Fricke Gel dosimetry by means of visible light
transmission imaging: State of the Project at
University of Cordoba
Mauro Valente & Victor Galván
CONICET & FaMAF-Universidad Nacional de Córdoba, Argentina.
Glossary and Outlines
 Modern Radiotherapy: Demand of accurate 3D dosimetric systems
• Current dosimetry techniques and Fricke gel dosimeters
 Fricke gel dosimetry I: Preparation and characterization & ferric ion diffusion
• Background
•
•
•
Optimizations and Developed preparation Protocol
Dose-response characterization and Tissue-Equivalence study
Diffusion coefficient determination & Correction with time-deconvolution algorithms
 Fricke gel dosimetry II: Suitability of FGD layer imaging & preliminary tests
•
•
Characterization of the optical system & Limitations of the technique
Photon and electron beam characterization
•
Comparisons with simulation of unique beam irradiations & Complex techniques
simulations (Dynamic and multiple field radiotherapy)
 Fricke gel dosimetry III: Dedicated software & 3D dose imaging
• Image recognition Dedicated algorithms for dose distribution calculation
• Target volume by means of Fricke gel layer dosimeters
• Dose Imaging: 3D reconstruction & “AQUILES – Real 3D”: a novel tool for 3D dose
Imaging
 Fricke gel dosimetry IV: Non conventional (mixed fields) dosimetry & BNCT
•
Versatility for advance (non conventional) dosimetry
•
Boron Neutron Capture Therapy (BNCT) applications
 Fricke gel dosimetry V: Project at the University of Cordoba (ARG)
• Current state of the Project for Fricke Gel layer –optically analyzed- dosimetry.
Modern Radiotherapy: “Complex” irradiation techniques
During the last years, significant developments in
Radiotherapy techniques, mainly due to the increasing
technology and computer capability

Conformal Radiotherapy

Dynamic Radiotherapy

Radiosurgery

Intraoperative Radiotherapy

High dose rate Brachitherapy

Micro Beam Radiotherapy (mBR)

Intensity Modulated RadioTherapy (IMRT)
Current traditional dosimeters
Charact.
Dose Integ.
High Resol.
T-E
En. Ind.
DR Ind.
3D
Lect. Stability
Ori. Ind.
Rel. L-C C-Av.
Short T-C
Ion. Ch.
TLD
Diode
Film
Fricke Gel
Fricke gel dosimetry
• Continuous chemical dosimeter
• Based on ferrous sulphate solution
• Chemical yield: Fe2+→ Fe3+
• Fixed to gel matrix (Spatial resolution)
• Originally imaged by MRI
Suitably shaped in form of thin layers





Negligible alteration of in-phantom transport
properties
Suitable for visible light tranmittance analysis
Not complicated correction algorithms (ref. Index
variation)
Versatility regarding chemical composition
Important advantages for neutron field irradiations
(dose contribution separation)
Fricke gel main Preparation Procedure
1.
2.
3.
4.
5.
6.
7.
8.
Gel powder is combined with half of the total quantity of water
Solution is heated (constant stirring and monitoring of temperature)
Solution is maintained at 45 °C for 20 minutes (gel powder dissolution)
Separate flask: Fricke (fer. sulph., sulp. acid), and XO with rest of the water
Gel solution led to cool until Fricke solution is added (T=42-40ºC)
Mixed solution should become clear, transparent orange
Final solution is transferred into pre-elaborated suitable containers
Normal T, P conditions for 10 minutes. Put batches (at least 12 hours) into
the fridge (T=6-10ºC)
Developed dedicated PROTOCOL
Fricke Gel
solution
Optical imaging method for Fricke gel layer dosimeters
Spectroscopy Analysis
Standard Fricke solution: Absorption peak around 302nm


Fixing standard Fricke solution to gel matrix (information spatially firmed)
Adding X.O. (marker) → Abs. peak displacement (580nm) and Diffusion
slow down
Visible light (yellow-orange)
… therefore, optical analysis by means of visible light
transmittance becomes suitable for Fricke gel dosimetry
Fricke gel dosimeter Imaging: Optical system
Detector
(CCD)
Monochr. filter
Dosimeter
Dark mask
Illuminator (homog. plane
paral. visible light beam)
Transmittance measurement
Interaction Process: material (μa, μs) – Inc. beam (parallel filtered polychr.)
Radiation Transport Equation


sˆ     a   s  I r , sˆ    s  I r , sˆ   S

 I r , sˆ  

2





s
ˆ
,
s
ˆ
'
I
r
,
s
ˆ
'
d
sˆ '

 I z 
z
   sˆ, sˆ '  d
 max
   a   s  I  z    s I  z 
2
sˆ '  1
    sin   d 
 min
  sˆ, sˆ '   f  sˆ  sˆ '     sˆ, sˆ '     
Bouger-Lambert-Beer Law
I  z   I 0  exp    a   s  z 
A   log 10 T 
ACd
Beer’s Law (Abs.):
Fe3+ chemical yield:

 C Fe
3

A
 Fe
3


 I inc
 I 0   
1
 
  log 10 

log 10  fin
3
 I  z  d     C  Fe 3    Fe
I







ABSORBED DOSE CORRELATED TO Fe3+ CONCENTRATION,
MEASURABLE BY MEANS OF TRANSMITTANCE IMAGES
 
D  f  C Fe
3
 
 GL Before
D  log 10 
After
GL






D   C Fe
GL  f ( I )   I
3


 cte 
Fricke gel layer dosimeter dose-response
The dosimeter dose response depends on several factors, but it has been shown
that under proper conditions, dose response is linear to some extent.
Characterization of some parameters affecting dosimeter dose-response
0.7
0.6
0.5
OD
0.4
0.3
0.2
0.1
0.0
0
10
20
30
40
50
Dose [Gy]
Fricke dosimeter (3% GPS) layer dose response curve and linear fit up to 30
Gy for a 18 MV photon beam.
Ferric ion diffusion in Fricke gel layer dosimeters
Diffusion effect in Fricke gel dosimeters. Gel matrix is used to locally fix the XOinfused ferrous sulphate solution, enabling spatial resolution due to the slowing
down in the movement of the ferric ions produced.
Dose distribution is deteriorated: Limitation of Time interval for sample imaging
Accurate dose distribution measurements: Prompt Imaging or
Correction Algorithms
TASK
Diffusion is a convolution process
→
distributions at any time with the initial one.
correlation between concentration
Full description of the ferric ion diffusion effect:
 3D solution of the diffusion equation
 Considering steepness of the concentration distribution.
Diffusion model and diffusion coefficient calculation
D-E derived from: 1. Langevin equation (considerating Brownian motion)
2. Fokker-Planck equation (evolution of stochastic systems)

 P r , t 
t

2


D r , t  P r , t 
1D approach for the diffusion coefficient calculation



Suitable initial dose distribution: Step-Function (Heaviside)
Experimental Arrengement: dedicated cerrobend blocks
conforming circular (Ǿ=3cm) and rectangular (4x2cm2)
12MeV electron beam F.S.=5x5cm2
2D approach for the diffusion coefficient calculation



Suitable initial dose distribution: Almost-punctual (Dirac Delta)
Experimental Arrengement: dedicated cerrobend block with hole
circular (Ǿ=1mm)
12MeV electron beam F.S.=10x10cm2
Diffusion: 1D Approach
0.40
0.40
0.35
0.35
0.30
0.30
0.25
0.25
0.20
0.15
2
0.10
0.10
0.05
0.05
0
2
4
6
8
10
12
14
16
0
2
time (h)
 x  x  
0
P ( x, t )  A erf 

 2 D t  t 0  
T=3000min
2
0.20
0.15
1D solution
T=1200min
 (cm )
D t
0
T=900min
2
P 
1 P
T=600min
2

2
T=300min
 (cm )
T0
D
1D
 (1 . 24  0 . 07 ) mm h
2
1
4
6
8
10
12
14
16
time (h)
Square of 1D Gaussian spreads in function of time and linear fit for rectangular shape
(left) and circular shape (right).
350
300
 ( OD )
2D
  2    0 2
A
 y0 
exp 
2
w
w 2




2
2
w (pix )
250
200
150
D
100
50
0.5
1.0
1.5
2.0
2.5
Time (h)
3.0
3.5
4.0
380 pix:= 130mm
Square of Gaussian spreads as a
function of time and linear fit.
2D
 (1 . 15  0 . 05 ) mm h
2
1
Fricke gel layer dosimeters: Unique Beam
Application to Photon (Gamma and high energy R-X) beams
Ion. Chamber
MC Simulation
Fricke Gel
100
90
70
60
PDD
90
Normalized Dose
80
50
40
30
20
Ion. Chamber
MC simulation
Fricke Gel
100
80
70
60
50
40
30
20
10
10
0
0
0
1
2
3
4
5
6
7
Depth (cm)
60Co
8
9
10 11
-10
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
Beam Width (cm)
Gamma Beam (F.S.:10x10cm2, SSD:80cm)
Application to Photon (Gamma and high energy R-X) beams
100
Normalized Dose
90
80
70
60
PDD
Film dosimeter
MC Simulation
Fricke Gel
Film dosimeter
100
MC Simulation
90
Fricke Gel
50
40
30
20
10
80
70
60
50
40
30
20
10
0
0
0
1
2
3
Depth (cm)
4
5
6
0
1
2
3
4
5
6
7
8
9
10
Beam Width (cm)
6MV Beam Varian 600C (F.S.: 10x10cm2, SSD:100cm)
Application to Photon (Gamma and high energy R-X) beams
Ion. Chamber
MC Simulation
Fricke Gel
100
90
100
80
90
PDD
60
50
40
30
20
10
80
Normalized Dose
Ion. Chamber
Fricke Gel
MC Simulation
70
70
60
50
40
30
20
10
0
0
0
1
2
3
Depth (cm)
4
5
6
-10
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
Beam Width (cm)
10MV Beam Varian 18 (F.S.: 10x10cm2, SSD:100cm)
Application to Photon (Gamma and high energy R-X) beams
Ion. Chamber
MC Simulation
Fricke Gel
100
90
Normalized Dose
80
70
PDD
60
50
40
30
20
10
Ion. Chamber
Fricke Gel
MC Simulation
100
90
80
70
60
50
40
30
20
10
0
0
0
1
2
3
4
5
6
7
Depth (cm)
8
9
10 11
-5
-4
-3
-2
-1
0
1
2
3
4
5
Beam Width (cm)
18MV Beam Varian 2100 (F.S.: 5x5cm2, SSD:100cm)
Application to high energy electron beams
Ion. Chamber
MC Simulation
Fricke Gel
100
80
PDD
60
40
20
0
0
1
2
3
4
5
6
7
8
9
10 11
Depth (cm)
16MeV Beam Varian 2100 (F.S.: 10x10cm2, SSD:100cm)
Application to high energy electron beams
Ion. Chamber
MC Simulation
Fricke Gel
100
80
PDD
60
40
20
0
0
1
2
3
4
5
Depth (cm)
6MeV Beam Varian 18 (F.S.: 20x20cm2, SSD:100cm)
AQUILES: Dose Imaging software
• MatLab environment
• Dedicated algorithms for Image
recognition, process and analysis.
• User Graphic Interface
• Algorithm and Numeric Methods
Optimization (speeding up)
Calculation Algorithms - AQUILES:
 GL 1P i, j    PP12 GL 1P i, j   ...   PPN1 GL PN i, j  
D i, j    log 10 

D1
D
DN
D





GL
i
,
j

...


GL
i
,
j
P1
1
P1
N



2
 D i, j    


D


  
2

 N 
D
2
  GL  
   GL P
i 1
i
 
2
  D
 
   GL D
i
 




2
  N 
   D

    Pi P
i2  
   P1
γ
0.45
0.40
0.35
κ
OD
0.30
0.25
0.20
-
OD(16MeV e )= 0.0144D
0.15
OD(
137
Cs)= 0.0139D
0.10
0.05
5
10
15
20
Dose (Gy)
25
30
35
2


2
  P  D
 i
   Di P

 P1
 
2


2
  D  D
 i
   D1P

 P1
 
2

  D1
 1

 
2




 
AQUILES: Application Examples
IMRT: FGD layer dosimetrey & TPS data process and analysis
AQUILES – Real 3D: Versatile AQUILES subroutine for
accurate 3D dose Imaging
AQUILES – Real 3D
AQUILES – Real 3D:
Application Great capability for
3D dose Imaging
Multiple
Volumes
Isodose
3D
Dynamic
dose Imaging
radiotherapy
byof
means
(90ºof
Arc
7Visualization
piled
tenchnique)
up Fricke gel
layer
bydosimeters
means of dedicated
for Multiple-Field
MC simulations
(Box) technique
Cortesy: Image from M. Valente PhD Thesis
600
Y Axis [pixel]
500
400
10
70
80
300
60
200
40
30
20
50
100
50
100
200 distribution
250
HDRB: Scanner Image
(right) 150
and Dose
X Axis [pixel]
(left)
9.0
8.5
8.0
20
7.5
7.0
Y Axis Title
6.5
6.0
40
60
5.5
80
5.0
4.5
9080
4.0
40
3.5
20
90
60
3.0
2.5
2.0
2
X Axis Title
4
In terms of standard IMRT criteria for accuracy (GammaFricke
gelmeasurement
layer dosimeter
(up) and TPS
Function)
this
represents
the (bottom)
best one ever
a typicalFilm,
IMRT (non-perpend.
beam)
donefor(EPID,
scanning Sys)
at Irradiation
an important
Radiotherapy Institute
State of the Project at University of
Cordoba (ARG)
•Proper Laboratory facility: OK (already accomplished!)
•Fricke gel dosimeter preparation: OK (already accomplished!)
•FGD optical properties characterization: OK (already accomplished!)
•Adaptation of test radiation facility: OK (already accomplished!)
•Dedicated facility design & construction for FGD optical analysis by means of visible light transmission:
OK (already accomplished!)
•Characterization of optical analysis facility: Work in progress (curtrently perfomed)
•Available for multitask purposes: Coming soon ….
THANKS FOR YOUR ATTENTION!
This Study was partially supported by the Italian
government (results up to 2007) whereas argentine
entities like CONICET, ANPCyT and SeCyT-UNC have
supported and granted it since 2008.
GRACIAS POR SU ATENCIÓN!