light endoscopically to subcutaneous fat tissue. Most optical fibers for laser-assisted lipoplasty are designed to be irradiated in a forward direction. In this study, we compared forward-firing fiber and diffusing fiber for use in laser-assisted lipoplasty. The effective parameters of the ablation pattern which resulted from the laser-induced damage are discussed for both systems. In particular, we note the effect resulting from the different beam emission patterns and the contours of laser fluence.

METHODS

We used two different laser delivery systems (a forward-firing fiber and a diffusing fiber) to examine how the beam emission pattern affects the laser-assisted coagulation and damage pattern of in vitro fat tissues. A porcine liver tissue (water-rich tissue) was used as a secondary laser target to investigate how the laser-assisted coagulation pattern depends on both the type of tissue (water-rich and lipid-rich tissue) as well as the delivery system. An evaluation using a digital camera and a thermal camera was conducted for the tissue ablation processes in order to observe the generated heat transfer in fat and liver.

RESULTS

The overall shape of the laser-assisted coagulation zone was different from the beam emission pattern in the case where a forward-firing fiber was used within fat tissue. The center of the laser-affected zone is characterized by the formation of a reservoir of melted fat. In the thermal image analysis, there existed a discrepancy between the temperature distribution of the fat tissue and the liver tissue during the forward-firing fiber irradiation. In the liver tissue ablation process, the temperature distribution during the laser ablation also demonstrated an elongated ellipse that matches well with the laser-induced damage zone. The temperature distribution in fat tissue adhered to a more discoid pattern that corresponded to the laser-induced damage zone.

CONCLUSIONS

Based on our findings, we have proposed mechanisms that can explain the laser-induced damage in both tissues when a forward firing fiber is employed as the delivery system. In the case of fat tissue, the ablation mechanism can be characterized by the reservoir formation of melted lipids while the ablation is characterized as the well-known drilling effect for liver tissue.

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.

Percutaneous Laser Ablation in the Treatment of Toxic and Pretoxic Nodular Goiter

OBJECTIVE

To report data regarding treatment with use of percutaneous laser ablation (PLA) in autonomously functioning thyroid nodules (AFTN).

METHODS

We treated 18 patients (10 women and 8 men, 31 to 80 years old) who presented with a single hyperfunctioning thyroid nodule (8 patients) or a multi-nodular goiter (10 patients) with clearly hyperfunctioning areas on a thyroid scintiscan. In 5 cases, free thyroxine (FT4) and free triiodothyronine (FT3) levels were high, and in these patients and a further 9 patients with cardiovascular symptoms, methimazole therapy was initiated to restore euthyroidism. The total number of PLA sessions ranged from 1 to 5 (median, 3). Thyroid-stimulating hormone, FT4, FT3, thyroglobulin, and antithyroglobulin and anti-thyroid peroxidase antibodies were measured by a commercial kit the day after PLA treatment, then weekly during the first month, and monthly thereafter. The Student t test was used for statistical analyses, and data are reported as mean values +/- SE.

RESULTS

After each PLA session, there was a transient and mild increase in FT4 and FT3-5.2% to 18.1% (mean, 11.1 +/- 0.69%) (P<0.001) in patients not treated with methimazole and 4.0% to 8.3% (mean, 5.9 +/- 0.31%) (P<0.001) in patients treated with methimazole-relative to values before treatment; however, these values never reached the range of hyperthyroidism. In addition, thyroglobulin showed a remarkable increase after 24 hours- 115% to 390% (mean, 266.0 +/- 12.7%) (P<0.001). Thyroid-stimulating hormone increased in all cases and reached normal values in all patients with single AFTN and in 5 patients (50%) with multinodular goiter within 3 months after PLA. At 1-year follow-up, the decrease in nodular volume was 24% to 72% (mean, 59.3 +/- 8.2%; P<0.001).

CONCLUSION

Our data show that PLA can be a useful treatment in AFTN and particularly in single toxic nodules. Possible elective indications are patients who refuse surgical or radioiodine treatment and patients with cardiovascular comorbidity who need rapid restoration of the euthyroid state and who cannot tolerate the discontinuation of antithyroid drugs for radioiodine treatment.

Adrenal metastases: CT-guided and MR-thermometry-controlled laser-induced interstitial thermotherapy

The aim of the study was to evaluate the feasibility, safety and effectiveness of CT-guided and MR-thermometry-controlled laser-induced interstitial thermotherapy (LITT) in adrenal metastases. Nine patients (seven male, two female; average age 65.0 years; range 58.7-75.0 years) with nine unilateral adrenal metastases (mean diameter 4.3 cm) from primaries comprising colorectal carcinoma (n = 5), renal cell carcinoma (n = 1), oesophageal carcinoma (n = 1), carcinoid (n = 1), and hepatocellular carcinoma (n = 1) underwent CT-guided, MR-thermometry-controlled LITT using a 0.5 T MR unit. LITT was performed with an internally irrigated power laser application system with an Nd:YAG laser. A thermosensitive, fast low-angle shot 2D sequence was used for real-time monitoring. Follow-up studies were performed at 24 h and 3 months and, thereafter, at 6-month intervals (median 14 months). All patients tolerated the procedure well under local anaesthesia. No complications occurred. Average number of laser applicators per tumour: 1.9 (range 1-4); mean applied laser energy 33 kJ (range 15.3-94.6 kJ), mean diameter of the laser-induced coagulation necrosis 4.5 cm (range 2.5-7.5 cm). Complete ablation was achieved in seven lesions, verified by MR imaging; progression was detected in two lesions in the follow-up. The preliminary results suggest that CT-guided, MR-thermometry-controlled LITT is a safe, minimally invasive and promising procedure for treating adrenal metastases.

Synergistic effect of interstitial laser coagulation and doxorubicin in a murine tumor recurrence model of solitary colorectal liver metastasis

BACKGROUND

Interstitial laser coagulation (ILC) is gaining acceptance for treatment of unresectable colorectal liver metastases. However, local recurrence rates are still high. To overcome this problem, we investigated the potential of additional systemic therapy after ILC in a murine model.

METHODS

Single C26 colon carcinoma nodules (approximately 1 mm3) expressing firefly luciferase were implanted in the left liver lobe of 32 BALB/c mice. Seven days after implantation, tumors were treated with either ILC alone (neodymium-yttrium aluminum garnet; 6 W/cm; 800 J/cm) or ILC followed by 1 mg/kg of doxorubicin intravenously. Controls received either doxorubicin alone or sham treatment. Tumor load was measured by in vivo bioluminescent imaging.

RESULTS

Solitary colorectal liver metastases developed over 7 days after tumor implantation in the liver. Extrahepatic disease was not observed. The ILC dose was set to ablate the liver metastases with recurrent tumor growth in 9 of 16 mice after 7 days. After ILC plus doxorubicin, complete tumor destruction occurred without recurrence (0 of 14). Sham treatment or treatment with doxorubicin alone showed an exponential increase in tumor load.

CONCLUSIONS

A murine tumor recurrence model after local ablative treatment of solitary liver metastasis was developed. The combination of ILC and doxorubicin had a strong synergistic effect that led to complete tumor remission in all animals treated.

Enhancement of the immune response to residual intrahepatic tumor tissue by laser-induced thermotherapy (LITT) compared to hepatic resection

BACKGROUND AND OBJECTIVES

In contrast to hepatic resection, thermally destroyed autologous tumor cells remain in situ after laser-induced thermotherapy (LITT). The aim of the study was to evaluate the effect of LITT and hepatic resection on the immune response to residual intrahepatic tumor tissue and the growth of untreated liver metastases.

STUDY DESIGN/MATERIALS AND METHODS

Two independent adenocarcinomas (CC531) were implanted into 60 WAG rats, one in the right (control tumor) and one in the left liver lobe (treated tumor). The left lobe tumor was treated either by LITT or partial hepatectomy. The control tumor was submitted to further investigation 24 hours, 96 hours, 7 days, and 10 days after treatment.

RESULTS

Ten days after treatment, control tumor volumes were 296+/-46 mm_ after LITT and 1,181+/-192 mm_, 1,387+/-200 mm_ after hepatic resection and no treatment, respectively (P<0.001). Peritoneal tumor spread was detected in 4/20 cases after LITT and in 17/20 cases after hepatic resection. Expression of CD8, B7-2 (CD86), and to lesser extent MHCII, LFA1 (CD11a), and ICAM1 (CD54), was significantly enhanced at the invasion front of control tumors after LITT compared to hepatic resection.

CONCLUSIONS

Our results suggest that LITT increases the immune response against untreated intrahepatic tumor tissue, which can lead to reduced tumor growth.

Mechanisms of Focal Heat Destruction of Liver Tumors

BACKGROUND

Focal heat destruction has emerged as an effective treatment strategy in selected patients with malignant liver tumors. Radiofrequency ablation, interstitial laser thermotherapy, and microwave treatment are currently the most widely applied thermal ablative techniques. A major limitation of these therapies is incomplete tumor destruction and overall high recurrences. An understanding of the mechanisms of tissue injury induced by focal hyperthermia is essential to ensure more complete tumor destruction. Here, the currently available scientific literature concerning the underlying mechanisms involved in the destruction of liver tumors by focal hyperthermia is reviewed.

METHODS

Medline was searched from 1960 to 2004 for literature regarding the use of focal hyperthermia for the treatment of liver tumors. All relevant literature was searched for further references.

RESULTS

Experimental evidence suggests that focal hyperthermic injury occurs in two distinct phases. The first phase results in direct heat injury that is determined by the total thermal energy applied, tumor biology, and the tumor microenvironment. Tumors are more susceptible to heat injury than normal cells as the result of specific biological features, reduced heat dissipating ability, and lower interstitial pH. The second phase of hyperthermic injury is indirect tissue damage that produces a progression of tissue injury after the cessation of the initial heat stimulus. This progressive injury may involve a balance of several factors, including apoptosis, microvascular damage, ischemia-reperfusion injury, Kupffer cell activation, altered cytokine expression, and alterations in the immune response. Blood flow modulation and administration of thermosensitizing agents are two methods currently used to increase the extent of direct thermal injury. The processes involved in the progression of thermal injury and therapies that may potentially modulate them remain poorly understood.

CONCLUSION

Focal hyperthermia for the treatment of liver tumors involves complex mechanisms. Evidence suggests that focal hyperthermia produces both direct and indirect tissue injury by differing underlying processes. Methods to enhance the effects of treatment to achieve complete tumor destruction should focus on manipulating these processes.

Effectivity of laser-induced thermotherapy: In vivo comparison of arterial microembolization and complete hepatic inflow occlusion

BACKGROUND AND OBJECTIVES

Laser-induced thermotherapy (LITT) is a promising method for local treatment of liver metastases. The aim of this study was to compare the effect of LITT on lesion size when combined with hepatic arterial microembolization or complete hepatic blood flow occlusion.

STUDY DESIGN/MATERIALS AND METHODS

In a porcine liver model, LITT (30 W 15 minutes) was performed with either normal (n = 12), partially interrupted (arterial microembolization via a hepatic artery catheter n = 12) or completely interrupted hepatic perfusion (Pringle's maneuver, n = 12). LITT lesions were macro- and microscopically assessed after liver dissection.

RESULTS

Hepatic inflow occlusion led to a fourfold increase in lesion volume after arterial microembolization and a ninefold increase after complete interruption (6.3. cm3 vs. 27.1 cm3 vs. 58.8 cm3, P < 0.01).

CONCLUSIONS

Interrupting hepatic perfusion significantly increases lesion volumes in LITT. This beneficial effect can also be achieved in the percutaneous application mode by LITT combined with arterial microembolization via a hepatic artery catheter.

MR imaging–guided breast ablative therapy

The integration of imaging and thermal therapy can provide a minimally invasive or even noninvasive alternative to breast surgery for small tumors. Ongoing trials seek to show safety and efficacy for laser, radiofrequency, microwave, cryoablation, and focused ultrasound surgery. To be successful, these therapies must achieve equivalent or even greater efficacy as surgical outcomes and must demonstrate total ablation of the dominant lesion with negative margins, while sparing normal tissue beyond the target tissue. Procedures have been validated by histopathology subsequent to resection.

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.

Interstitial laser hyperthermia for colorectal liver metastases: the effect of thermal sensitization and the use of a cylindrical diffuser tip on tumor necrosis

OBJECTIVE

Our aim in this study was to investigate the characteristics of a diffuser-tipped optical fiber in producing tumor necrosis, compared to a standard bare-tipped fiber. The potential synergistic effect between thermal sensitization by metronidazole and interstitial laser hyperthermia (ILH)-induced tumor necrosis is also evaluated.

BACKGROUND DATA

ILH is a minimally invasive technique for the treatment of colorectal liver metastases. One of the major limitations is the size of tissue necrosis achieved by a single optical fiber. Use of cylindrical diffuser-tipped fibers and thermal sensitization of tumor cells by metronidazole may increase the size of tumor necrosis achieved by a single optical fiber.

MATERIALS AND METHODS

A model of colorectal cancer liver metastases in male inbred CBA mice was used. Laser hyperthermia was applied to tumor tissue using either a bare optical quartz fiber or a cylindrical diffuser-tipped fiber from a Medilas fibertom 4100 Nd:YAG surgical laser generator. Six hundred joules of energy was applied at two power settings, 5 and 10 watts, using bare- and diffuser-tipped fibers, respectively. The extent of necrosis was assessed by histological techniques. A similar study with three experimental groups was treated with 300 J of applied energy. Extent of immediate tumor necrosis was compared to that seen 24 h after ILH treatment. The third group, which had been treated with intraperitoneal metronidazole prior to ILH, was also assessed for tumor necrosis after 24 h and results compared with both the previous groups.

RESULTS

ILH delivered using a cylindrical diffuser-tipped fiber resulted in a significantly larger diameter of tumor necrosis when compared to a bare-tipped fiber, for a given amount of applied energy. The differences were more significant at higher power settings. Six hundred joules of energy applied by ILH using a bare-tipped fiber at 5 and 10 watts produced 6.7 +/- 1.1 mm and 5.9 +/- 0.6 mm diameter of tumor necrosis, respectively. At equivalent settings, the diffuser-tipped fiber produced 7.7 +/- 1.0 mm and 8.1 +/- 0.6 mm diameter of tumor necrosis (p = 0.02 and p < 0.001). Using a diffuser-tipped fiber and an applied energy of 300 J delivered at 5 watts power, mean diameter of tumor necrosis immediately after treatment was 6.7 +/- 1.1 mm and after 24 h 7.9 +/- 1.3 mm (p = 0.006). Mean diameter of tumor necrosis 24 h after ILH in animals treated with metronidazole was 8.3 +/- 1.9 mm (p = 0.11).

CONCLUSION

Diffuser-tipped optical fiber appears to significantly increase the diameter of ILH-induced tumor necrosis compared to the bare fiber. In contrast to the bare fiber, it enables the application of laser energy using higher power settings without compromising the diameter of tumor necrosis achieved. In animals treated with metronidazole, a trend towards increased tumor destruction at the tumor-host interface was seen on histolopathology. In addition, a trend towards increased diameter of tumor necrosis was also seen; however, statistical significance was not achieved.

Highly Nd3+-doped Y3Al5O12 crystal fiber tip for laser thermotherapy

Based on phonon relaxation, a 12-at. % neodymium-doped YAG (Y3AlrO12) crystal fiber tip has been developed for photothermal conversion. The near-cylindrical tip, with an average diameter of 0.68 mm and a length of 1.8 mm, is fabricated on a 0.65-mm-thick 220-mm-long pure YAG single-crystal fiber by laser-heated growth. Pumped by an 810-nm wavelength diode laser with a pump power of less than 2 W, the temperatures of the tip reach 725 degrees C in air, 78 degrees C in egg white, and 79 degrees C in porcine liver, with acceptable reproducibilities and thermal response times. The photothermal conversion efficiency of the doped tip is approximately 89%, and the high stability of the tip is also proved. Experimental results show that the doped fiber tip is promising for laser thermotherapy applications.

Laser induced thermotherapy (LITT) of experimental liver metastasis-detection of residual tumors using Gd-DTPA enhanced MRI

BACKGROUND AND OBJECTIVE

The aim of this study was to evaluate the accuracy of Gd-DTPA MRI in the detection of recurrent tumor after laserinduced thermotherapy (LITT) of experimental liver metastases.

STUDY DESIGN/MATERIALS AND METHODS

LITT was performed at different energy levels in VX-2 tumor-bearing rabbits (n = 80). MRI and histology were placed at 0, 24, 96 hours, and 14 days. Signal intensities were calculated of the transition between thermally damaged and undamaged tissue (transition zone = TZ) and of the surrounding tissue (reference zone = RZ).

RESULTS

Tumor recurrence was seen in 47 animals. At 24 hours sensitivity, specificity and accuracy was 92, 100, and 95% in TZ and 23, 100, and 50% in RZ. At 14 days sensitivity, specificity and accuracy was 100, 11, and 60% in TZ and 100, 89, and 95% in RZ.

CONCLUSIONS

Recurrence is best excluded in TZ at 24 hour and in RZ at 14 day with an accuracy up to 95%.

Changes in relative light fluence measured during laser heating: implications for optical monitoring and modelling of interstitial laser photocoagulation

Dynamic changes in internal light fluence were measured during interstitial laser heating of tissue phantoms and ex vivo bovine liver. In albumen phantoms, the results demonstrate an unexpected rise in optical power transmitted approximately I cm away from the source during laser exposure at low power (0.5-1 W), and a decrease at higher powers (1.5-2.5 W) due to coagulation and possibly charring. Similar trends were observed in liver tissue, with a rise in interstitial fluence observed during 0.5 W exposure and a drop in interstitial fluence seen at higher powers (1-1.5 W) due to tissue coagulation. At 1.5 W irradiation an additional, later decrease was also seen which was most likely due to tissue charring. Independent spectrophotometric studies in Naphthol Green dye indicate the rise in fluence observed in the heated albumen phantoms may have been primarily due to light exposure causing photobleaching of the absorbing chromophore. and not due to heat effects. Experiments in liver tissue demonstrated that the observed rise in fluence is dependent on the starting temperature of the tissue. Correlating changes in light fluence with key clinical endpoints/events such as the onset of tissue coagulation or charring may be useful for on-line monitoring and control of laser thermal therapy via interstitial fluence sensors.

Metabolic activity and DNA integrity in human hepatic metastases after interstitial laser coagulation (ILC)

BACKGROUND AND OBJECTIVE

For investigations into interstitial laser coagulation (ILC) of solid tumors, tissue whitening is used as a parameter for the extent of coagulation. This obvious demarcation is associated with global thermal denaturation, but it is not clear whether this finding is a good indicator of the exact outer boundary of the lethal tissue effect.

STUDY DESIGN/MATERIALS AND METHODS

ILC with portal inflow occlusion was performed in human hepatic metastases of colorectal carcinoma directly after surgical resection (n = 5) or before surgical resection (n = 5) with laser parameters adapted to tumor diameter. Mitochondrial NADH-diaphorase activity and DNA integrity were assessed by histoenzymatic staining.

RESULTS

In 7 of 10 tumors (mean diameter, 3.7 cm), an area of macroscopic coagulation (mean diameter, 4.2 cm) encircled the tumor in all three axes. Macroscopic coagulation corresponded to absent metabolism and disintegrated DNA. Furthermore, the macroscopic volumes of coagulation produced in tumor were comparable to the dimensions in normal porcine liver with the same laser parameters.

CONCLUSION

ILC with portal inflow occlusion results in areas with complete cell avitality in the zone of tissue whitening in human hepatic liver metastases.

Hepatocellular Carcinoma: Long-term Results of Combined Treatment with Laser Thermal Ablation and Transcatheter Arterial Chemoembolization

PURPOSE

To determine the potential long-term effectiveness of laser thermal ablation (LTA) followed by transcatheter arterial chemoembolization (TACE) in the percutaneous ablation of large hepatocellular carcinoma (HCC).

MATERIALS AND METHODS

Thirty large HCCs 3.5-9.6 cm in diameter (mean diameter, 5.2 cm) and 15 small HCCs 0.8-3.0 cm (mean diameter, 1.9 cm) were treated with ultrasonographically guided LTA with TACE and with LTA alone, respectively, in 30 patients: 19 with a solitary large HCC, and 11 with one to three additional synchronous small HCCS: A 1.064-microm neodymium yttrium-aluminium-garnet (Nd-YAG) laser at a power of 5.0 W was coupled with one to four quartz optic fibers that were advanced through 21-gauge needles. Segmental TACE was performed 30-90 days after LTA. All lesions were evaluated for change in size at computed tomography (CT), alpha-fetoprotein (AFP) levels, recurrence rates, and cumulative survival rates.

RESULTS

No major complications occurred in 127 LTA sessions. CT showed complete tumor necrosis in 27 (90%) of 30 large HCCS: Twenty-eight patients were followed up for 6-41 months (mean, 17.1 months). In 25 patients, all lesions appeared stable or smaller at CT. AFP levels decreased to the normal range in all patients with high pretreatment values. The 1-, 2-, and 3-year local recurrence rate was 7% in large HCCS: Complete tumor necrosis was achieved in all 15 (100%) small HCCs; none of them recurred locally. The 1-, 2-, and 3-year cumulative survival rates were 92%, 68%, and 40%, respectively.

CONCLUSION

LTA followed by TACE is an effective palliative therapy in treating large HCCS:

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.

Thyroid tissue: US-guided percutaneous interstitial laser ablation-a feasibility study

PURPOSE

To evaluate percutaneous interstitial laser photocoagulation (ILP) as a palliative treatment of recurrent thyroid carcinoma untreatable with surgery or radioiodine administration.

MATERIALS AND METHODS

By using 18 resected thyroid glands, the volume and histologic pattern of ILP-induced thyroid damage were assessed. In vivo treatment feasibility was evaluated by using a low-energy laser in two volunteers before thyroidectomy for huge autonomously functioning nodules. With ultrasonographic (US) monitoring, a 21-gauge spinal needle was inserted into the thyroid nodules. A 300-microm quartz fiberoptic guide was inserted through the needle lumen, and the fiber tip was placed in direct contact with the tissue. Laser irradiation was performed with a 1.064-nm Nd:YAG laser in surgically resected glands, which were treated with 2, 3, 5, or 7 W.

RESULTS

Tissue ablation was well-defined histologically, and its area was related to laser irradiation parameters (range, 0-26 mm). No correlation was found between US images and the actual extent of laser-induced lesions. Large colloid or fluid collections did not permit regular heat diffusion within the tissue. In vivo low-energy ILP was performed without technical difficulties or complications.

CONCLUSION

ILP induces well-defined tissue ablation correlated with energy parameters in thyroid glands devoid of cystic areas. ILP could be a therapeutic tool for highly selected problems in thyroid tumor treatment.

Histopathological features of liver damage induced by laser ablation in rabbits

BACKGROUND AND OBJECTIVE

Possible mechanisms that promote or interfere with the effects of laser ablation of the liver have not been clarified. The aim of this study was to define the chronological alterations in the normal rabbit liver at early stages after laser ablation.

STUDY DESIGN/MATERIALS AND METHODS

Rabbit livers were ablated with a laser via an optical fiber and then analyzed histopathologically by immunostaining for heat shock protein 70 (HSP70) and by the terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling (TUNEL) method.

RESULTS

The lesions increased in size progressively over the 24 h that followed ablation and the area of the lesion coincided with the area that had been heated above 43 degrees C. TUNEL-positive hepatocytes were surrounded, at some distance, by HSP70-positive hepatocytes were surrounded, at some distance, by HSP70-positive hepatocytes at 6 h, and such cells were in contact with each other at 24 h.

CONCLUSIONS

Injury to hepatocytes induced by laser ablation increases for 24 h and dying cells express nuclear HSP70, with subsequent fragmentation of DNA.

Interstitial laser coagulation: evaluation of the effect of normal liver blood perfusion and the application mode on lesion size

BACKGROUND AND OBJECTIVE

The effect of temporarily interrupted hepatic blood flow and multiple-fiber application on necrosis volume in interstitial laser coagulation (ILC) was investigated.

STUDY DESIGN/MATERIALS AND METHODS

Single- and multiple-fiber ILC were performed in porcine livers with normal as well as interrupted perfusion. Temperatures were determined. Lesions were measured and studied by light microscopy 4 hours post-treatment.

RESULTS

ILC with multiple-fiber application led to significantly greater individual lesion volumes (3.7 +/- 0.5 cm3) than single-fiber application (2.5 +/- 0.5 cm3) (P < .01). The interruption of hepatic perfusion led to a significant increase in lesion volume with single- (7.5 +/- 1.0 cm3) as well as multiple-fiber application (12.6 +/- 2.2 cm3) (P < .01). Superposition of the lesions in the multiple-fiber application mode was only determined with interrupted perfusion (total volume: 50.3 +/- 6.6 cm3).

CONCLUSION

Interruption of hepatic perfusion increases lesion volumes significantly. ILC for treating liver tumors should preferably be performed by application routes that permit temporary interruption of hepatic perfusion.

Interstitial laser-induced thermotherapy: influence of carbonization on lesion size

BACKGROUND AND OBJECTIVE

The size of laser-induced coagulated lesions produced in porcine muscle in vitro using a cylindrical diffusing fiber tip and a conductive heat source, made by covering the diffuser with a hollow steel needle, were compared to investigate the influence of charring.

MATERIALS AND METHODS

Light from a Nd:YAG laser was utilized for thermotherapy. A theoretical model for calculating tissue temperature was used to predict the experimental results and to simulate in vivo treatments.

RESULTS

The metal-covered tip produced carbonization and tissue vaporization that was not found with the diffuser. After 20 min of irradiation at a laser power of 7 W, the coagulated volumes with and without carbonization were found to be 13.1 cm3 (range 12.4-14.1 cm3, n = 4) and 12.2 cm3 (range 11.5-13.4 cm3, n = 4), respectively. Mathematical simulations showed that in unperfused tissue, a diffusing laser heat source produces smaller lesions than does a conductive heat source at the same power, the difference in coagulated volume becoming smaller with increased treatment time and increased power.

CONCLUSION

Using cylindrical diffusers, interstitial laser-induced thermotherapy without carbonization at the fiber tip can be as efficient as treatment with carbonization.

Thermo-controlled device for inducing deep coagulation in the liver with the Nd:YAG laser

BACKGROUND AND OBJECTIVE

To increase the effectiveness of laser-induced interstitial thermotherapy (LITT), a new thermo-controlled application system for minimal invasive intervention was designed. Our system consists of a laser applicator of 2.5 mm in diameter, insertion equipment, and a Nd:YAG-laser source.

STUDY DESIGN/MATERIALS AND METHODS

A cylindrical light emitting fiber (1-6 cm in length) was placed in the center of the applicator. The surrounding tissue was irradiated through a Duran window at the distal end of the applicator. The power of the laser source was controlled dynamically by thermosensors in a water-cooling system of the laser applicator. The temperature at the surface of the Duran window was kept constant at approximately 60 degrees C, without charring the surrounding tissue.

RESULTS/CONCLUSION

We obtained homogeneous coagulation zones. In in vitro experiments with pig livers, we reached ellipsoid coagulation volumes of 3 and 5 cm in diameter within 10 minutes, corresponding to a volume of approximately 25 cm3.

Heat-resistant cylindrical diffuser for interstitial laser coagulation: comparison with the bare-tip fiber in a porcine liver model

BACKGROUND AND OBJECTIVE

Interstitial laser coagulation is an experimental treatment to eliminate solid tumors such as hepatic metastases. The pattern of light emission from the fiber tip is probably an important factor in determining the size and shape of a lesion. A heat-resistant cylindrical light diffusing tip of 2 cm length was developed for this application. We performed an in vitro study to compare this diffusing-tip with a bare-tip fiber.

STUDY DESIGN/MATERIALS AND METHODS

Fiber ends were positioned between two porcine liver slabs (37 degrees C) and Nd:YAG laser light (1064 nm) was guided through either fiber with an output of 3-9 W and exposure times of 6-18 minutes.

RESULTS

Lesions produced by the cylindrical diffuser tip were significantly larger and more predictable. With the diffuser tip, lesions up to 36/23 mm (length/width) could be produced at 7 W and 9 min without any central charring. The maximum size of lesions produced with the bare-tip fiber was 32/20 mm at 6 W for 9 min with massive charring.

CONCLUSIONS

The results indicate that at optimal laser settings, the diffuser tip produces a larger coagulation volume than a bare-tip fiber. For clinical application, cylindrical diffusing fibers should be used with a diffusing length adapted to the diameter of the tumor.

Dynamic modeling of interstitial laser photocoagulation: implications for lesion formation in liver in vivo

BACKGROUND AND OBJECTIVE

Interstitial Laser Photocoagulation (ILP) is a minimally invasive cancer treatment technique, whereby optical energy from implanted optical fibers is used to therapeutically heat small, solid tumors. In this work, the potential of ILP without tissue charring is investigated.

STUDY DESIGN/MATERIALS AND METHODS

Optical diffusion and bio-heat transfer equations were used to develop dynamic models of interstitial laser heating in liver in vivo. Modifications in the optical properties due to tissue coagulation (T > or = 60 degrees C) were incorporated into the physical description. In addition, the effect of three different blood perfusion patterns on temperature distributions was explored. Model-predicted temperatures were used as an index for thermal damage based on an accumulated temperature injury (Arrhenius) model. Thermal damage dimensions were determined with tissue temperatures constrained to remain below 100 degrees C, so as to minimize the potential for tissue charring and smoke production.

RESULTS

The model predicts that increases in scattering due to coagulation and choice of perfusion pattern affect substantially thermal damage dimensions. The results indicate that, for single fiber ILP at 2.55 W for 600 s, the maximum achievable thermal damage diameter in liver, without charring, is 9.6 mm. In addition, ILP performed with high-low power ramping may have an advantage over constant power treatments, in that, larger volumes of thermal damage can be realized earlier in an irradiation.

CONCLUSIONS

For ILP performed with a single spherical emitting fiber, optimal irradiation parameters exist such that thermal lesions in liver up to approximately 10 mm in diameter can be induced while the maximum tissue temperature remains below 100 degrees C, avoiding tissue charring.

Results of electrochemical therapy of colorectal liver metastases in rats followed up by MRI

RATIONALE AND OBJECTIVES

Direct-current or electrochemical therapy is an alternative method for local tumor therapy. Until recently, it was mainly applied in China and was relatively unknown in the Western world. This study examines the feasibility and effectiveness of applying direct-current therapy in liver metastases of colorectal carcinomas in an animal model.

METHODS

Liver metastases were implanted in 47 BDIX rats by subcapsular injection of cells from a colorectal strain (DHD/K12). The success rate of implantation and the size of the tumors were determined after 3 weeks by MR imaging (T2-weighted turbo spin-echo images; relaxation time 1,800 ms, echo time 80 ms). The direct-current therapy was applied by one platinum electrode placed in the center of the tumor and four at the periphery of the tumor. Suitable therapy parameters were established in a pilot study by comparing four different methods of direct-current therapy with a control group. The methods varied with respect to the electrode polarity and the applied voltage. In a second series of investigations, tumor growth was monitored by MR imaging 3 and 5 weeks after therapy.

RESULTS

The tumor implantation rate was 92.6% at a tumor cell concentration of 8 x 10(5)/mL. The most effective therapy method was achieved by placing an anode at the center of the tumor and four cathodes at the periphery, with an applied charge of 80 C/cm3. Complete tumor necrosis was observed in 54% of cases. In the follow-up measurements, the mean tumor diameter was 0.65 cm at 3 weeks after therapy and 0.76 cm at 5 weeks after therapy. In comparison with the control group (1.08 and 1.53 cm, respectively), this represented a significant reduction in tumor growth rate.

CONCLUSIONS

This study is the first to demonstrate an antitumoral effect of direct-current therapy on liver metastases of colorectal cancer in rats.

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.

Long-term effects of interstitial laser coagulation in porcine liver with portal inflow occlusion: central versus peripheral lesions

PURPOSE

Interstitial laser coagulation (ILC) is an attractive modality for local destruction of unresectable hepatic metastases. Portal inflow occlusion considerably increases its destructive capacity, resulting in lesions 5 cm in diameter; however, effects on adjoining major intrahepatic structures are unknown. Therefore, the purpose of this study was to assess the effects of ILC with portal inflow occlusion on the central portion of the liver as compared to the peripheral portions.

MATERIALS AND METHODS

ILC was performed in pigs with portal inflow occlusion. Each animal received a single laser application with Nd:YAG light guided simultaneously through four interstitial fibers with 5 W per fiber during 6 minutes. Location of treatment was randomized to either central (n = 8) or peripheral (n = 8). Follow-up was for 1, 2, or 3 months with evaluation of liver functions and weight, as well as macroscopic and microscopic assessment of coagulated lesions and surrounding parenchyma.

RESULTS

There was no treatment-related morbidity or mortality. No obstructive cholestasis or bile leakage was found. At every moment of evaluation, coagulated volumes in the central group were smaller than in the peripheral lesions (P = .03). Large vessels contiguous to the lesions in the central group were always intact and indications of portal hypertension or thrombosis of hepatic veins were not found. There were no significant differences between the two groups (liver functions [P > or = .15] and weight [P = .69]).

CONCLUSION

ILC with portal inflow occlusion is a safe technique in the vicinity of vital structures in the liver of healthy pigs. These results justify studies to the feasibility and complication rate of portal inflow occlusion in patients with hepatic malignancies.

Slow intramural heating with diffused laser light: A unique method for deep myocardial coagulation

BACKGROUND

Catheter ablation of postinfarction ventricular tachycardia (VT) may be limited by insufficient myocardial coagulation or excessive endocardial or epicardial damage. We propose that volumetric heating restricted to intramural sites may improve the outcome and safety of this procedure, especially if delivered at rates that enhance heat conduction and forestall adverse tissue changes.

METHODS AND RESULTS

A novel optical fiber with a diffusing tip for direct intramural, volumetric laser heating was tested via thoracotomy and percutaneously in normal dogs. Low-power (2.0- to 4.5-W) diode laser light (805 nm) diffused within tissue induced large lesions but no visible surface damage, mural thrombi, or transmural perforation. Mean lesion depth approximated tip length (10 mm). Mean lesion widths in the thoracotomy and percutaneous groups were 5.8+/-0.5 to 9.1+/-0.84 mm and 5.2+/-0.85 to 7.9+/-1.1 mm, respectively, depending on the light dose. Mean volumes in the percutaneous group were 1006+/-245 to 2471+/-934 mm. ST-segment depression, appearing in unfiltered bipolar electrograms recorded from the guiding catheter, was specific for lesion induction. All dogs survived the protocol, which included a 1-hour observation period. In cross section, lesions were elliptical to spherical and characterized by extensive contraction-band necrosis abruptly bordering viable tissue. No platelets or fibrin adhered to the endocardium.

CONCLUSIONS

Slow, volumetric, and direct intramyocardial heating induces large, deep lesions without hazardous tissue damage. Such heating might cure postinfarction VT more successfully and safely than present techniques. Further testing and development of this method seem warranted.

Interstitial laser coagulation for hepatic tumours

BACKGROUND

The potential role of interstitial laser coagulation (ILC) for patients with irresectable hepatic tumours is currently being investigated. Since its introduction in 1983 it has evolved into an innovative minimally invasive technique.

METHODS

On the basis of a Medline literature search and the authors' experience, the principles, current state and prospects of ILC for hepatic tumours are reviewed.

RESULTS

Animal studies and early clinical studies have shown the safety and feasibility of ILC. The site of interest can be approached at laparoscopy or percutaneously and treatment is easily repeatable. Recent advances include the use of fibres with a cylindrical diffusing light-emitting tip, the length of which is adaptable to tumour diameter, water-cooled fibre systems, simultaneous multiple fibre application, and hepatic inflow occlusion during laser treatment. ILC allows complete destruction of tumours up to 5 cm in diameter. Currently a limitation is the lack of reliable real-time monitoring of laser-induced effects but progress in magnetic resonance imaging techniques should allow accurate temperature measurements to be obtained rapidly during treatment. However, the actual benefit of ILC in terms of patient survival remains to be investigated.

CONCLUSION

In terms of tools and experience, ILC has now been developed sufficiently to study its effect on survival of patients with irresectable hepatic tumours.

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.

Hepatic inflow occlusion increases the efficacy of interstitial laser-induced thermotherapy in rat

Interstitial laser-induced thermotherapy (ILT) destroys tumors thermally. ILT was performed for treatment of liver tumors in rats to investigate the effect of hepatic inflow occlusion on temperature distribution and lesion size. Tumors were irradiated for 20 min with near-infrared light from a neodymium:yttrium-aluminum-garnet (Nd:YAG) laser. The laser light at a power of 1.5 W was delivered through a plane-cut optical fiber, the tip of which was placed in the tumor. Rats in group I received ILT without interruption of hepatic blood flow. Those in group II received ILT during hepatic inflow occlusion. Liver temperatures were measured during treatment. After 3 days the animals were sacrificed and the size of the lesions was measured. Occlusion of the hepatic inflow during ILT increased the maximum lesion diameter, as measured at the liver surface, by 47%. Linear interpolation between the temperatures measured at 6 and 12 mm distance from the fiber tip revealed that the temperature at the necrotic border just before the end of treatment was approximately 45 degrees C in both the occluded and nonoccluded groups, indicating that the hepatic inflow occlusion caused no increase in tissue thermal sensitivity. This study shows that occlusion of the hepatic inflow during interstitial laser-induced thermotherapy causes a significant increase in lesion size, which could have implications for the treatment of hepatic tumors.

High-intensity focused ultrasound in the treatment of experimental liver tumour

This project aimed to determine the adequacy and accuracy of high-intensity focused ultrasound (HIFU) for ablating experimental liver tumour, and to assess imaging methods for monitoring the therapeutic results. The rabbit liver pseudotumour model was established by injection of Freund's complete adjuvant into the liver; the animals then received HIFU therapy via laparotomy at the focal point of the beam (1.1 MHz, 500 W/cm2, 20 s). The rabbits were sacrificed at scheduled times after treatment and liver tumours were examined histologically. Sequential imaging of the liver tumour was performed before and after HIFU treatment. HIFU accurately destroyed the rabbit liver tumour and induced coagulation necrosis 24 h later. Sonographic imaging studies revealed that characteristic changes occurred. A hyperechoic mass turned to a hypoechoic lesion with no Doppler signal, and a high echogenic rim appeared 24 h after HIFU treatment, correlating well with the pathological changes of a sonoablated lesion. These results verify that HIFU has the power to ablate liver tumour quite adequately and accurately, and that sonography is useful for monitoring sonoablated liver tumour.

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.

High-intensity focused ultrasound in the treatment of experimental liver tumour

This project aimed to determine the adequacy and accuracy of high-intensity focused ultrasound (HIFU) for ablating experimental liver tumour, and to assess imaging methods for monitoring the therapeutic results. The rabbit liver pseudotumour model was established by injection of Freund's complete adjuvant into the liver; the animals then received HIFU therapy via laparotomy at the focal point of the beam (1.1 MHz, 500 W/cm2, 20 s). The rabbits were sacrificed at scheduled times after treatment and liver tumours were examined histologically. Sequential imaging of the liver tumour was performed before and after HIFU treatment. HIFU accurately destroyed the rabbit liver tumour and induced coagulation necrosis 24 h later. Sonographic imaging studies revealed that characteristic changes occurred. A hyperechoic mass turned to a hypoechoic lesion with no Doppler signal, and a high echogenic rim appeared 24 h after HIFU treatment, correlating well with the pathological changes of a sonoablated lesion. These results verify that HIFU has the power to ablate liver tumour quite adequately and accurately, and that sonography is useful for monitoring sonoablated liver tumour.

MRI-guided laser interstitial thermal therapy (LITT) of head and neck tumors: progress with a new method

A less invasive method for treatment of tumors is being tested based on interstitial photothermal ablation via infrared Nd:YAG laser fiber optics. The technique can be applied safely and effectively for therapy of common tumors in humans. In the current study five patients were treated by interstitial laser palliation with the Nd:YAG laser using special fiberoptic applicator tips, which distribute laser energy efficiently throughout the tumor volume. Magnetic resonance imaging (MRI) scanning was employed to locate the tumor, position the fibers correctly, and monitor the development of thermal necrosis in the tumors. Two patients were diagnosed with adenoid cystic carcinoma of the paranasal sinuses, one with a recurrent carcinoma of the tongue and oropharynx, one with a recurrent carcinoma limited to the oropharynx, and one patient with a carcinoma of the epi- and oropharynx. The maximum follow-up without recurrence was 2 years in a patient with an adenoid cystic carcinoma tumor of the paranasal sinuses. There were no immediate or delayed complications. Anatomical structures including eyes, brain, and important vessels were recognized by MRI during laser therapy. MRI-guided interstitial laser photothermal ablation appears to be a safe and effective method for treatment of selected tumors of the head and neck region with particular applications in palliation of inoperable tumor recurrences.

Laser surgery in gynecologic oncology

In the treatment of premalignant epithelial cancers of the female lower genital tract, the CO2 laser beam is used with precision through a surgical microscope for tissue ablation and excision. Intra-abdominal vaporization of abnormal tissues can be performed endoscopically through fiberoptics. Surgical lasers provide thermal scalpels for hemostatic excision of malignant lesions. Photodynamic therapy is applied in the treatment of isolated malignancies persistent after conservative treatment. Surgical laser systems are important tools in the treatment of gynecologic malignancies.