Monte Carlo - II: Clinical impact
Monte Carlo for
Electron Beam Treatment Planning
C-M Charlie Ma, Ph.D.
Dept. of Radiation Oncology
Fox Chase Cancer Center
Philadelphia, PA 19111
Why Use Monte Carlo for
Radiotherapy Treatment Planning
An accuracy of about 5% in dose
delivery is required to effectively treat
certain types of cancers and to reduce
complications.
ICRU Reports 24 (1976) and 42 (1988)
Outline
• Current status of electron Monte Carlo
• Implementation of Monte Carlo for electron
beam treatment planning dose calculations
• Application of Monte Carlo in conventional and
modulated electron beam therapy
• Monte Carlo for other beam modalities
The Accuracy Requirement for
Treatment Planning Dose Calculation
σ2=σ2calib+σ2dose+σ2setup+σ2motion +…
and
σ ≥ 2σdose=5%
then
σdose=2.5%
Uncertainties in Electron Beam Dosimetry
Limitations of dose calculation algorithms
source models
Fluence Profiles from an eMLC
A
B
A
B
Beam modifier effect
heterogeneous patient anatomy
Limitations of dose measurement systems
non-calibration conditions
complex beam modifier geometry
Jin et al (AAPM 2007)
Pencil Beam Pinnacle3
Monte Carlo (BEAM)
Achterberg et al (ESTRO 1999)
Pencil Beam Pinnacle3
Monte Carlo (BEAM)
Achterberg et al (ESTRO 1999)
20 MeV Beamlet Distributions
Monte Carlo (MCDOSE)
Pencil Beam (FOCUS)
Monte Carlo Codes
for Electron Beam Dose Calculations
• The BEAMnrc/DOSXYZnrc system
• Voxel Monte Carlo (VMC)
• Macro Monte Carlo (MMC)
• Superposition Monte Carlo
• Other programs (ITS, MCNP, PENELOPE)
• EGS4/MCRTP/MCDOSE/MCSIM
Ma et al (PMB 2000)
Commercial Implementation
• Nucletron Oncentra MasterPlan (2001)
– Implementation of Kawrakow’s VMC++ Monte
Carlo dose calculation algorithm (2000)
• Varian Eclipse eMC (2004)
– Based on Neuenschwander’s MMC dose
Timing – Nucletron Oncentra MasterPlan
•
•
•
•
•
10x10 cm2 applicator
50k histories/cm2
Anatomy - 41 CT slices
Pentium 4 Xenon 2.2 GHz
Calculation time
– 1.5 minutes for 6 MeV beam
– 8.5 minutes for 20 MeV beam
calculation algorithm (1992)
Faster than pencil beam!
Courtesy of Joanna Cygler
Eclipse eMC no smoothing
Implementation procedures
Voxel size = 2 mm
Air
• Modeling of clinical electron beams
Air
120
110
100
90
80
depth = 6.7 cm
70
60
50
depth = 7.7 cm
40
18 MeV
depth = 4.7 cm
80
70
60
50
40
30
• Dose calculation, data processing and display
110
90
RelativeDose
• CT data and beam setup conversion
120
depth= 4.7cm
18 MeV
100
Relative Dose
• Commissioning of clinical electron beams
4.7 cm
Bone
Bone
20
Measured
eMC
30
Measured
eMC
20
10
10
0
0
-6
-4
-2
0
2
4
6
-6
Off-axisX position /cm
-4
-2
0
2
4
Off-axisY position /cm
Ding et al (PMB 2006)
Effect of voxel size and smoothing
MU real patient vs.water tank
(MC / Water tank= 292 / 256=1.14)
Air
Air
2mmandnosmoothing
18 MeV
110
Relative Dose
100
90
80
70
2mmandwith3Dsmoothing
60
5 mm and with 3D smoothing
50
120
Relative Dose
120
110
4.7 cm
Bone
Bone
40
5 mm and with
3D smoothing
90
80
70
60
50
2 mm and with 3D smoothing
40
30
2mmandnosmoothing
18 MeV
100
30
depth = 4.9 cm
20
20
10
depth = 4.9 cm
10
0
0
-6
-4
-2
0
2
4
6
Off-axisX position /cm
-6
-4
-2
0
2
4
6
Off-axisY position /cm
Ding et al (PMB 2006)
Courtesy of Joanna Cygler
6
MU real patient vs.water tank
Internal mammary nodes
(MC / Water tank= 210 / 206=1.019)
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
Monte Carlo for
Mixed Beam Treatment for Breast
Combined Photon/Electron Plan Based on MC
• Conventional (46 Gy, 14 Gy boost)
Photon beams to whole breast: 23 fractions, 2
Gy/fraction
Electron boost to tumor bed: 7 fractions, 2 Gy/fraction
• Hypofractionated (45 Gy, 56 Gy)
IMRT to whole breast: 2.25 Gy x 20 fractions
IMRT/MERT to tumor bed: 2.8 Gy x 20 fractions
Courtesy of Jinsheng Li
58.0Gy
56.0Gy
47.3Gy
45.0Gy
42.8Gy
40.5Gy
36.0Gy
31.5Gy
22.5Gy
13.5Gy
4.5Gy
Courtesy of Jinsheng Li
Conclusions
• Monte Carlo is a useful tool for radiotherapy
treatment planning & dose verification
• Monte Carlo has a more important role in
electron dose calculation
• High accuracy, high efficiency, low cost
• More work is needed to make it clinically
available