Monte Carlo Dose Calculation
Monte Carlo Dose Calculation
for Radiotherapy Treatment Planning
for Radiotherapy Treatment Planning
C-M Charlie Ma, Ph.D.
Chetty I, Curran B, Cygler J, DeMarco J, Ezzell G, Faddegon B, Kawrakow I, Keall P, Liu
Department of Radiation Oncology
Fox Chase Cancer Center
Philadelphia, PA 19111, USA
What is Monte Carlo ?
(a mathematical method using random sampling)
H, Ma CC-M, SheikhSheikh-Baghery D, Rogers D, Seuntjens S, Siebers S.
The AAPM Task Group 105 Report
Med Phys (2007) 34: 48184818-53
Why call it Monte Carlo?
• The originators : Von Neumann and Ulam 1949
• The method : Random sampling from pdf’
pdf’s to
construct solutions to problems.
John Von Neumann
Stanislow M. Ulam
(1903-1957)
(1909-1984)
After the city in the Monaco principality ...
1
Photons
What is Monte Carlo
Radiation Transport?
• Random sampling of particle interactions
a good supply of random numbers
e-
probability distributions governing the physics processes
e+
• Information obtained by simulating large
number of histories
CPU time required
1 Gy => 1 billion electrons
1% uncertainty for 0.3 cm cubes requires a few
million electrons (hours on a PC)
1 Gy => 1000 billion photons
1% uncertainty for 0.3 cm cubes requires up to
a few billion photons (days on a PC)
Applications of M-C in radiotherapy
•
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•
•
•
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Fluence and spectrum calculations
Dosimetric parameters (stopping powers, etc.)
Correction factors (BSF, HS, PS, P/S ratio...)
Dosimeter response simulations
Treatment head simulations
Treatment planning dose calculations
2
Comparisons of Pencil Beam and Monte Carlo
Correction factor for
bone
for
factor for
bone6 MV photons
Correction
Mohan et al (1997)
Cl2300 C/D 6MV
1.20
Conventional Method (Pencil Beam)
PEREGRINE
1.15
calculated by FOCUS
measured with ion chamber
calculated by EGS4/DOSXYZ
water
1.10
bone
1.05
water
1.00
70 Gy
0.95
70 Gy
Tumor
0.90
0.85
0.80
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
16.0
cm
Depth (cm)
DVH Comparison
Dose Verification for IMRT
(Pawlicki et al 2000)
100
MC
Corvus
Monte Carlo
Corvus
Gy
16.2
14.4
12.6
9.0
5.4
1.8
Volume (%)
80
60
GTV
RT Lung
40
20
Cord
0
0
5
10
15
20
Dose (Gy)
3
Simulation of Clinical
Accelerators
Implementation of MCTP
• Accelerator simulation
• Source modeling
• Beam commissioning
• CT data conversion and phantom setup
• Dose calculation algorithms
• Data processing and plan evaluation
• Plan optimization
Tissue Type/Mass
Type/Mass Density Determination
(Pawlicki 1998)
1998)
CT Number to Medium Conversion
0.05
2.5
512 x 512
128 x 128
teflon
2000~2.088g/cm3
64 x 64
0.03
125~1.101g/cm3
0.02
-700~0.302g/cm3
-950~0.044g/cm3
0.01
-1000~0.001g/cm3
Mass density (g/cm^3)
Frequency
0.04
2.0
1.5
Skeleton - Ribs
polycarbonate
Vertebral body
water
polyethylene Alderson Muscle
1.0
0.5
Alderson Lung
air
0.00
0.0
0
200
400
600
800
CT Number
1000
1200
1400
0
500
1000
1500
2000
2500
CT Number
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M-C Simulation Geometry
Source plane
contours
Density map
Medium map
CT phantom
Beam modifier
Monte Carlo Algorithms
Current Status of MCTP
• Electron beams reported
VMC
DOSXYZ
MCDOSE/MCSIM
PENELOPE
MCRTP
DPM
• Photon beams reported
XVMC
PEREGRINE
MCNP
DOSXYZ
MCDOSE/MCSIM/MCRS
Accuray
BrainLab
NOMOS
Varian
CMS
Nucletron
AAPM
TG157
Survey
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Measured vs MC Reconstructed Dose Distributions
Beam Commissioning for MC
18 MV
40cmx40cm
6 MV
40cmx40cm
Yang et al, Phys Med Biol (2004) 49: 2657-73
Combined Dose Distribution: Film vs Monte Carlo
Calculations vs. Measurements
Delivery in film phantom
Patient plan (Corvus)
Monte Carlo dose
calculation
inferior
312 cm
cm from
fromisocenter
isocenter
superior
Energy
4 MV
CORVUS
Meas
M-C
2.177 Gy 2.177 Gy 2.201 Gy
15 MV
2.146 Gy 2.161 Gy 2.276 Gy
Lee et al (2001)
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Treatment Plan Comparison
Prostate
Corvus
Monte Carlo
Gy
77.2
70.0
56.1
48.9
35.0
27.8
21.1
13.9
Treatment Plan Comparison
Prostate
T11T11-L1 Vertebra
100
Volume (%)
Monte Carlo
MC
Corvus
80
Prostate
60
Bladder
40
20
Rectum
Gy
17.6
15.6
13.7
11.7
9.8
7.8
5.9
3.9
2.0
Corvus
0
0
15
30
45
60
75
90
Dose (Gy)
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T11T11-L1 Vertebra
CyberKnife Case Study
100
MC
Corvus
Volume (%)
80
GTV
60
40
Cord
20
0
0
5
10
15
20
Dose (Gy)
Comparison of Dose Distribution
Variation of Dose Kernels with Density
12.5 cm depth
5 cm depth
High-density medium
Low-density medium
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Variation of Dose Kernels with Density
Beamlet Dose Distributions
High-density medium
FSPB
Monte Carlo
90
70
50
5
Low-density medium
90
70
50
5
High-density medium
The accuracy depends on how it is implemented.
Pawlicki and Ma (2001)
Effect of Couch Bar on IMRT Dose Distribution
Attenuation for 18 MV photons
40
Other Applications for Advanced RT
d=3.3cm calculated
d=3.3cm measured
d=10cm calculated
d=10cm measured
Relative Dose (%)
30
Without bar
20
10
0
-20
-10
0
Off-axis Distance (cm)
10
20
MC vs film measurement
Yang et al 2005
With bar
9
Effect of Couch Bar on IMRT Dose Distribution
100
bladder-no bar
rectum-no bar
CTV-no bar
bladder-with bar
rectum-with bar
CTV-with bar
80
60
40
bladder - no bar
rectum - no bar
CTV - no bar
bladder - with bar
rectum - with bar
CTV - with bar
80
Volume (%)
Volume (%)
Monte Carlo
DVH Data
18MV DVH
100
20
0
TPS
IMRT using 6 MV photons
IMRT using 18 MV photons
60
40
20
0
100
50
150
Dose (cGy)
200
250
300
0
0
100
Dose
50
150
200
Yang et al 2005
Dose Volume Histogram (H&N)
100
Pencil beam
Monte Carlo
Volume (%)
80
MC for Modulated Electron RT
Target
LT Eye
60
40
Optic chiasm
20
0
0.0
10.0
20.0
30.0
40.0
50.0
60.0
Dose (cGy)
10
MU real patient vs.water tank
MU real patient vs.water tank
(MC / Water tank= 292 / 256=1.14)
Target 1,2 MC
based MU
Target 1,2 water tank
based MU
Lt eye water
tank based
Lt eye MC
MU
based MU
Rt eye water
tank based
MU
Rt eye MC
based MU
Courtesy of Joanna Cygler
Internal mammary nodes
(MC / Water tank= 210 / 206=1.019)
Isodose Distributions of MBRT for
Hypofractionated Breast Treatment
A. Photon IMRT
Courtesy of Joanna Cygler
58.0Gy
56.0Gy
47.3Gy
45.0Gy
42.8Gy
40.5Gy
36.0Gy
31.5Gy
22.5Gy
13.5Gy
4.5Gy
B. Electron beam
C. Combined dose
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Mixed Beam Breast Plan
Statistics and Denoising
Optimize IMRT based on
Optimize IMRT and the
Optimize IMRT
a fixed e- field
e- field weight
and MERT
Xiong et al (PMB 2004)
Statistics and Smoothing Techniques
Dose Prescription
Smoothing or denoising is safe
at 3-4% statistical level
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CTV or PTV
Dose Prescription
Dose to what medium?
4% stats
2mm σ
4mm σ
9%
5%
3%
1%
Dose prescription based on
DVH and isodose distributions
Dose to Water or Dose to Medium?
Summary
• MC dose calculation is becoming a practical
tool for advanced radiotherapy treatments
• The accuracy of MC dose calculation
depends on the implementation
• The potential of MC dose calculation
remains to be explored
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Acknowledgments
The FCCC/Stanford Monte Carlo Team
Charlie Ma
Bob Price
Lili Chen
Eugene Fourkal
Jinsheng Li
Lu Wang
Yan Chen
James Fan
Teh Lin
Max Jin
Steve Jiang
Todd Pawlicki
Jun Deng
Bilal Shahine
Ajay Kapur
Michael Lee
Qianyi Xu
Iavor Veltchev
Alain Tafo
Ahmed ElDib
Francis Tang
Sotirios Stathakis
Jay Chen
Wei Luo
Jie Yang
Lihong Qin
Meisong Ding
Omar Chibani
Grisel Mora
Thai Bing Nguyen
William Xiong
Antonio Leal
Freek Du Plessis
Thank You
FCCC Monte Carlo course, April 2010
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