Radiosurgery is surgery using radiation, that is, the destruction of precisely selected areas of tissue using ionizing radiation rather than excision with a blade. 

It is usually used to treat cancer. 

Involves a single radiation treatment that delivers a highly conformal dose the a target while sparing the surrounding normal tissues.

The addition of a stereotactic boost after whole brain radiation improves the survival of patients with 1 brain metastasis, and improves the performance status of patients with 2-3 metastatic lesions.

May improve local control in patients with multiple brain metastases but it does not improve survival when added to whole brain radiation.

Refers to surgery using radiation to destroy precisely selected areas of tissue using ionizing radiation rather than excision with a blade.

Usually used to treat cancer.

In stereotactic radiosurgery (SRS), the word stereotactic refers to a three-dimensional coordinate system that enables accurate correlation of a virtual target seen in the patient’s diagnostic images with the actual target position in the patient.

Stereotactic, the term refers to a three-dimensional coordinate system that enables accurate correlation of a virtual target seen in the patient’s diagnostic images with the actual target position in the patient. 

Also called stereotactic body radiation therapy (SBRT) or stereotactic ablative radiotherapy (SABR) when used outside the central nervous system (CNS).

Localization accuracy and precision that are of utmost importance for radiosurgical interventions.

Stereotactic accuracy and precision are significantly increased by using a device known as the N-localizer.

The aim of stereotactic radiosurgery is to destroy target tissue while preserving adjacent normal tissue,

Fractionated radiotherapy relies on a different sensitivity of the target and the surrounding normal tissue to the total accumulated radiation dose.

Tumors that are too large or too close to critical organs for safe radiosurgery may be suitable candidates for fractionated radiotherapy.

When used outside the CNS it may be called stereotactic body radiation therapy (SBRT) or stereotactic ablative radiotherapy (SABR).

Radiosurgery is performed by a multidisciplinary team of radiation oncologists and medical physicists to operate and maintain highly sophisticated, highly precise and complex instruments, including medical linear accelerators, the Gamma Knife unit and the Cyberknife unit.

The highly precise irradiation of targets within the brain and spine is planned using information from medical images that are obtained via computed tomography, magnetic resonance imaging, and angiography.

Radiosurgery is indicated primarily for the therapy of tumors, vascular lesions and functional disorders.

General contraindications to radiosurgery include: large size of the target lesion, or lesions too numerous for practical treatment.

Patients treated for one to five days as outpatients.

The radiosurgery outcome may not be evident until months after treatment, and does not remove the tumor but inactivates it biologically.

Lack of growth of the lesion is normally considered to be treatment success.

Indications for radiosurgery include: many kinds of brain tumors, such as acoustic neuromas, germinomas, meningiomas, metastases, trigeminal neuralgia, arteriovenous malformations, and skull base tumors, among others.

Expansion of stereotactic radiotherapy to extracranial lesions is increasing, and includes metastases, liver cancer, lung cancer, pancreatic cancer, etc.

The main principle of radiosurgery is selective ionization of tissue, by means of high-energy beams of radiation.

Ionization is the product of ions and free radicals.

Ions and free radicals are usually deleterious to the cells, and they may be formed from the water in the cell or biological materials, can produce irreparable damage to DNA, proteins, and lipids, resulting in the cell’s death.

The biological inactivation is carried out in the tissue to be treated, with a precise destructive effect.

The radiation dose is usually measured in grays (one gray (Gy) is the absorption of one joule of energy per kilogram of mass).

The sievert is a unit that describes both the amount of energy deposited and the biological effectiveness of radiation and accounts for different organs, and different types of radiation.

The Gamma Knife is used to treat brain tumors by administering high-intensity cobalt radiation therapy in a manner that concentrates the radiation over a small volume.

A Gamma Knife typically contains 201 cobalt-60 sources of approximately 30 curies, each placed in a hemispheric array in a heavily shielded assembly.

The device aims gamma radiation through a target point in the patient’s brain.

The patient wears a specialized helmet that is surgically fixed to the skull, so that the brain tumor remains stationary and an ablative dose of radiation is sent through the tumor in one treatment session

Like all radiosurgery, Gamma Knife uses doses of radiation to kill cancer cells and shrink tumors, delivered precisely to avoid damaging healthy brain tissue.

Gamma Knife is able to accurately focus many beams of gamma radiation on one or more tumors.

Each individual beam is of relatively low intensity, so there is little radiation effect on intervening brain tissue and is concentrated only at the tumor itself.

Gamma Knife radiosurgery efficacious proven for patients with benign or malignant brain tumors up to 4 centimeters in size, vascular malformations such as an arteriovenous malformation (AVM)

In the treatment of trigeminal neuralgia the procedure may be used repeatedly on patients.

Acute complications following treatment are rare,

A linear accelerator produces x-rays from the impact of accelerated electrons striking a high z target (usually tungsten).

A Linac gantry moves in space to change the delivery angle.

Linear accelerator equipment can also move the patient to change the delivery point.

Treatments use stereotactic frames to restrict the patient’s movement.

Some systems use a frameless, non-invasive immobilization technique with X-ray imaging that is comfortable for the patient and accurate.

Non-invasive immobilization devices are coupled with real-time imaging to detect any patient motion during a treatment.

Linear accelerators emit high energy X-rays, ref2242ed to as X-ray therapy or photon therapy.

The term gamma ray is usually reserved for photons that are emitted from a radioisotope such as cobalt-60, and is not substantially different from that emitted by high voltage accelerators.

In linear accelerator therapy, the emission head , the gantry, is mechanically rotated around the patient, in a full or partial circle.

The table where the patient is lying, can also be moved in small linear or angular steps.

The combination of the movements of the gantry and of the couch makes possible the computerized planning of the volume of tissue that is going to be irradiated.

Devices with a high energy of 6 MeV are the most suitable for the treatment of the brain,

Due to the depth of the target, devices with a high energy of 6 MeV are the most suitable for the treatment of the brain,

The diameter of beam leaving the emission head can be adjusted by collimators, and can be moved dynamically during treatment to shape the radiation beam to conform to the mass to be ablated.

Linear accelerators are capable of achieving extremely narrow beam geometries, such as 0.15 to 0.3 mm, and can be used for several kinds of surgeries.

Cyberknife therapy refers to a type of linear accelerator mounted on a moving arm to deliver X-rays to a very small area which can be seen on fluoroscopy.

Cyberknife may be compared to Gamma Knife therapy, but it does not use gamma rays emitted by radioisotopes.

Cyberknife does not use a frame to hold the patient, as a computer monitors the patient’s position during treatment, using fluoroscopy.

The robotic concept of Cyberknife radiosurgery allows the tumor to be tracked, rather than fixing the patient with a stereotaxic frame, and can be extended to treat extracranial tumors.

The Cyberknife robotic arm tracks the tumor motion, so that a combination of stereo x-ray imaging and infrared tracking sensors determines the tumor position in real time.

Protons may also be used in radiosurgery.

There is no evidence that proton therapy is better than any other types of treatment.

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