Thulium laser-assisted endoscopic third ventriculostomy: Determining safe laser settings using in vitro model and 2 year follow-up results in 106 patients

Safeness and efficacy of 2-µm handheld thulium laser during microsurgical resection of supratentorial and infratentorial meningiomas: Experience of a single center

Aims

We performed a retrospective nonrandomized study to analyze the results of a microsurgery of intracranial meningiomas using 2-μm thulium flexible handheld laser fiber (Revolix jr).

Methods

From February 2014 to December 2021, 75 nonconsecutive patients suffering from intracranial meningiomas, admitted in our department, have been operated on with microsurgical technique assisted by 2-μm thulium flexible handheld laser. We have reviewed demographic and clinical data to evaluate safety and efficacy of the technique.

Results

There were no complications related to the use of the 2-μm thulium laser. We operated on a high percentage of cranial base and tentorial and posterior fossa meningioma in our series. The neurological outcome and degree of resection did not differ from previous series. The neurosurgical team found the laser easy to use and practical for avoiding bleeding and traction.

Conclusion

The use of 2-μm thulium fiber handheld flexible laser in microsurgery of intracranial meningiomas seems to be safe and to facilitate tumor resection, especially in "difficult" conditions (e.g., deep seated, highly vascularized, and hard tumors). Even if in this limited retrospective trial the good functional outcome following conventional microsurgery had not further improved, nor the surgical time was reduced by laser, focusing its use on "difficult" (large and vascularized) cases may lead to different results in the future.

Safety of a Novel Thulium Fiber Laser for Lithotripsy: An In Vitro Study on the Thermal Effect and Its Impact Factor

Introduction: To investigate the thermal effect on the water by a novel thulium fiber laser (TFL) designed for lithotripsy and evaluate the safety of this laser for clinical use. Materials and Methods: An in vitro experimental setup was constructed. A test tube filled with saline was immersed in an electric water bath, and a TFL fiber and a thermal probe were inserted into it. Saline was irrigated into the tube and pumped out synchronously at the same speed by two pumps, respectively, to maintain convection when needed. Then, continuous TFL firing of different power settings was imposed to saline in the tube for 60 seconds, on the conditions of different irrigation rates. The temperature was recorded every 5 seconds during the whole trial, and each trial was repeated five times. Safety threshold of temperature increase (STTI) was determined comparing with the deemed safe temperature of 43°C in vivo. Results: On condition of 0 mL/min irrigation rate, STTI was 6.5°C, and water temperature increase (WTI) caused by ≥15 W settings surpassed STTI after 20 seconds of laser firing; on condition of 15 mL/min irrigation rate, only WTI caused by the highest 30 W power setting surpassed STTI after 45 seconds of laser firing. When irrigation rate was added up to 25 and 50 mL/min, WTIs caused by all power settings were below STTIs in a 60-second experiment. High frequency and low pulse energy combinations caused a slightly higher WTI compared with low frequency and high pulse energy, given a constant power and irrigation rate. Conclusion: Power setting and irrigation rate collaboratively play a critical role in WTI during TFL lithotripsy, and it is safe to use TFL referring to the thermal effect as long as there is moderate irrigation, while TFL power should be lowered enough when irrigation is ceased.

The Comparison of Thermal Effects of a 1940-nm Tm:fiber Laser and 980-nm Diode Laser on Cortical Tissue: Stereotaxic Laser Brain Surgery

BACKGROUND AND OBJECTIVES

The thermal damage on adjacent healthy structures is always an unwanted consequence of continuous-wave laser irradiation of soft tissues. To propose a laser as an effective alternative to traditional surgical tools, this photothermal damage due to heat conduction must be taken into account with a detailed laser dosimetry study. Two candidate lasers; a 980-nm diode and 1940-nm Tm:fiber were selected for this study. Despite the poor absorption by water, the 980-nm diode laser has been one of the most widely used lasers in soft tissue surgeries due its good absorption by hemoglobin, which provides good homeostasis. The second laser; the Tm:fiber laser was selected due to its wavelength operating at an absorption peak of water (1,940 nm), which makes it a good candidate for ablation of biological tissues, and it is readily capable of being transmitted through flexible fiber optics to deliver energy to hard-to-reach regions. The underlying motivation for the research described in this paper is that with a comprehensive comparison of ablation capabilities and a detailed dose study of infrared lasers operating at different wavelengths and temperature monitoring of the tissue during laser surgery, it may be possible to specify the optimal laser parameters for laser surgery, and propose a treatment alternative to conventional surgical techniques in clinical use. The objectives of this study were to investigate and to compare the thermal effects of 980-nm and 1940-nm lasers on cortical tissue in vivo, to find the optimum parameters for laser-brain-ablation with minimum thermal damage to the surrounding healthy tissue, and finally, to analyze laser irradiated tissue thermographically and histologically to correlate thermal events and tissue damage with laser irradiation parameters.

STUDY DESIGN/MATERIALS AND METHODS

Stereotaxic laser brain surgeries were performed on 32 male Wistar rats. A t-type thermocouple was used to measure the temperature of the nearby tissue at a distance of 1 mm above and 1 mm away from the fiber tip during laser surgery. Cresyl fast violet (CFV) staining was used to expose the thermal extent of laser surgery on cortical tissue. Eight tissue samples from each laser study group were processed for histological analysis and the mean ± standard deviation for thermal damage was reported. Thermal damage was quantified as ablation (thermally removed tissue), severe and mild coagulation (irreversible thermal damage) and edematous (reversible thermal damage) areas with regard to CFV stained slices. The Pearson correlation coefficient was calculated to test if the ablation efficiencies and total damage, and edematous areas were correlated to rates of temperature change.

RESULTS

No significant adverse effects were observed during surgeries. We found that both lasers investigated were successful in cortical tissue removal. Our results also revealed that irrespective of the mode of operation, laser wavelength and laser power, there is a strong correlation between the rates of temperature change and ablation efficiencies and a negative correlation between the rate of temperature change and total damage and edematous area.

CONCLUSIONS

Both lasers investigated were successful in cortical tissue removal. We also reported that when the amount of energy delivered to the tissue was constant, the most important issue was to deliver this energy in a short time to achieve more efficient ablations with less edema around the lesion, regardless of mode of delivery (continuous or pulsed-modulated mode), but further studies including the healing period after laser surgeries have to be performed to compare the thermal extent of damage comprehensively. Lasers Surg. Med. © 2019 Wiley Periodicals, Inc.