Stereotactic Radiosurgery (SRS)

Stereotactic Radiosurgery (SRS) is a highly precise form of radiation therapy used to treat tumors and other abnormalities, primarily in the brain and spine, but also in other parts of the body. Despite the name "radiosurgery," it is a non-surgical procedure that does not involve incisions. Instead, it delivers intensely focused beams of radiation to a specific target area, minimizing exposure to surrounding healthy tissues.

How Stereotactic Radiosurgery Works

SRS utilizes advanced imaging and planning software to deliver a high dose of radiation to a precisely defined target in one or a few treatment sessions. The process involves:

Detailed Imaging: High-resolution imaging techniques such as Magnetic Resonance Imaging (MRI), Computed Tomography (CT), and sometimes angiography are used to create a detailed three-dimensional map of the tumor or target area.

Treatment Planning: A multidisciplinary team, typically including a neurosurgeon, radiation oncologist, and medical physicist, uses specialized computer software to develop a customized treatment plan. This plan determines the optimal number, shape, and intensity of radiation beams, as well as the angles from which they will be delivered to converge precisely on the target.

Immobilization: To ensure the patient remains perfectly still during treatment, a method of immobilization is used. For treatments in the head, this often involves a rigid frame attached to the skull or a custom-molded mask. For body treatments, vacuum molds or other devices may be used.

Radiation Delivery: Using a specialized machine (such as a Gamma Knife or a linear accelerator-based system like CyberKnife), multiple radiation beams are directed at the target from different angles. Individually, these beams are low-intensity as they pass through healthy tissue. However, at the point where they intersect at the tumor, they deliver a very high, concentrated dose of radiation.

The high dose of radiation damages the DNA of the tumor cells, inhibiting their ability to grow and reproduce. Over time, this can cause the tumor to shrink or stop growing.

Stereotactic Radiosurgery for Acoustic Neuromas

Acoustic neuromas, also known as vestibular schwannomas, are benign tumors that grow on the nerve connecting the brain to the inner ear (the vestibulocochlear nerve). SRS is a common and effective treatment option for acoustic neuromas, particularly for:

• Small to medium-sized tumors: SRS can be effective at controlling the growth of these tumors.
• Patients who are not surgical candidates: This may be due to age, underlying health conditions, or the location of the tumor making traditional surgery risky.
• Tumors that have residual growth or recur after surgery.

The primary goals of SRS for acoustic neuromas are to halt or slow tumor growth and to preserve the function of the hearing and facial nerves. While SRS does not remove the tumor, it can effectively control its size and prevent further damage to surrounding structures.

Stereotactic Radiosurgery for Other Tumors

SRS is also used to treat a variety of other tumors and conditions in the brain and other parts of the body, including:

• Meningiomas: Benign tumors arising from the membranes covering the brain and spinal cord. SRS can be an option for smaller meningiomas, especially those in difficult or sensitive locations.
• Ependymomas: Tumors that originate from the lining of the brain's ventricles and the spinal cord's central canal. SRS may be used for ependymomas that cannot be completely removed surgically or that recur.
• Other Schwannomas: Benign tumors that can develop on nerves throughout the body.
• Brain Metastases: Cancers that have spread to the brain from other primary cancer sites. SRS is often used to treat a limited number of brain metastases.
• Certain Gliomas: Some types of primary brain tumors.
• Arteriovenous Malformations (AVMs): Abnormal tangles of blood vessels.
• Trigeminal Neuralgia: A painful nerve condition.

For these conditions, SRS aims to control the growth of the tumor or lesion, alleviate symptoms caused by compression or irritation of surrounding tissues, and preserve neurological function.

The Stereotactic Radiosurgery Procedure

The SRS procedure is typically performed on an outpatient basis and involves several steps:

1. Preparation: This includes the necessary imaging scans and the fitting of the immobilization device.
2. Treatment Planning: The medical team finalizes the precise radiation delivery plan.
3. Treatment: The patient is positioned on the treatment couch, and the immobilization device is secured. The SRS machine then delivers the radiation beams according to the plan. The patient is monitored throughout the procedure, which can take anywhere from 30 minutes to several hours.
4. Recovery: After the treatment, the immobilization device is removed. Patients are typically observed for a short period before being discharged to go home.

Potential Benefits and Risks

Benefits:

• Minimally Invasive: No surgical incision or general anesthesia is typically required.
• High Accuracy: Precise targeting minimizes radiation exposure to healthy tissues.
• Convenience: Often completed in a single treatment session.
• Lower Risk: Generally associated with fewer risks and a faster recovery compared to traditional surgery.

Risks and Side Effects:

Potential side effects are usually temporary and depend on the area being treated. They can include:

• Headache, nausea, or dizziness.
• Fatigue.
• Swelling in the treated area.
• Temporary hair loss (for head treatments).
• Skin irritation at the pin sites (if a head frame is used).
• In rare cases, more significant neurological side effects can occur depending on the location and size of the treated area.

The decision to use SRS is made on an individual basis after a thorough evaluation by a multidisciplinary team, considering the specific type, size, and location of the tumor, as well as the patient's overall health and treatment goals.

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