In neurosurgery practice, the use of radiosurgery techniques in the treatment of a wide variety of brain lesions is increasingly becoming widespread. Radiosurgery is an important alternative to surgery in many intracranial lesions. Rapidly developing technology has also paved the way for the development of radiosurgery systems, and thus the indications for use have expanded considerably. Radiosurgery is sometimes an alternative to surgery and a complementary to surgery at another times, and is the only treatment option in many places. As in other radiotherapy techniques, the aim here is to provide the best tumor control and to cause the least side effects. Radiosurgery allows external treatment of the brain and other neural tissues, with the use of minimally invasive methods at the forefront. Gamma Knife radiosurgery, Cyberknife Radiosurgery, Linear Accelerator Based Systems, Proton and Heavy Load Particle Treatment, Hypofractionated Stereotactic Radiotherapy are the systems used for this purpose.

Radiosurgery is an important alternative treatment method to surgery in many intracranial lesions. It has been in a continuous development since the first time it was revealed and started to be applied. Today, where minimally invasive approaches are preferred, stereotactic radiosurgery has a great place and efficiency. It was first described by the Swedish scientist and neurosurgeon Lars Leksell in 1951, and the first patients were treated in 1967. Although it was previously designed as a non-invasive treatment option for functional diseases, later developments resulted in a wide variety of brain tumors such as benign malignant tumors and arteriovenous malformations. It has also been used in the treatment of lesions. As a result of the rapid progress of technology, radiosurgery systems have also developed in parallel and have become acceptable are the world by being applied in many indications

In stereotaxic radiosurgery, beams from many different angles are directed to the target volume determined stereotactically, while high doses are reached in the overlap area of the beams, rapid dose reduction occurs in normal tissues other than the target lesion.

As in other radiotherapy techniques, the aim here is to provide the best tumor control and to cause the least side effects. Gamma knife radiosurgery, Cyberknife radiosurgery, Linear Accelerator-based systems, proton and heavily loaded particle therapy, hypofractionated stereotactic radiotherapy are the systems used for this purpose.

Radiosurgery is currently used in a wide range of diseases; schwannoma, arteriovenous malformation, meningioma, pituitary adenoma, chordoma, brain metastases, glial masses, trigeminal neuralgia, movement disorders and more to be found.

Cyberknife Radiosurgery is an ablative treatment method that combines the technique of using many beams from a high-energy radiation source based on the stereotactic localization principle.

The term radiosurgery is generally used for stereotactic radiotherapy (SRT) applied in a single fraction. Cyberknife (Accuray, Sunnyvale, CA, USA) is a new frameless robotic radiosurgery system developed for stereotactic radiotherapy applications. Adler et al from Standford University, who worked with Leksell. They first described this robot-centered system in an article they published in 1995. In this system, which is defined as image-guided radiosurgery, the tumor is targeted with frameless immobilization. The system, which performs 3D reconstruction of the skull thanks to previously obtained CT, coordinates the data obtained from the radiographs with these images. Six

MV linear accelerators and a very light radiation source are integrated into this system and move on 6 different coordinate axes on the robot.

In the 1990s, Accuray company combined the features of this system and introduced it as Cyberknife and started to use it in intracranial and spinal cases. It received FDA approval in 2001, paving the way for its use in all body treatments. Cyberknife radiosurgery system consists of a patient bed and a linear accelerator that produces 6 MV X-rays placed on a robot.

Robot sensitivity is very high. Unlike other methods, Cyberknife combines a computer-controlled robot system conjunctively to another computer-controlled robot system to detect the location of the target with imaging during the procedure and provide the irradiation of tumors with high sensitivity.

As in other radiosurgery methods, this system does not have a cap placed under local anesthesia and a thermoplastic mask is used instead.

This is a condition that patients tolerate more easily and therefore its use in cases requiring multiple fractions provides an important advantage in this respect. There are hardware and software parts of the system. Hardware parts include linear accelerator, robotic manipulator, x-ray imaging system, stereo camera system; software components include 6D skull tracking, x-sight spine tracking, x-sight lung tracking, fiducial marker tracking, adaptive image acquisition systems, synchrony respiratory tracking system. It Generates 6MV X-rays using a linear accelerator magnetron, stable wave, and accelerator; dose rate is 1000cGy/min. The linear accelerator is located on the robotic manipulator. In the Cyberknife radiosurgery system, image-guided treatment is performed with 2 diagnostic X-ray sources mounted in the room, and real-time tumor tracking can be performed during treatment thanks to image recording algorithms.

Thanks to the algorithms for image identification, target determination, dose calculation, optimization, and optimizing treatment efficiency, a comprehensive treatment planning system emerges and increases treatment success.

Linear Accelerator-Based Systems In stereotactic radiosurgery, is aimed to create a surgical effect by destroying benign and malignant tumor cells by necrosis or apoptosis by giving radiation to a well-defined target.

Betti and Colombo developed the first linear accelerant (LINAC) based radiosurgery system in 1983 with special apparatus placed in the gantry. Winston and Lutz developed the stereotactic frame in 1986, which has a three-dimensional coordinate system suitable for the LINAC-based system.

In the last 20 years, with the development of new generation LINAC systems with enhanced imaging and fiber properties, stereotactic radiosurgery application to the whole body has become possible

Radiosurgery is applied with different devices. Although there are technical differences between the devices, there is no significant difference in treatment results.

The use of LINAK-based systems, which can be used for extracranial irradiation and fractionated treatment, is less costly and easily accessible. Novalis, X-knife, Tomotherapy are some of the LINAC-based radiosurgery systems on the market.

X-rays shaped with collimators are directed to the target previously determined stereotactically. The LINAC gantry rotates around the patient and the patient table moves in the horizontal plane, resulting in multiple non-coplanar beams. While these beams intersect at the target volume to form

a dense dose zone, the non-target intersection of the co-dose curves is minimized and the surrounding normal brain tissue is to ensure that the minimum dose is received.

Immobilization can also be done with a thermoplastic mask system instead of a stereotactic frame. In treatment planning; The first step of planning for the patient who comes with an intracranial tumor is to make a thermoplastic mask for the patient, and CT and MRI images are obtained. These images are then combined in the system. Sensitive structures in the target volume and its surroundings are contoured and isodose curves are created by using calculation systems to give the desired dose to the target volume. The treatment dose is usually adjusted according to the 70-90% isodose curve, and the treatment plan and isodose distributions are evaluated on CT scans. After the quality control tests are done and the treatment area is checked, the patient’s treatment starts. The images from the planning device are compared with the images taken before and during the treatment, and after the necessary corrections, the tumor is irradiated with high accuracy.

Today, when minimally invasive approaches are preferred, stereotactic radiosurgery has a great place and efficiency. As a result of the rapid advancement of technology, radiosurgery systems have also developed in parallel. It has started to be applied in many indications and has become acceptable around the world.