What is Stereotactic Radiotherapy?
Radiation therapy (or radiotherapy) is commonly used to treat many types of cancer. It uses high energy X-rays to damage cancer cells, which in turn stops those cells from growing or causes them to die. The aim of radiotherapy is to kill cancer cells whilst causing as little damage as possible to the normal body cells around the cancer.
Stereotactic Radiosurgery (SRS) and Stereotactic Body Radiotherapy (SBRT) are very effective radiotherapy techniques. These treatment techniques enable a high dose of radiation to be delivered to the cancer cells using a precisely focused method whilst sparing the neighbouring normal cells. The main difference between SRS and SBRT treatments and conventional treatment are:
- A higher radiation dose can be delivered to the cancer cells resulting in better cancer outcomes
- The lower radiation dose to the other body cells results in fewer side effects
- SBRT allows the treatment to be delivered in fewer sessions (usually 3-5 sessions over 1-2 weeks)
- Each session will take approximately 30-45 minutes compared to 10-20 minutes
What is the difference between Stereotactic Radiosurgery and Stereotactic Body Radiotherapy?
The difference between SRS and SBRT is the number of sessions involved and the area to which treatment will be delivered.
SRS is used to define treatments that involve one session only and are delivered to areas within the brain.
Treatments to the brain can also be delivered over multiple sessions; this is known as Fractionated Stereotactic Radiotherapy (fSRT).
SBRT uses multiple treatment sessions, usually 3-5, and delivers treatment to areas outside the brain (e.g. pelvis, lung, bone, and spine).
What conditions are suitable for SRS/SBRT?
SRS or fSRT can be used to treat:
- Brain metastases
- Recurrent brain tumours
SBRT can be used to treat small to medium size malignant tumours in the following sites:
- Lung cancer or metastases (spread) to the lung
- Spine metastases
- Bony metastases (non-spine)
- Cancer to the lymph nodes
Stereotactic Simulation, Planning & Treatment Process
Simulation & Planning
SRS/fSRT requires your head to be as still as possible. This immobilisation is achieved by making a head support and a plastic mask. These are made during your CT-simulation appointment.
The mould is made first using a foam product which forms around the head, neck and shoulders – maintaining the position and angular rotation of the head and neck for every SRS/SRT treatment.
The mask is then made using a thermoplastic mesh which is warmed and placed over the face, hardening as it cools. The thermoplastic mask is shaped so as to give the exact impression of your face and head. There are holes in the mask so you can breathe easily.
SBRT also requires the area of your body that is being treated to be as still as possible. Special vacuum cushions are used to maintain your body in a position that is ideal for treatment delivery, this positioning varies depending on the area of the body you are having treated. You may be required to have your arms up above your head, on your chest or by your side. In each case your arms will be supported by the moulded vacuum cushions. In most cases, your knees and feet will be supported by knee and foot position modules.
For SBRT cases, after the completion of the CT scan, you will be given several permanent tattoos (small dots on your skin), which assist us to set you up in exactly the same position for your treatment.
In some cases, such as the treatment of tumours of the lung, compression devices such as an adjustable plate or belt may be used to control breathing motion.
It is important that you are comfortable in your scanning position, as you will have to lie in the same position for the duration of your planning and treatment sessions. If you are not comfortable, please advise the radiation therapist.
Once the mould and thermoplastic mask are made, and/or the vacuum cushions moulded to your body shape, a CT scan of the area you are having treated is performed. If you are having treatment for lung cancer, your breathing is taken into consideration due to its impact on the position of the tumour. During the scanning process you may be given instructions on how to breathe.
Once the session is complete you can go home. The images obtained during this CT scan along with any MRI/PET scans of your tumour are used by specialists to carefully plan your radiotherapy.
After the CT/Planning session you usually have to wait no more than 1-2 weeks for the treatment team to create your treatment plan.
During treatment, you are required to lie down on the treatment table in the same position as you were for your planning CT scan. The radiation therapist will help get you into the correct position and add any moulds or equipment that you may require. Scans are then taken of your position and adjustments are made to achieve sub-millimetre accuracy prior to treatment delivery.
The stereotactic radiotherapy is delivered by a state-of-the-art linear accelerator (LINAC). A LINAC is a device which accurately delivers high energy x-rays to the target area.
Each treatment session can take between 30-60 minutes. The treatment staff are outside the treatment room for the majority of the treatment, and are able to hear and see you the entire time through intercom and closed circuit TV. Once the treatment is completed, you can go home.
Your Radiation Oncologist will review you throughout the treatment course. Radiation Therapists will coordinate all appointments with you.