Time-dependent dose guided radiotherapy (DGRT) with ... - Varian

Time-dependent dose guided radiotherapy (DGRT) with
electronic portal imaging as a patient QA and research tool
S Nijsten, M Podesta, L Persoon, W van Elmpt,
F Verhaegen
MAASTRO Clinic, Maastricht, the Netherlands
1

Dose Guided RadioTherapy (DGRT):
measuring true daily patient dose
2

What is the place of DGRT in the radiotherapy chain?
DGRT
IGRT 3

MAASTRO DGRT Philosophy
You need to know the true daily delivered 3D dose
You need to know the true delivered total 4D dose over the treatment
(possibly also 4D dose rate)
H
O
W
?
Combine all your verification imaging tools
Develop new verification imaging tools/methods
Make these tools/methods fast
With all the information collected, develop optimum methods for ART
Integrate in clinic
4

• EPI dosimetry
DGRT with EPI
– Point dose (1D) verification
– Pre-treatment 2D dose verif (no pt)
– Transit 2D dose verif (+ pt)
– Pre-treatment 3D dose verif (no pt)
– Transit 3D dose verif (+ pt)
– Pre-treatment time-dependent 2D dose verif (no pt)
– Transit time-dependent 2D dose verif (+ pt)
EPID
patient
EPID
– In-vivo time-dependent 3D dose verif (+ pt) = 4D EPID dosimetry
• Daily pt imaging (Cone beam CT, 3/4DUS, image
registration)
• Decision tools for Adaptive RT
• Trials
5

Four components of 2-D EPID dosimetry
Pre-treatment
dose prediction
Transit
dose prediction
EPID
dosimetry
Gamma
calculation
EPI dose
conversion
6

Gamma
calculation
Original distribution
(γ from 0 to 1)
Gamma calculation and visualisation
(� criterion of 3%, 3 mm)
Dose difference coding
(γ from -1 to 1)
Pass/fail coding
EPID measures more dose
EPID measures less dose
7

8
30-70x faster

Pre-treatment
dose verification
Verification I: Pre-treatment dose verification
(S Nijsten, W van Elmpt et al., Med. Phys. 34, 2007)
� detect errors in transfer between
TPS and linac
� detect malfunctioning of linac
(machine output variations, MLC errors,
beam flatness…)
9

Pre-treatment
dose verification
Pre-treatment dose verification for IMRT of H&N
(� criterion of 5%, 5 mm)
Predicted PDI Measured PDI Pre-treatment �
Before the start of treatment, for every patient the treatment fields are delivered and
measured with the EPID
10

Transit dose
verification
Verification II: Transit dose verification
(W van Elmpt, S Nijsten et al., Med. Phys. 32, 2005)
(S Nijsten, W van Elmpt et al., Med. Phys. 34, 2007)
� detect patient-related delivery errors
(set-up errors, organ motion, weight loss,
changes in fixation, …)
11

Transit dose
verification
No pt in beam
+ pt in beam
Predicted pretreatment
PDI
Transit dosimetry for tongue cancer treatment
(� criterion of 5%, 5 mm)
Measured pretreatment
PDI Pre-treatment �
Predicted transit
Measured transit
Transit �
PDI PDI
12

Five components of 3-D EPID dosimetry
3-D in-vivo
dose verification
Pre-treatment
dose verification
EPID
dosimetry
Dose
recalculation
3-D image
acquisition
CBCT
EPI dose
conversion
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It is possible to distinguish beam and patient related
delivery errors (Using only 3D transit dose reconstruction)
Beam delivery error
MLC error
Patient related delivery error
decrease in lung fluid + setup error
1
2
Planning CT Repeat CT or CBCT
= representation of
pt today
Backprojection
through pt
Detection of
composite
delivery errors
2
2
Detection of
beam
delivery errors only
2
1
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Axial
Coronal
Sagittal
Beam and patient related delivery errors
(Reconstructed 3D dose distributions)
Prescribed 3D dose in TPS
3D dose with
beam delivery errors only
3D dose with
patient related delivery errors only
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Varian TrueBeam
Volumetric Modulated Arc Therapy (VMAT):
Time-resolved (4D) dosimetry
DRR per control point
Transit dose per control point
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VMAT: Time-resolved EPID images
(=‘fluoroscopy’)
Time-resolved EPID during treatment:
�allows investigating causes of differences between predicted
and measured dose
Time series (‘film’)
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Pre-treatment dose prediction; per control point
Fluence map
Predicted
primary PDI
Predicted EPI
scatter PDI
EPID
+ =
Pre-treatment
Predicted total pretreatment
PDI
18

Pre-treatment dose prediction; integrated over 1 beam direction
Fluence map
Predicted
primary PDI
Predicted EPI
scatter PDI
EPID
+ =
Pre-treatment
Predicted total pretreatment
PDI
19

Transit dose prediction; integrated over 1 beam direction
Predicted
primary PDI
Predicted
scatter PDI
+ =
Predicted total
transit PDI
20

One control point
Gamma calculation
Integrated dose
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Varian Research project: TimePort
Time-resolved pre-treatment 2D portal dosimetry
• Dosimetry verification of RapidArc treatment (+FFF)
• Hypothesis: Beam delivery with a Varian RapidArc linac can, pretreatment,
be verified accurately and fast without the need for
phantom measurements using time-resolved EPID dosimetry
Total accumulated calculated portal
dose for entire arc treatment
Measured total portal image
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Clinical workflow for routine treatment verification
@ MAASTRO CLINIC – EPICORE SYSTEM (3D)
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Planning CT
Second CT
Before fx 4
Third CT
Before fx 18
Application:Trends in dose discrepancies;
A lung cancer case
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Monitoring dose delivery over the whole treatment
course
CT2 fraction (#) PLAN 2
CT3
field (#)
field (#)
4 5 6 7 8 9
fraction (#) PLAN 3
18 19 20 21 22 23
4 8 12 16 20 24
18
40
20 25 30 35
25

A side story: DGRT on small animal irradiation/imaging system
(pre-clinical)
15 x 1mm
beams
Predicted EPI Measured EPI �(5%,0.8mm)
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Conclusions & Outlook
• DGTR provides powerful tools for decision making in
adaptive RT
– 2D pre-treatment/transit dosimetry
– 3D pre-treatment/transit dosimetry
– Separate machine from patient errors
– Separate systematic from random patient errors
• Ongoing:
– Time-resolved EPI dosimetry (‘4D’)
– Clinical integration
– Patient data analysis for different cancer sites
– Decision models 27