IGRT is a radiation therapy process that uses imaging to ensure accurate patient positioning and alignment. Frequent imaging during treatment, such as with CBCT, allows corrections to be made for set-up errors and organ motion. This improves the precision of radiation delivery to the target volume while reducing doses to healthy tissues, leading to better treatment outcomes and fewer side effects.

1. IMAGE - GUIDED RADIATION THERAPY
( IGRT )
Asst.Prof. Surat VINIJSORN
Div. Of Radiation Oncology
Faculty of Medicine Siriraj Hospital
Mahidol University

3. Local control
Identification of the target Delivery of radiation
Excellent dose distribution Precision targeting
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4. Rationale for IGRT
IGRT is a component of the radiation therapy process
that incorporate imaging coordinates from the
treatment plan to be delivered in order to ensure the
patient is properly aligned in the treatment room.

5. Goal and Clinical benefit
 To improve the accuracy of the radiation
field placement
 To reduce the exposure of healthy tissue
during radiation treatment

6. History of “guidance”for treatment
 Surface and skin marks
 Portal imaging ( PORT FILM )
 Electronic portal imaging ( EPID )

7. Imaging for treatment verification
1980’s  Port film
1990’s  Emergence of MV portal imagers
 In-room ultrasound localization
 Marker-based localization
 Fluoroscopic tracking
2000’s  Flat panel imaging (EPID)
 KV digital imaging
 CT – on rail
 KV-CBCT
 MV-CBCT

8. IGRT
Allows us to correct for :
• Set up errors
• Inter-fraction organ motion : Inaccurate set up
because of organ changes in each fraction
• Intra-fraction motion : Organ motion during
treatment

9. IGRT
Indication
 Moving target
 Positioning
 Tumor shrinkage or expansion
 Changes in shape of the tumor and
surrounding anatomy
Jaffray et al.1999

10. IGRT
Adaptive Gating
 Set up errors  Intra-fraction motion
 Inter-fraction organ
motion

11. IGRT
Two-dimensional (2D) IGRT would include :
 matching planar kilovoltage (kV) radiographs
fluoroscopy
 CBCT with two orthogonal images
 megavoltage (MV) images with digital
reconstructed radiographs (DRRs) from the plan
ning CT.

12. IGRT
Three-dimensional (3D) IGRT would
include :
 localization of a cone-beam computed
tomography (CBCT)
 data set with the planning
 computed tomography (CT) data set from
planning

13. Adaptive radiotherapy
 A full implementation of image guided will lead to
the concept of adaptive radiotherapy ( ART )
 In ART the dose delivery for subsequent treatment
fraction of the course of radiotherapy can be
modified to compensate for inaccuracies dose
delivery that can not be corrected simply by
adjusting the patient positioning like in the IGRT

14. Adaptive radiotherapy ( cont.)
The courses of inaccuracies may include :
 Tumor shrinkage during the course of
treatment
 Patient loss weight during the course of
treatment
 Increase hypoxia during the course of
treatment

15. Dynamic Adaptive RT (DART)
• Most exciting use of IGRT is the ability to adapt
treatment to changes in the patient and/or tumor patient
• Although many tumors shrink over the course of
treatment, it is common to largely ignore these changes
and use a single treatment plan
• At best, patients are re-planned once midway through
treatment if large changes occur

16. Adaptive Radiotherapy
The clinical benefit for the patient is
the ability to monitor and adapt to
changes that may occur during the
course of radiation treatment

17. Respiratory Gating

18. Respiratory Gating
NEEDS :
 4D-CT ( Planning CT )
 Virtual Simulation Software
 Motion tracking device
 TPS
 Linac + Gating option

19. IGRT TEAM :
 Oncologist : review image fusion
 Physicist : performs CT & analysis
 RTT : handle patient care

20. IGRT
Summary :
 the process of frequent two and three-
dimensional imaging, during a course of radiati
on treatment, used to direct radiation therapy u
tilizing the imaging coordinates of the actual ra
diation treatment plan
 The patient is localized in the treatment room in
the same position as planned from the
reference imaging dataset.

21. Summary
The verify of image :
 4D-CT ( planning CT )
 PET-CT
 SPEC
 ULTRASOUND
 MRI
 CBCT

22. Summary
CBCT
Support :
 Patient set up
 Disease targeting
 Adaptive treatment planning

23. Summary
Image matching
 Planning CT.: bony match
 CBCT : bony and soft tissue match
( 2D and 3D match )

24. Summary
Imaging for treatment guidance :
 Fluoroscopy
 Computed tomography conventional
 Cone beam CT ( KV,MV )
 Optical tracking

25. IGRT Process
 Dicom data from the CT reports voxel in the
patient coordinate system
 Normalize for patient orientation to achieve “CT
coordinate system”
 Affine transformation matrix can then convert to
room coordinate system
 Finally, knowledge of the linac isocenter
coordinate and table axis of rotation allows
shift vector and rotation table calculated
 Move the treatment couch by press one button
 Treatment

26. Correction strategies for patient
positioning during IGRT
 On-line
 Off-line