Download - Sina Mossahebi
Evaluation of Electron Monte Carlo
Dose Calculation of RayStation
TPS in Heterogeneous Media
Sina Mossahebi, Ph.D., Mu-Han Lin, Ph.D.,
Mariana Guerrero, Ph.D.
Department of Radiation Oncology,
University of Maryland School of Medicine,
Baltimore, Maryland
Outline
• Background • RayStation Electron Monte Carlo Algorithm
• Heterogeneity Dose Evaluation • Straight incidence: dose at heterogeneous interfaces
• Oblique incidence: heterogeneity, oblique beam,
extended SSD
• Results
• Conclusions & Future Work
MC Electron Source Modeling
Use:
– Multiple Source Model
• Shape, size, position, energy of sources
Generate phase-space faster
Traditional Analytical E0
1
2 3
4 5
6
P, E’, (x,y,z), (u,v,w), w, 6
E0
1
2 3
4 5
6
P, E’, (x,y,z), (u,v,w), w, 6
Use:
– Source information
– Cross section interactions
– Position, shape, material of
each component
Generate phase-space Courtesy of Dr. Lin
RayStation EMC
Patient independent part
Analytical source modeling
• Effective energy and spatial-angular
distributions
Patient dependent part
– Component module
– Inexplicit transport
• Assumptions were made to
speed up the transport
• 1-10 % dose contribution
Phase
Space
Engine
Dose
Calculation
Engine Patient dose calculation
Courtesy of Dr. Lin
Commissioning in Homogenous Media
• RayStation MC algorithm for electron has been commissioned in homogenous media and is being used in our clinic
• PDD
• Profile
• Cone factor
• Cutout factor
• Point dose
Purpose of the Project
• Evaluate the dosimetric
performance of the electron
MC (EMC) algorithm of
RayStation (v.4.5) TPS for
clinical challenging scenarios
Heterogeneity,
Oblique angle,
Extended SSD, ...
Straight Incidence
RayStation
Polystyrene (2.5 cm)
Cork (5 cm)
Polystyrene (1.4 cm)
OSLDs
EBT
Film
Ion
Chamber
Cork (5 cm)
Experimental Setup (1)
– 6, 9, 16 MeV
– Open on a 15x15 cm2 cone , 3x6 cutout on a 10x10 cm2 cone
– 100 cm SSD
Ion Chamber vs RayStation
E
(MeV)
Field Size
(cm2)
Ion Chamber Dose
Measurement
(cGy)
RayStation Dose
Calculation (cGy) Difference (%)
6 3×6 2.9 3 2.5
9 3×6 56.9 59 3.6
16 3×6 131.0 127 3.2
6 15×15 4.1 4 2.9
9 15×15 121.0 119 1.6
16 15×15 176.9 182 2.8
Point dose comparison:
Low dose region
< 4%
difference
RayStation
Cork (5 cm)
Polystyrene (2.5 cm)
Polystyrene (1.4 cm)
Ion
Chamber
Cork (5 cm)
OSLD vs RayStation
E
(MeV)
Field Size
(cm2)
OSLD Dose
Measurement
(cGy)
RayStation Dose
Calculation (cGy) Difference (%)
6 3×6 170.0 173 1.8
9 3×6 172.8 172 0.4
16 3×6 192.1 187 2.7
6 15×15 190.3 189 0.7
9 15×15 181.5 179 1.4
16 15×15 191.0 193 1.0
RayStation
Cork (5 cm)
Polystyrene (2.5 cm)
Polystyrene (1.4 cm)
OSLDs Cork (5 cm)
Point dose comparison:
High dose region
< 3%
difference
2D Dose Evaluation at interface
Energy (MeV)
Gamma RayStation vs. EBT Film
6 >97%
9 >96%
16 >99%
100cmSSD, 10x10cone, 3x6 cutout
2D planar dose distribution
Gamma evaluation 3% / 3mm
RayStation
Cork (5 cm)
Polystyrene (2.5 cm)
Polystyrene (1.4 cm) Film
Cork (5 cm)
Passing rate
>95%
Horizontal Vertical
EBT film (reference) RayStation (target)
Oblique Incidence in Heterogeneous
Phantom Experimental Setup (2)
Axial View
Cork (5 cm)
Solid Water (6 cm)
Solid Water (2 cm)
Film
Cork (5 cm)
Solid Water (6 cm)
Solid Water (2 cm)
Sagittal View
Cork (5 cm)
Solid Water (6 cm)
Solid Water (2 cm)
10˚
20˚
45˚
Measurement Conditions
– 6, 9, 16 MeV
– 3x6 cutout on a 10x10 cm2 cone
– 0˚, 10˚ SSD = 100 cm
– 20˚, 45˚ SSD = 110 cm
(to avoid collision)
Axial View
Cork (5 cm)
Solid Water (6 cm)
Solid Water (2 cm)
Film
Cork (5 cm)
Solid Water (6 cm)
Solid Water (2 cm)
Sagittal View
Cork (5 cm)
Solid Water (6 cm)
Solid Water (2 cm)
10˚ 20˚
45˚
2D dose comparison between RayStation and EBT film measurement
Oblique Incidence 2D Depth Dose Distribution
6 MeV
EBT film (reference) RayStation (target)
0˚
10˚
20˚
45˚
16 MeV
EBT film (reference) RayStation (target)
0˚
10˚
20˚
45˚
Oblique Incidence
Axial View
Cork (5 cm)
Solid Water (6 cm)
Solid Water (2 cm)
Film
Cork (5 cm)
Solid Water (6 cm)
Solid Water (2 cm)
Sagittal View
Cork (5 cm)
Solid Water (6 cm)
Solid Water (2 cm)
10˚ 20˚
45˚
Gamma Passing Rate
SSD 100 cm 110 cm
Energy (MeV)
0˚ 10˚ 20˚ 45˚
6 98% 96% 66% 64%
9 91% 91% 81% 79%
16 83% 82% 69% 79%
10x10cone, 3x6 cutout
Gamma evaluation 3% / 3mm
Passing rate
>90%
Low passing rate with increase of
beam angle and SSD
Low passing rate at high energy
cork
Failing Regions of Low Energy Electron
(6MeV)
For low energy electron as beam angle and SSD increase:
• Acceptable at target region
• Failing at low dose region
• RayStation overestimates the dose about 10%
10˚ 20˚ 45˚
Vertical Dose Profile (PDD)
0˚
Gamma Pass\Fail
cork cork cork
Failing Regions of High Energy Electron
(16MeV)
For high energy electron:
• Acceptable at target region
• Failing at heterogeneity (low density)
• RayStation overestimates the dose about 10%
Vertical Dose Profile (PDD)
0˚ 10˚ 20˚ 45˚
Gamma Pass\Fail
cork cork cork
More energy deposition
Less energy
deposition
cork
Conclusions
Straight incidence
– The RayStation dose calculation had a good agreement with ion chamber
and OSLD measurements for different electron energies.
– Gamma analysis showed a strong agreement at the interface of high dose
region.
– Poor agreement at heterogeneity region for high energy electron beam:
RayStation overestimates the dose (dose to lung)
Oblique incidence
Gamma analysis showed
– Good agreement at target area.
– Agreement ↓ as oblique angle ↑ and SSD ↑
– Poor agreement at heterogeneity region for high energy electron beam.
Future Work
Further investigation is in progress for
– Extended SSD
– Oblique angle
– Higher energy (20 MeV)
– Various fields and cut-outs
– Different setups
Acknowledgements
• Mu-Han Lin, Ph.D.
• Mariana Guerrero, Ph.D.
Thank you!
Oblique Incidence 2D Depth Dose Distribution
9 MeV
EBT film (reference) RayStation (target)
0˚
10˚
20˚
45˚
16 MeV
EBT film (reference) RayStation (target)
0˚
10˚
20˚
45˚
Low Energy Electron (6MeV) Dose profile
Horizontal Dose Profile
Vertical Dose Profile
0˚ 10˚ 20˚ 45˚
Calibration Curves
6 MeV 9 MeV 16 MeV
Straight Incidence
Dose profile at polystyrene-cork interface
EBT film (reference) RayStation (target)
Straight Incidence
Horizontal dose profiles
EBT film vs RayStation dose profile
Vertical dose profiles
MC - Linac Simulation
History: a single particle sampled by the random number
Phase space file: a binary file storing the particle
information of the scoring plane.
- Particle type, energy, position, direction, weight, last
interaction position
E0
1
2
3 4
5
6
P, E’ , (x,y,z), (u,v,w), w, 6
More history, lower statistical uncertainty
100
101
102
103
104
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Mean Value
Statistical Errors
Courtesy of Dr. Lin
RayStation Electron Algorithm
• With the intention of significantly improving accuracy
of dose and MU calculation
phase space
engine
• Simulate what
comes out of
treatment head
2 separate “engines”
dose calculation
engine
• Simulate energy
transport and
scoring in patient
RayStation Monte Carlo