CT simulation is an important part of the radiotherapy planning process. It allows for 3D visualization of patient anatomy using CT scans. Various immobilization devices are used to accurately position the patient for treatment planning and delivery. The summary describes the key steps in CT simulation including patient setup using immobilization devices, obtaining CT images with appropriate parameters, and noting important details in the patient record for their specific diagnosis and treatment area. CT simulation provides critical 3D information to optimize radiotherapy treatment planning.

1. IMPORTANCE OF
CT- SIMULATION IN
RADIOTHERAPY

2. WHAT IS SIMULATION ?
• A simulation is an approximate imitation of the operation of a process or system
that represents its operation over time.
SIMULATOR
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SIMULATION PROCESS

3. SIMULATION TYPE IN
RADIOTHERAPY
2D 3D 4D

4. 2D / CONVENTIONAL SIMULATION
 Radiotherapy field determination unit using X-ray machine.
 The Geometrical,Mechanical and Optical properties are same as actual
teletherapy unit.
 Consists of following parts :
1) Gantry.
2) Simulator head.
3) X-ray generator.
4) Imager/ detector.
5) Couch

5. 2D / CONVENTIONAL SIMULATION
ADVANTAGE DISADVANTAGE
 Cheapest among rest
 Less radiation exposure than CT
 Fast and Efficient
 Generate verification radiograph
 No limitation in patient positioning.
 Planning limited to only 2D
method.
Difficult to visualize anatomy.
Radiation exposure.

6. 3D / CT SIMULATION
The CT scanner is used to acquire a volumetric CT-Scan of a
patients which represents the “virtual” replica of patient.
CT-SIM COMPONANTS
1) Flat Couch,
2) Laser system(with external laser) ,
3) X-ray tube,
4) X-ray Detectors,
5) Large Bore aperture (80cm-GE Light speed Xtra)
6) Larger Field of View (65cm-GE Light speed Xtra)
7) Collimators and attenuator,
8) Display monitor and work station,
9) Control Console.

7. 3D / CT SIMULATION PROCEDURE
SETUP IMMOBILIZATION IMAGING

8. SETUP PROCEDURE IN
CT SIMULATION
DIAGNOSIS
AREA OF INTEREST
FOR IMAGING
SUITABLE SETUP FOR
TREATMENT

9. SETUP PROCEDURE IN
CT SIMULATION
THORAX SETUP
HEAD AND NECK
SETUP
BREAST SETUP
PELVIC REGION
SETUP
MOTION MANAGEMENT
SPECIFIC SETUP
MODIFIED/CUSTOM
SETUP

10. IMMOBILIZATION IN
CT SIMULATION
“Immobilization are said to be the most crucial parts
of radiation therapy treatment.”
Why we need Immobilization?
To position target accurately.
To minimize the dose to surrounding normal tissue as far as possible.
Reduces the time in daily patient setup .
Makes the patient feel more secure and less apprehensive.
Reduces the reliance on patient cooperation and alertness..

11. IMMOBILIZATION DEVICES
A. Thermoplastic cast ( 3 Pts./5 Pts.)
B. Index Bar.
C. All in One Base plate (AIO)
D. Foam wedge ( 0°,5°,10° and 15° Cushion wedge)
E. Lateral Support (0° and 5°)
F. Head Rest(Supine) Low Density ( With lateral neck Flap : A-1/B-3/C-5 ,
With out Lateral Neck Flap : A-2/B-4/C-5 and “U” Pillow)
G. Head Rest (Prone)
H. Low Density Positioning Blocks ( 20 mm and 40 mm)
I. Low Density Positioning Wedge (9° and 18° )
J. Arm Support / Rest (Low and High)
K. Hand Grip pole and Holder.
L. Knee Rest / Knee support.
M. Leg separator.
N. Base plate extension

12. VISUAL OVERVIEW OF SOME
IMMOBILIZATION DEVICE
Thermoplastic cast:
Head – 3 Point Head,Neck and Shoulders – 5 point
Index Bar/Locating Bar:

13. VISUAL OVERVIEW OF SOME
IMMOBILIZATION DEVICE
All In One Base plate:

14. VISUAL OVERVIEW OF SOME
IMMOBILIZATION DEVICE
Foam Wedge:
0° Wedge
Thorax and
Abdomen
5° Wedge
Thorax and
Abdomen
10° Wedge
Thorax and
Abdomen
15° Wedge
Thorax and
Abdomen

15. VISUAL OVERVIEW OF SOME
IMMOBILIZATION DEVICE
Arm Rest:
Low Arm Rest High Arm Rest

16. VISUAL OVERVIEW OF SOME
IMMOBILIZATION DEVICE
Lateral supports:
Lateral support 0° Lateral support 5° Lateral support 10° Lateral support 15°

17. VISUAL OVERVIEW OF SOME
IMMOBILIZATION DEVICE

18. VISUAL OVERVIEW OF SOME
IMMOBILIZATION DEVICE
Head Rest(Supine) Low Density With Lateral Neck Support :
Head Rest(Supine) Low Density Without Lateral Neck Support :

19. VISUAL OVERVIEW OF SOME
IMMOBILIZATION DEVICE
Head Rest(Prone)

20. VISUAL OVERVIEW OF SOME
IMMOBILIZATION DEVICE
Low Density Positioning Blocks:
20 mm 40 mm
Low Density Positioning Wedge:
9° 18°

21. VISUAL OVERVIEW OF SOME
IMMOBILIZATION DEVICE
Knee rest:
Base Plate Extension:

22. VISUAL OVERVIEW OF SOME
IMMOBILIZATION DEVICE
Vac Lock:

23. IMAGING IN CT-SIMULATION
Why we use CT image for Radiotherapy Planning?
a. The CT images excellent soft tissue contrast allowing for greatly
improved tumor localization and defining in comparison to
conventional simulator.
b. Patient contour may be obtained easily from CT data in particular
the patients skin contains target and any organs of interest.
c. The target volume and its position are identified with relative case of
each CT slice.

24. IMAGING IN CT-SIMULATION
Important Parameters for simulation Imaging via CT scan
a) Scan type.
b) Scan Length.
c) Number of Images.
d) Thick speed.
e) Interval.
f) Field of View.
g) Energy(kV).
h) Gun current rate(mA).
i) Scan Protocol.
Parameter inputs are different for different Setups or
point of anatomical site, which we discuss later.

25. IMAGING IN CT-SIMULATION

26. PRACTICAL OVERVIEW OF
SETUP,IMMOBILIZATION AN IMAGING
TECHNIQUE IN DIFFERENT DIAGNOSIS.
All parameters are as per my departmental
observation at Tata Medical Center.

27. BRAIN,HEAD AND
NECK SETUP
SUITABLE SETUP,IMMOBILIZATION AND
IMAGINE ACCRODING TO DIAGNOSIS SITE
SETUP MODALITY(FOR SUPINE POSITION):
SETUP SHEET

28. BRAIN,HEAD AND
NECK SETUP
SUITABLE SETUP,IMMOBILIZATION AND
IMAGINE ACCRODING TO DIAGNOSIS SITE
IMMOBILIZATION MODALITY
 For brain 3 point/for Head,Neck and shoulder 5 point.
 Suitable Head rest according to patient comfort.
 Wedge and Blocks under head rest according to patient comfort.
 Index bar.
 AIO board
 Cushion extension.
IMAGING MODALITY
After taking coronal and sagittal scout.
Scan Length : as per instruction.
Slice Thickness : 2.5 mm ( WEBRT/PALL – 5 mm)
Interval : same as slice thickness.
Gun current(mA) : Auto

29. BRAIN,HEAD AND
NECK SETUP
SUITABLE SETUP,IMMOBILIZATION AND
IMAGINE ACCRODING TO DIAGNOSIS SITE
IV CONTRAST MODALITY (If Doctor Prescribe)
SITE CONTRAST DOSE MAXIMUM DOSE INJECTION RATE DELAY TIME
Brain 1.5 ml/kg 80 ml 1.2 ml/sec 60 sec
Head and Neck 2 ml / kg 100 ml 1.5 ml/sec 60 sec
Depends upon Creatinine Clearance.
IMPORTANT POINTS TO NOTE ON RECORD
1. Table to Isocenter distance.
2. CSD
3. No. of points in mould.
4. Head rest/wedge/Block.
5. Date.
6. Other specific instruction.
7. CT Isocenter Marking on Cast or Body.
TI

30. SUITABLE SETUP,IMMOBILIZATION AND
IMAGINE ACCRODING TO DIAGNOSIS SITE
SETUP MODALITY(FOR SUPINE POSITION):
SETUP SHEET
PELVIC REGION
SETUP

31. PELVIC REGION
SETUP
SUITABLE SETUP,IMMOBILIZATION AND
IMAGINE ACCRODING TO DIAGNOSIS SITE
IMMOBILIZATION MODALITY
Index bar.
 AIO board
 Cushion extension.
 0° Foam wedge cushion.
 leg separator/knee rest/knee support/lateral knee support.
IMAGING MODALITY
After taking coronal and sagittal scout.
Scan Length : as per instruction.
Slice Thickness : Standard – 2.5 mm / palliative – 5 mm
Interval : same as slice thickness.
Gun current(mA) : Auto

32. PELVIC REGION
SETUP
SUITABLE SETUP,IMMOBILIZATION AND
IMAGINE ACCRODING TO DIAGNOSIS SITE
IV CONTRAST MODALITY (If Doctor Prescribe)
Depends upon Creatinine Clearance.
IMPORTANT POINTS TO NOTE ON RECORD
1. Table to Isocenter distance.
2. Knee distance.
3. Knee rest,leg separator position.
4. Lateral knee support position.
5. Date.
6. CT Iso center Marking on Cast or Body(Patient specific tattoo) .
7. Other specific instruction.
SITE CONTRAST DOSE MAXIMUM DOSE INJECTION RATE DELAY TIME
ABDOMEN 2 ml/kg 100 ml 1.7 ml/sec 60 sec
PANCREAS 2 ml/kg 100 ml 2.5 ml/sec 40 sec
PELVIS 2 ml/kg 100 ml 1.7 ml/sec 80 sec

33. SUITABLE SETUP,IMMOBILIZATION AND
IMAGINE ACCRODING TO DIAGNOSIS SITE
SETUP MODALITY(FOR SUPINE POSITION):
SETUP SHEET
THORAX SETUP

34. THOEAX SETUP
SUITABLE SETUP,IMMOBILIZATION AND
IMAGINE ACCRODING TO DIAGNOSIS SITE
IMMOBILIZATION MODALITY
Index bar.
 AIO board
 Cushion extension.
 Head rest / U Pillow
 0° Foam wedge cushion.
 Arm rest high/low.
Grip holder- Grip pole.
Lateral arm support as per patient comfort.
IMAGING MODALITY
After taking coronal and sagittal scout.
Scan type : For Lung only Helical and Axial (For overview tumor movement)
Scan Length : as per instruction.
Slice Thickness : Standard – 2.5 mm / palliative – 5 mm
Interval : same as slice thickness or modified by system itself.
Gun current(mA) : Auto

35. THORAX SETUP
SUITABLE SETUP,IMMOBILIZATION AND
IMAGINE ACCRODING TO DIAGNOSIS SITE
IV CONTRAST MODALITY (If Doctor Prescribe)
Depends upon Creatinine Clearance.
IMPORTANT POINTS TO NOTE ON RECORD
1. Table to Isocenter distance.
2. CSD
3. Hand grip pole number and position
4. Arm rest type(High or Low)
5. Date.
6. CT Iso center Marking on Cast or Body(Patient specific tattoo)
7. Other specific instruction.
SITE CONTRAST
DOSE
MAXIMUM
DOSE
INJECTION
RATE
DELAY TIME
THORAX 1.5 ml/kg 80 ml 1.5 ml/sec 60 sec

36. SUITABLE SETUP,IMMOBILIZATION AND
IMAGINE ACCRODING TO DIAGNOSIS SITE
SETUP MODALITY(FOR SUPINE POSITION):
SETUP SHEET
BREAST SETUP

37. BREAST SETUP
SUITABLE SETUP,IMMOBILIZATION AND
IMAGINE ACCRODING TO DIAGNOSIS SITE
IMMOBILIZATION MODALITY
Index bar.
 AIO board
 Cushion extension.
 Head rest / U Pillow
 0°/5°/10°/15° Foam wedge cushion.
 Arm rest high/low.
Grip holder- Grip pole.
Lateral arm support as per patient comfort.
IMAGING MODALITY
After taking coronal and sagittal scout.
Scan Length : as per instruction.
Slice Thickness : Standard – 2.5 mm / palliative – 5 mm
Interval : same as slice thickness or modified by system itself.
Gun current(mA) : Auto.

38. BREAST SETUP
SUITABLE SETUP,IMMOBILIZATION AND
IMAGINE ACCRODING TO DIAGNOSIS SITE
IV CONTRAST MODALITY (If Doctor Prescribe)
Depends upon Creatinine Clearance.
IMPORTANT POINTS TO NOTE ON RECORD
1. Table to Isocenter distance.
2. CSD
3. Hand grip pole number and position.
4. Cushion wedge type.
5. Arm rest type(High or Low)
6. Specific bolus,
7. Scar marking with Radiodensity wire marker.
8. Scar position note on record file.
9. Date.
10. CT Iso center Marking on Cast or Body(Patient specific tattoo)
11. Other specific instruction.
Same as thorax protocol.

39. DIBH FOR LEFT
BREAST
DIBH- Deep Inspiration Breath Hold Technique.
Mostly used in Left Breast Irradiation.
1. Using Deep Inspiration to move Heart out of the irradiating field
2. Using RPM to track as an external marker block surrogate for internal
movement.
3. Placing the marker in Xiphisternum midline.
4. Marking(Tattoo) the Free Breath,Breath hold and four corners of the marker.
5. At least 3 Practice sessions.
6. Have to note down distance between BH and FB tattoo.
Free Breath marking Breath Hold marking

40. DIBH FOR LEFT
BREAST
WITHOUT DIBH WITH DIBH

41. SUITABLE SETUP,IMMOBILIZATION AND
IMAGINE ACCRODING TO DIAGNOSIS SITE
SETUP MODALITY(FOR SUPINE POSITION):
MODIFIED/CUSTOM
SETUP
For different type of diagnosis area or sites with different
immobilization and imaging modality.
Example:
Vaclock,Frog Leg,swimers position,Prone setup etc.

42. IMPORTANT POINTS FOR CT-SIM OPARATOR
A. Patient consent confirmation before procedure.
B. Verify Patient Identity.
C. Always follow Oncologist’s instruction.
D. Always aware about patient comfort.
E. Choosing perfect setup as per diagnosis.
F. Using suitable Immobilization device as per patient comfort and treatment site.
G. Before injecting IV Contrast should aware about patient allergic reaction.
H. Post IV Contrast record.
I. Doctor consent confirmation of IV contrast procedure.
J. Using Exact delay time during with contrast scan.
K. Always ready for Emergency situation during IV contrast scan.
L. Choosing right Imaging protocol as per treatment site or Instruction.
M. Choosing right parameter inputs during imaging.
N. Measuring TI and CSD after setup done and note down in patient record file.
O. Note down other inputs in patient record file .
P. Verify ROB position in correct plane.
Q. Verify correct bolus and wire marker position and site.
R. Verify patient scan image via doctor or physicist.
S. Record images in DICOM.

43. THANK YOU
Saikat Roy
Intern – DRT
Department of Radiation Oncology.
Tata Medical Center.