What is CT simulation?
CT simulation is an imaging and planning session performed before the main course of radiotherapy begins.
Very important: CT simulation is not a treatment radiation session. CT imaging is used to obtain the detailed images needed to design the radiotherapy plan.
The resulting images help the team assess the body's position, the treatment area and its relationship to nearby tissues and organs.
Why is CT simulation necessary?
Radiotherapy is a precise treatment. Planning aims to deliver an appropriate dose to the target while protecting nearby healthy tissues and organs as far as possible.
To achieve this, the care team needs precise information about the patient's anatomy and the treatment area's location.
CT simulation images are a key basis for radiotherapy planning, helping the team determine the patient's position and how treatment will be delivered in later sessions.
How long does CT simulation take?
The time required depends on the treatment area, imaging type, immobilization needs and the center's protocols.
In many cases, patients need approximately 30–60 minutes at the center to complete the various steps of this session.
What happens on CT simulation day?
Understanding the process can help you attend the simulation session with greater peace of mind.
Step 1: Initial preparation
You may be asked to wear a hospital gown or remove certain personal items.
Depending on the treatment area and the doctor's instructions, your bladder may need to be full or empty. Oral or injected contrast may sometimes be used to visualize certain structures more clearly.
Step 2: Positioning
Radiotherapy technicians position you on the machine's couch and adjust your body position.
The chosen position should be one the patient can reproduce as closely as possible at subsequent treatment sessions.
Step 3: Immobilization devices
Special immobilization devices may be used to reduce movement and improve treatment precision.
Conforming cushions
Vacuum cushions can conform to the patient's body and help maintain the required position.
Thermoplastic masks
Special masks may be used in head and neck treatments to keep the head and neck in position.
Please note: These devices are generally used to improve treatment accuracy, and the care team aims to keep the patient as comfortable as possible.
Step 4: The scan
After positioning, the couch moves gently into the CT scanner's opening.
During imaging, stay as still as possible and follow the technician's instructions.
Technicians monitor imaging and stay in contact with you through audio and video systems.
Step 5: Skin marking
Specific points may be marked on the skin to reproduce the body position more accurately in subsequent treatment sessions.
Marks may be made using a medical marker or, in some cases, as a few very small permanent skin dots.
These marks act as Treatment coordinates and guidance and help the care team reproduce the patient's position as accurately as possible between sessions.
What happens after CT simulation?
Patients can usually leave the center after simulation, following the care team's instructions.
A radiation oncologist and medical physicists then review the images and use specialist software to design the patient's treatment plan.
Specialist doctor
examines the target volume and nearby sensitive structures and defines the treatment goals.
Medical physicist
uses treatment planning systems to calculate and evaluate beam delivery and dose distribution.
Final treatment plan
Treatment begins according to the designed plan after it has been reviewed and approved.
Tips for reducing stress
It is natural to feel anxious before your first CT simulation. A few simple tips can make the experience more comfortable.
Get in touch
Tell the technicians if you feel pain or discomfort while lying on the treatment couch.
Stay calm
CT simulation is an imaging and planning stage. Breathe calmly and follow the care team's instructions.
Protect the marks on your skin
If your skin has been marked, avoid scrubbing or washing that area vigorously.
Ask your questions
Ask your doctor or radiotherapy staff if you have questions about imaging, immobilization devices or the next steps.
Important patient questions
Is CT simulation painful?
CT imaging itself is usually painless. Remaining in a fixed position may be uncomfortable for some patients; tell your care team if you feel discomfort.
Will I receive treatment radiation during this session?
No. This stage obtains images for treatment planning and is different from the actual radiotherapy sessions.
When does treatment start after CT?
Planning time depends on the patient's condition and the plan's complexity. Your care team will tell you when treatment sessions will begin.
Important: This article provides general information about CT simulation. Preparation, contrast agents, bladder requirements, immobilization devices and other details may differ according to the treatment area and each patient's plan. Always prioritize your care team's instructions.