Dr. Mir Md. Akramuzzaman1, G.A. Zakaria2, G.H. Hartmann3
1Department of Physics, Jahangirnagar University, Savar, Dhaka, Bangladesh.2Gummersbach Academic Teaching Hospital, University of Cologne, Germany.3Department of Medical Physics in Radiotherapy, German Cancer Research Center, Heidelberg, Germany.
M. Anwarul IslamDepartment of PhysicsJahangirnagar University
Calculation of air-kerma strength and dose rate Calculation of air-kerma strength and dose rate constant for new BEBIG constant for new BEBIG 6060Co HDR brachytherapy Co HDR brachytherapy
source: an EGSnrc Monte Carlo studysource: an EGSnrc Monte Carlo study
To calculate the Air kerma strength for BEBIG 60Co source with Monte Carlo codes
To calculate the dose rate constant for BEBIG 60Co source with the protocol of TG-43 (AAPM)
To compare the calculated Air kerma strength with published or measured value
ObjectivesObjectives
BEBIG 60Co HDR brachytherapy source model
Using EGSnrc Monte Carlo codes developed by National Research Council (NRC) of Canada
Calculating the photon fluence rate in air with the source
Using the AAPM TG-43 protocol
Materials and Method Materials and Method
Monte Carlo Procedure
Filtering
Apply physical/ statistical
law/ theory
Group of Random Events
Analysis Apply Physical Law/theoryApply Boundary
Condition
Apply Statistical Law
Apply Probability theory
Applications of Monte Carlo
Computational Physics Physical Chemistry Quantum CromodynamicsHeat ShieldingAerodynamics Statistical Physics Molecular modeling Particle Physics Radiation Physics Energy Transport Stochastic Financial Modeling Telecommunication Mathematical Solution Weather Forecast Light transport in biological tissueReliability Engineering etc
Monte Carlo code for Radiation Transport
The following codes are available for the simulation of radiation transport : GEANT: simulation of high energy particles interacting with a detector.
CompHEP, PYTHIA: Monte-Carlo generators of particle collisions
MCNP(X): radiation transport codes
MCU: particles (electrons, photons, neutrons) transport code
Cont.
PEREGRINE: code for radiation therapy dose calculations
PENELOPE: code for coupled transport of photons and electrons
BEAMnrc: code system for modeling radiotherapy sources (Linac)
EGSnrc: code for coupled transport of electrons and photons
EGSnrc Monte Carlo codes
The EGSnrc Monte Carlo codes are used in this work. This code is very powerful research tool for radiotherapy field in brachytherapy.
The EGS (Electron-Gamma Shower) system of computer codes is a general purpose package for Monte Carlo simulation of the coupled transport of electrons and photons.
The EGSnrc codes developed by National Research Council of Canada
The EGSnrc is capable to calculate fluence, dose, stopping power ratio, kerma etc.
BEBIG 60Co HDR source models
Real geometry of the source
Model geometry of the source
Monte Carlo input of source model
Sagittal Section
Fig: Equal sagittal section for Monte Carlo source input
TG-43 Formalism
General 2D formalismThe general, two-dimensional ~2D dose-rate equation from the TG-43 protocol is retained,
Where, = dose rate at the point (r, θ)
Fig: Coordinate system used for brachytherapy dosimetry calculations
TG-43 Formalism
Using Formula for fluence calculation
( ) ( ) ΔE .ρEμ..E Eφ.101.602=(d)K ien
i
E
Ei
10air
max
min
′×′ ∑−
And finally, Sk/A = 2 × K΄air(d) × d2
Where,
(d)Kair′ is the total air-kerma at the distance, d and the unit is Gy/Photon
( )iEφ′ is the photon fluence per unit energy and it’s unit MeV-1 cm-2
( )ρEμ ien is the mass energy absorption coefficient and it’s unit cm2 gm-1
Ei is the energy spectrum and ΔE is the energy bin size
The factor 1.602×10-10 is required to convert Kair(d) from MeV gm -1 into Gy
Sk/A is the air-kerma strength per unit source activity. The unit is μGym2h-1.Bq-1 or UBq-1
D = 100 cm according to the TG-43 formalism
Calculation grid: Slab and radial thickness = 1-2 mm Photon cutoff energy = 0.001 MeV Electron cutoff energy = 0.521 MeV No. of history simulated for every point = 109 Dose for photon contribution simulated Considered one decay will result in the emission of 2
photons Average time per simulation is 5 hours for photon
Dose calculation formulaDose calculation formula
Dose calculation formulaDose calculation formula
The user-code DOSRZnrc is used to calculate, Dphotons
where Dphotons is the total dose by photons
Sk/A is air-kerma strength per source activity into [U Bq-1]
is the true dose rate per unit air-kerma strength for 60Co source in [cGy h-1 U-1]
)//(2106.3 5 ASD kphotontrueD ×××=•
Phantom ModelPhantom Model
Geometric Preview Window
Calculated point
Tissue basis absorbed dose calculationTissue basis absorbed dose calculation
Tissue Water Combone
Breast Blood Lung Adiposetissue
Muscle Softtissue
Testese
Densityg/cm3 1.00 1.85 1.02 1.06 0.26 0.92 1.12 1.0 1.04
Some body equivalent tissues (shows in table below) are simulated to investigate the relative absorbed dose with different distances in respective tissue phantom and also in vacuum phantom with 5 cm distance.
Tissue basis density table
ResultsResults
Energy fluence vs. SpectrumEnergy fluence vs. Spectrum
Calculated Calculated 6060Co fluence dataCo fluence data (MeV-1 cm-2)(MeV-1 cm-2)
Calculated Calculated 6060Co fluence dataCo fluence data (MeV-1 cm-2)(MeV-1 cm-2)
Calculated Calculated 6060Co fluence dataCo fluence data (MeV-1 cm-2)(MeV-1 cm-2)
Air-kerma strengthAir-kerma strength
Article Air-kerma strengthPer unit source activity
(cGy.cm2.h-1.Bq-1 )This work 3.035×10-7 ±0.15%
T. Palani Selvam et al.(2010), India
3.04×10-7 ±0.05%
Dose Rate ConstantDose Rate Constant
Article Dose rate constant, Λ(cGy h-1 U-1)
This work 1.097 1.097 ± 0.12%± 0.12%
T. Palani Selvam et al.(2010), India
1.086 1.086 ± 0.06%± 0.06%
Tissue basis relative absorbed doseTissue basis relative absorbed dose
Relative absorbed dose with distanceRelative absorbed dose with distance
Lung
Comp. bone
Conclusion
In the calculation of air-kerma strength and dose rate constant, uncertainty were 0.15% and 0.12% which is acceptable limit.
Published data of Palani Selvam, the uncertainty were 0.05% and 0.06% which are lower than our values.
In this study, EGSnrc Monte Carlo code was used but Palani Selvam used MCNP code
Relative absorbed dose in different tissues in 5 cm distance are approximately same accept lung tissue. 22% less dose in lung tissue with water
The relative absorbed dose with different distances in respective tissue phantom, the lung doses are higher than the compact bone
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