Value of kV imaging versus CBCT
Marjolein van Os
Lies Joosten
Erasmus MC – Daniel den Hoed
Rotterdam
Outline
▪ Introduction
▪ Verification
* Prostate patients
* Breast patients
▪ Conclusion
Elekta
kV
MV
CBCT
introduction
prostate
breast
conclusion
Why kV ?
▪ Advantage:
* Lower dosis of kV
* CBCT takes about 2 minutes
kV 0.15 cGy
CBCT 0.5 cGy
* Use smaller margins
▪ Disadvantage:
* kV results in less information than using CBCT
introduction
prostate
breast
conclusion
Position verification procedure
Positioning verification first fraction.
Correction protocols used:
• No Action Level (NAL) protocol:
Imaging first 3 fractions > correction > fraction 4 check
• Extended No Action Level (eNAL)protocol:
Imaging first 3 fractions > correction > fraction 4 check + weekly
imaging (and correcting)
• Online Protocol:
Daily imaging > if necessary a correction > start irradiation
introduction
prostate
breast
conclusion
Imaging Sytems
kV imaging > XVI
Megavolt imaging
> Theraview
Theraview System
Theraview : Specific adjustments
▪ Connection with XVI to import kV image
▪ Automatic 3D marker match
▪ TCSA = ‘Theraview Couch Setup Assistant’
TCSA : ▪ Table activation (in treatment room)
▪ Any shift is performed automatically (in treatment room and control room )
▪ Table can be controlled remotely (online) (in control room)
introduction
prostate
breast
conclusion
Stereograhic targeting (SGT) procedure - 5 fields IMRT
Prostate treatment
MV
3
introduction
prostate
kV
6
SGT = daily prostate positioning
using kV/MV imaging and
implanted gold markers
Goal of SGT:
Optimal prostate positioning for each
fraction (3D)
breast
conclusion
Stereo Graphic Targeting (SGT)
Imaging of Stereo Graphic Targeting:
•
Lateral beam > kV beam
•
AP beam > MV beam
6 MU part of treatment plan
introduction
prostate
breast
conclusion
Set-up prostate patient
Patient setup:
* Head & arm support
* Knee roll
* Feet support
* AP and lateral tattoos
TCSA is activated
A correctional table shift is done
automatically
introduction
prostate
breast
conclusion
Werkwijze SGT
kV beam
Werkwijze SGT
MV beam
Procedure SGT
Daily analysis
Import kV image
Automatic match of the markers
Visual verification
introduction
prostate
breast
conclusion
breast
conclusion
Procedure SGT
Correction
Action level 2 mm
Remote control couch motion
introduction
prostate
iSGT-procedure - 7 fields IMRT
Intra-fractional lateral verification: MV
1
5
4
6
3
7
2
iSGT beam 3
iSGT lateral beam
▪ SGT procedure
▪ Automatic match of the markers
▪ Deviation > 4mm = correction using TCSA
introduction
prostate
breast
conclusion
Smaller margins
100
Directly after SGT
Directly after SGT
After treatment with iSGT
After treatment with iSGT
Cumulative frequency (%)
Frequency (%)
80
After treatment without iSGT
After treatment without iSGT
Time-average with iSGT
60
Time-average with iSGT
Margin reduced from
10 mm to 5 mm
40
20
0
0
2
4
6
8
10
2D sagital plane residue
errors pererror
fraction
(mm)
2D Residual
(mm)
introduction
prostate
breast
conclusion
Breast
whole breast
boost
SIB: simultaneously integrated boost
introduction
prostate
breast
conclusion
Set-up breast patient
Breastboard
Both arms above the head
..
introduction
Kneefix
AP and lateral tattoos
prostate
breast
conclusion
Verification breast
Imaging with kV and MV
kV for verification tumor bed (clips) + eNAL protocol
MV for verification whole breast
MV
kV
introduction
prostate
breast
conclusion
Verification kV images – left breast (3D)
kV
MV
kV
MV
introduction
prostate
breast
conclusion
Clip migration – verification CBCT
Pink
Clip in reference CT position
Green Clip in CBCT position => decreased distance
Clip migration
Clip distance decreased
New CT
Boost volume reduction
introduction
prostate
breast
conclusion
New CT + new plan
Positioning accurate
introduction
prostate
breast
conclusion
prostate
breast
conclusion
Clip migration
introduction
Clip migration
introduction
prostate
breast
conclusion
prostate
breast
conclusion
Check correction
introduction
Grafic eNAL breast patients
Margin reduced
from 8 to 5 mm
introduction
prostate
breast
conclusion
Conclusion
Conclusion:
You can verify the positioning of breast- and prostate patients with
only kV and MV images without using CBCT.
The verification allows us to use smaller margins.
The treatment time is shorter without CBCT.
The radiation dose due to imaging is lower compared to CBCT.
The role of the technicians is important:
They have to keep overview and are responsible for the treatment.
Are there any questions?