Medical application: Detailed explanation of the principle and application prospect of laser interstitial hyperthermia

The treatment of brain tumors has evolved with the development of modern science and technology. The appearance of CT/MRI makes the diagnosis of brain tumors more accurate. The surgical navigation system makes the intraoperative tumor location more perfect. Gamma knife/stereotactic radiotherapy is a brain tumor patient. Created a new treatment model. However, to date, there are still no satisfactory treatments for patients with brain tumors with deep location, small size, adjacent brain functional areas, and poor general condition.

Cerebral interstitial hyperthermia has been used clinically for decades, but it has not been widely used in neurosurgery due to the lack of non-invasive temperature monitoring mechanism and accurate and effective heating methods. In recent years, with the development of optical fiber bundles and the modification of lasers, the application of lasers in neurosurgery has been more convenient.

Principle of laser interstitial hyperthermia

Radiofrequency, microwave, magnetic field (in the middle of the tumor in the middle of the tumor), freezing can cause brain tumor tissue necrosis through temperature changes, but it inevitably leads to brain tissue damage around a large area of ​​tumor necrotic tissue. A krypton-bismuth-aluminum-garnet laser (ND-YAG) or a carbon dioxide laser is often used in the clinic. MRI temperature imaging enables real-time temperature monitoring. Animal experiments have shown that if the laser optical fiber is placed in the brain tissue, the laser is converted into thermal energy in the target region, which in turn leads to tissue coagulation, necrosis, and degeneration and atrophy. The volume of laser interstitial hyperthermia depends not only on the laser energy, but also on the light/thermal characteristics of the target tissue. There is only a narrow (<1 mm) transition zone between the central necrosis of the target area and the surrounding normal brain tissue. Necrotic tissue caused by laser hyperthermia can be gradually absorbed within a few months.

The effect of interstitial laser is directly related to temperature. No permanent damage is caused below 43°C; thermal damage caused by 44～59°C depends on the action time of laser; higher than 60°C can cause immediate protein denaturation, tissue coagulation necrosis; At 100 ° C, the cell membrane is broken and the tissue is vaporized, resulting in a so-called "popcorn effect." It is very dangerous to use ultra-high temperature without adequately exposing the tumor to the craniotomy. The temperature of the interstitial laser hyperthermia should be controlled between 50 and 70 °C.

Laser interstitial hyperthermia surgery skills

The first step of the procedure is to place the laser fiber in the middle of the tumor using a framed or frameless stereotactic approach. The procedure can be performed under general anesthesia or local anesthesia, then the fiber is fixed on the skull and the patient is placed. Transfer from the operating room to the nuclear magnetic chamber. MRI verifies the position of the laser fiber and then laser hyperthermia (Figure 1).

During the treatment, the patient remained awake and the whole treatment of the hyperthermia was performed under MRI immediate temperature imaging (Fig. 2). MRI can also provide imaging of hyperthermia after treatment (Figure 3).

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