Conventional vs CT-SIM

Differences between Conventional and CT simulation

Differences	Conventional simulation	Computed tomography simulation
Treatment position	Identified with to bony landmarks under fluoroscopic condition	Identified to bony landmarks through the use of scout+pilot image
Identification of target volume	Identified from bony landmarks	Can get directly from CT data
Determination of beam geometry	-Verified using fluoroscopic -Doesn’t have standard beam geometry	-Verified from BEV/DRR -Have standard beam geometry
Contour acquisition	Patient contour is obtained through the use of lead wire (manual)	Patient contour is obtained from CT data
Shielding design	-From bony landmarks -Cannot use with beam geometry	-Conformal to target -Can be used together with the beam geometry
Virtual simulation	No	Yes
Image of radiograph	Have limited soft tissue contrast	Have good soft tissue contrast

Machine for Conventional and CT simulator

A conventional treatment simulator

A dedicated radiotherapy CT simulator

SUMMARY OF THE CONVENTIONAL SIMULATION

PROCEDURE FOR A TYPICAL PATIENT (SIX STEPS)

step	Conventional simulation
1	Determination of patient treatment position with fluoroscopy
2	Determination of beam geometry
3	Determination of field limits and isocentre
4	Acquisition of contour
5	Acquisition of BEV and set-up radiographs
6	Marking of patient

SUMMARY OF THE PROCEDURE FOR A TYPICAL

PATIENT COMPUTED TOMOGRAPHY SIMULATION (NINE STEPS)

step	CT simulation
1	Determination of patient treatment position with pilot/scout films
2	Determination and marking of reference isocentre
3	Acquisition of CT data and transfer to virtual simulation workstation
4	Localization and contouring of targets and critical structures
5	Determination of treatment isocentre with respect to target and reference isocentre
6	Determination of beam geometry
7	Determination of field limits and shielding
8	Transfer of CT and beam data to the TPS
9	Acquisition of BEV and set-up DRRs

Images

Pilot or scoutimages relate slice position to radiographic landmarks

A DRR. Note that grey levels, brightness and contrast can be adjusted to

provide an optimal image

A DRR with superimposed BEV for a vertex field of a brain patient. This

treatment geometry would be impossible to simulate on a conventional simulator.

Treatment field in a conventional simulation