CT-to-TPS-to-verification summary of simulation process

Vibha Chaswal, Ph.D.

Know the co-ordinate system TPS uses

Patient co-ordinate system (not used in Pinnacle)

CT co-ordinate system

Image data on acquisition on CT

• Image request form: Patient positioned using lap lasers (ct bb’s on lap lasers)

• Immobilization devices marked• Orientation and technique (protocol) selected

in CT• Topogram acquisition• CT scan acquisition• Dicom images send to TPS and archive

TPS processes• Image data imported• Scanning information verified ( patient position,

orientation)• CT bb’s are localized w.r.t. CT room lasers co-ordinate

system• ROIs are contoured and isocenter is defined w.r.t machine

co-ordinate system• Shifts from ct-bb’s to isocenter are given w.r.t treatment

table (up/down, L/R, in/out)• Segmentation, TP (beams, blocks, dose) and DRRs

generated (set-up and field)• Transfer TP to record and verify (LEX), DRRs to machine

(coherence)

Verification processes• Set patient to CT-bb’s• Get shifts to isocenter from DRR’s, make shifts• Check SSD• Take portal image using field DRRs or Set-up

DRRs (orthogonal and oblique DRRs)• Compare DRR with portal image and verify shift

(orthogonal gives sup-inf and left-right info oblique gives A-P)

• Mark lasers on patient if everything matches, these are treatment isocenter localization marks

• Bite-block – physicist verifies the physical positioning of bite-block before CT scan, radiocam localization no ct bb’s

• Cone-beam – Cone beam field with CT image and segmented structures sent to machine, MVCT image compared with the help of bony land-marks and contours

Thank You!