This document summarizes the process of simulation for radiation therapy treatment planning from CT imaging to treatment verification. It describes how patient positioning is done using lasers during CT scanning and how the CT images are imported into the treatment planning system. It also explains how the treatment planning system localizes CT markers and defines the isocenter in machine coordinates for treatment. Finally, it summarizes the verification process of aligning the patient using digital reconstructed radiographs and portal images to ensure accurate treatment delivery.

1. CT-to-TPS-to-verification
summary of simulation process
Vibha Chaswal, Ph.D.

2. Know the co-ordinate system TPS
uses
Patient co-ordinate system (not
used in Pinnacle)
CT co-ordinate system

4. 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

5. 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)

6. 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

8. • 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

9. Thank You!

10. Thank You!