STEREOTACTIC RADIOSURGERY

 STEREOTACTIC RADIOSURGERY (SRS)

  Stereotactic radiosurgery is non-surgical radiation therapy used to treat brain tumours and other brain diseases that cannot be treated with conventional surgery. Stereotactic radiosurgery (SRS) and stereotactic radiation therapy (SRT) are both radiation therapy for tumours. SRS involves a single radiation therapy, but over time, SRT uses a series of treatments. SRS is a high-dose treatment, but SRT is used for radiation therapy in smaller doses in multiple stages of treatment. SRS and SRT are used to kill cancer cells through external radiation sources. When SRS is used to treat tumours in the body, it is called stereotactic body radiation therapy (SBRT). SBRT is used to treat tumours of the lung, liver, abdomen, spine, prostate, head, and neck.

Radiosurgery precisely targets the tumour, so it can shrink the tumour without damaging healthy tissue. It uses 3D imaging to direct high doses of radiation to the affected area and works by destroying the DNA of the target cells. Then the affected cells lose the ability to reproduce, causing the tumour to shrink.

Staged radiosurgery, also called Fractionated stereotactic radiosurgery (FSR), is the process of dividing the total dose of stereotactic radiation into several smaller doses of radiation on different days of treatment. In some cases, compared to single-dose radiosurgery, staged treatment effectively kills the tumour while at the same time appears to reduce potential side effects.

WORKING PRINCIPLE

SRS works in the equal manner as different varieties of radiation treatment. It would not get rid of the tumour however those cells lose their ability to reproduce. Special equipment focuses many small beams of radiation on tumours or other targets. Each beam has almost very little on the tissue it passes through, but the target radiation dose will be delivered at the intersection of all the beams.

 High-dose radiation irradiated to the affected area will cause the tumour to shrink and close the blood vessels over time after treatment, thus depriving the tumours of its blood supply.  In most cases, radiosurgery has a lower risk of side effects compared to other types of traditional surgery or radiotherapy.

EQUIPMENT USED

There are three basic kinds of equipment’s used in stereotactic radiosurgery

• Gamma knife
• Linear accelerator (LINAC)
• Proton beam or heavy charged particle radiosurgery

Gamma knife

Gamma Knife is a type of radiation therapy that uses computerized treatment planning software to help doctors locate and illuminate small targets in the head and brain with very high accuracy. This treatment can deliver strong radiation doses to the target area without affecting the surrounding tissues. It uses multiple beams of radiation that converge in three directions to precisely focus a small volume (such as a tumour), so that large doses of radiation can be delivered to that volume safely.

Linear accelerator (LINAC)

The Medical Linear Accelerator (LINAC) can customize high-energy X-rays or electrons to suit the shape of the tumour and kill cancer cells without affecting the surrounding healthy tissues. It has a variety of built-in safety measures to ensure that you can administer the drug as prescribed, and is regularly checked by medical physicists to ensure that it is working properly.

Proton beam Heavy-charged-particle radiosurgery

Proton therapy delivers radiation to tumour tissue in a more limited way than traditional photon therapy, allows the radiation oncologists to use higher doses and reduce side effects.

BEFORE THE PROCEDURE

Preparation of gamma knife and LINAC stereotactic radiosurgery of the brain is very similar and involves three steps.

Head frame placement

Before the operation begins, patient will have a lightweight frame with four pins attached to their head. This frame will stabilize the head during radiation therapy and will serve as a reference point for focusing the radiation beam. Certain types of brain radiosurgery may not require a helmet.

If patient need a headrest,  they receive anaesthetic injections at four places where pins are inserted into the scalp: two points on the forehead and two points on the back of the head. Patient’s hair will not be shaved, they can get a special shampoo to clean their scalp and help the frame stay in place.

Patient do not need a LINAC stereotactic radiosurgery helmet. Radiosurgery can usually be done with a soft plastic mask attached to the face. The advantage of this method is that it facilitates multiple treatments (three to five) and avoids the discomfort of mounting the frame.

Imaging

After placing the head frame, patient will perform an imaging scan of the brain to show the location of the tumour.

Dose planning

The results of the brain scan are entered into a computerized planning system that allows the radiosurgery team to plan the appropriate area to be treated, the radiation dose, and how to focus the radiation beam to treat that area.

DURING THE PROCEDURE

Children are often anesthetized during imaging tests and radiosurgery. Adults are usually awake, but they can take a mild tranquilizer to help you relax.

By using a gamma knife, patient will lie on the bed that slides into the machine and the head frame will be firmly attached to the bed frame. The machine does not move during the treatment, but the bed moves inside the machine. The process can take less than an hour to about four hours, depends on the size and shape of the affected area . If LINAC stereotactic brain radiosurgery is used, the treatment will be faster.

 Unlike the gamma knife, the LINAC machine moves and rotates around the target during treatment to emit radiation beams from different angles. The treatment lasted less than an hour.

During the procedure:

• Patient won’t feel the radiation
• Patients will able to talk with the doctor through microphone

AFTER THE PROCEDURE

If patient use the head frame, remove it. They may have a small amount of bleeding or tenderness at the pin site.

SIDE EFFECTS OF SRS

• Skin problems
• Fatigue
• Nausea and vomiting
• Difficulty swallowing
• Hair loss in treatment area
• Swelling especially of the brain