Clinical implementation of 3D EPID-based
in vivo dose verification of IMRT/VMAT
treatments
Ben Mijnheer
Disclosure
The Netherlands Cancer Institute – Antoni van Leeuwenhoek
Hospital has a research cooperation with Elekta concerning the
development of cone-beam CT and EPID dosimetry software
EPID-based in vivo 3D dose verification
using a back-projection model
1) Calculate plan
2) Measure EPID dose
3) Reconstruct dose in
multiple planes
Patient CT
4) Compare planned and reconstructed 3D dose distribution
Clinical use of 3D EPID-based in vivo dosimetry
Number of EPID dosimetry verified plans per year
6000
4000
non IMRT/VMAT
3000
VMAT
IMRT
2000
1000
20
14
(e
xp
ec
te
d
)
20
13
20
12
20
11
20
10
20
09
0
20
08
number of plans
5000
year
Clinical use of 3D EPID-based in vivo dosimetry
• New software tools were clinically introduced to allow automated
image acquisition, to periodically inspect the record-and-verify
database, and to automatically run the EPID dosimetry software
Clinical use of 3D EPID-based in vivo dosimetry
• New software tools were clinically introduced to allow automated
image acquisition, to periodically inspect the record-and-verify
database, and to automatically run the EPID dosimetry software
• The comparison of the EPIDreconstructed and planned 3D
dose distribution is done offline
and data are available a few
minutes after delivery
• Alerts are immediately raised,
without any human intervention,
when deviations are outside
clinical criteria, and actions
scheduled
Clinical use of 3D EPID-based in vivo dosimetry
• New software tools were clinically introduced to allow automated
image acquisition, to periodically inspect the record-and-verify
database, and to automatically run the EPID dosimetry software
• The comparison of the EPIDreconstructed and planned 3D
dose distribution is done offline
and data are available a few
minutes after delivery
• Alerts are immediately raised,
without any human intervention,
when deviations are outside
clinical criteria, and actions are
scheduled
3D in vivo dose verification of prostate VMAT
g
automatic classification
g-analysis statistics
isoc dose
3D g-evaluation in the volume
enclosed
by the 50% isodose surface(all arcs)
isoc dose
Clinical results of 3D EPID-based in vivo dosimetry
(2012)
82% of the verified plans were within
tolerance level (automatically approved)
Clinical results of 3D EPID-based in vivo dosimetry
(2012)
82% of the verified plans were within
tolerance level (automatically approved)
18% of the verified plans had at least one of
the alert criteria outside tolerance level
(limitation of transit dosimetry,
Breast IMRT: influence of setup error
The problem
The solution: shift the measured images
The cause: 1.6 cm shift
Clinical results of 3D EPID-based in vivo dosimetry
(2012)
82% of the verified plans were within
tolerance level (automatically approved)
18% of the verified plans had at least one of
the alert criteria outside tolerance level
(limitation of transit dosimetry, tumor
regression,
Head–and-neck VMAT: tumor regression
After adding bolus, in vivo dosimetry
showed that the dose was OK
planning CT
cone-beam CT
Clinical results of 3D EPID-based in vivo dosimetry
(2012)
82% of the verified plans were within
tolerance level (automatically approved)
18% of the verified plans had at least one of
the alert criteria outside tolerance level
(limitation of transit dosimetry, tumor
regression, anatomical changes ….)
Lung step & shoot IMRT: recovery from atelectasis
Lung step & shoot IMRT: recovery from atelectasis
Based on the in vivo dosimetry and CBCT results it was
decided to replan te patient
Clinical results of 3D EPID-based in vivo dosimetry
(2012)
82% of the verified plans were within
tolerance level (automatically approved)
18% of the verified plans had at least one of
the alert criteria outside tolerance level
(limitation of transit dosimetry, tumor
regression, anatomical changes ….)
1/300 of the verified plans required
immediate action (errors in the procedure
in the clinic)
Head-and-neck VMAT: bolus not present
during planning CT scan
Head-and-neck VMAT: bolus not present
during planning CT scan
New CT scan and plan: in vivo dosimetry OK!
Breast non-IMRT field: incorrect positioning of jaws
“Something is
wrong with the
first field”
Breast non-IMRT fields: incorrect positioning of jaws
“Something is
wrong with the
first field”
Problem:
A button “asymmetric beam”
was accidentally ticked just
before treatment, resulting in a
symmetric adjustment of the
backup jaws for one beam
Action:
Extra field for the remaining
fractions
Online EPID-based 3D dose verification
• By optimizing the dose reconstruction algorithm and the I/O
performance, the delivered 3D dose distribution is verified in less than
200 ms per portal image, which includes the comparison between the
reconstructed and planned dose distribution.
Online EPID-based 3D dose verification
• By optimizing the dose reconstruction algorithm and the I/O
performance, the delivered 3D dose distribution is verified in less than
200 ms per portal image, which includes the comparison between the
reconstructed and planned dose distribution.
• The RMS of the difference
between the cumulative
planned and reconstructed 3D
dose distribution is used to
generate a trigger that can
stop the irradiation
Online EPID-based 3D dose verification
• By optimizing the dose reconstruction algorithm and the I/O
performance, the delivered 3D dose distribution is verified in less than
200 ms per portal image, which includes the comparison between the
reconstructed and planned dose distribution.
• The RMS of the difference
between the cumulative
planned and reconstructed 3D
dose distribution is used to
generate a trigger that can
stop the irradiation
• Irradiation of a polystyrene
slab phantom with a 10 MV
single arc VMAT prostate
treatment when a serious
error, the leaves were wide
open, was introduced.
The next step: on-line treatment verification
Conclusions
• Our automatic offline EPID-based dosimetry tool facilitated the large
scale clinical implementation of 3D in vivo dose verification of
IMRT/VMAT treatments, and was able to trace clinically relevant errors
Conclusions
• Our automatic offline EPID-based dosimetry tool facilitated the large
scale clinical implementation of 3D in vivo dose verification of
IMRT/VMAT treatments, and was able to trace clinically relevant errors
• It replaced pre-treatment verification, except for single fraction and
large field treatments, and may safe resources for other purposes
Conclusions
• Our automatic offline EPID-based dosimetry tool facilitated the large
scale clinical implementation of 3D in vivo dose verification of
IMRT/VMAT treatments, and was able to trace clinically relevant errors
• It replaced pre-treatment verification, except for single fraction and
large field treatments, and may safe resources for other purposes
• Our online 3D in vivo dose verification approach can be used to halt
the treatment machine in case of severe errors
Conclusions
• Our automatic offline EPID-based dosimetry tool facilitated the large
scale clinical implementation of 3D in vivo dose verification of
IMRT/VMAT treatments, and was able to trace clinically relevant errors
• It replaced pre-treatment verification, except for single fraction and
large field treatments, and may safe resources for other purposes
• Our online 3D in vivo dose verification approach can be used to halt
the treatment machine in case of severe errors
• 3D EPID-based in vivo dosimetry is a major step forward towards
optimal quality and safety in radiation oncology practice
Many thanks for your attention!
….. and special thanks to the EPID dosimetry
group at NKI-AVL:
•
•
•
•
•
•
•
•
•
Anton Mans
Hanno Spreeuw
Igor Olaciregui-Ruiz
Jan-Jakob Sonke
Marcel van Herk
Patrick Gonzalez
René Tielenburg
Roel Rozendaal
Ron Vijlbrief
Future developments
• To use deformable image registration algorithms to automate
registration of CBCT scans to planning CT contours, calculate a
new plan and compare the new 3D dose distribution with the
measured 3D in vivo dosimetry results
Future developments
• To use deformable image registration algorithms to automate
registration of CBCT scans to planning CT contours, calculate a
new plan and compare the new 3D dose distribution with the
measured 3D in vivo dosimetry results
• Preliminary results of the variation in plan characteristics during
a series of VMAT treatments of 20 H&N patients showed only
small changes in the D50 of the PTV
Future developments
Incorporate setup deviations in the analysis
Implement alert criteria based on DVH analysis
(currently manual evaluation)