Attention
Attention
Chemical Scorers
Chemical scorers are those that utilize either the Step-By-Step (SBS) or the Independent Reaction Times (IRT) algorithms to simulate the diffusion and reaction of chemical species. TOPAS-nBio provides six chemical scorers, two for SBS and four for IRT. These scorers are:
Scorer Type |
Scorer Quantity |
|---|---|
SBS |
TsSBSGValue |
TsSBSMoleculesAtTime |
|
IRT |
TsIRTGvalue |
TsIRTInterTrack |
|
TsIRTInterPulse |
|
TsIRTStrandBreaks |
Chemical scorers provide a way to terminate the tracks based on total primary energy loss, total primary track length or number of primary particle steps. This is implemented as both, a way to control the particle track size for more control of the G-values, and as a way to reduce the total number of chemical species produced by a certain particle track.
Step-By-Step Scorers
SBS GValues
The Step-By-Step G-Values scorer was the first chemical scorer available since the first release of
TOPAS-nBio. It remained the same from its previous versions, however the naming convention was changed
in order to fall in line with the rest of the chemical scorers. The TOPAS-nBio parameter name for this scorer
component changed from GValue to TsSBSGValue. An example of the usage of this scorer can be found at
/examples/scorers/TsSBSGValues/ with TOPAS-nBio defined reactions GvalueRevisedPhysicsChemistry.txt and
Geant4-DNA default reactions GvalueG4DNADefault.txt. The parameters to setup this scorer are:
# The times at which to report the GValues
dv:Sc/SSBGvalue/TimeToRecord = 7 1 10 100 1e3 1e4 1e5 1e6 ps
And the following particle track kill options:
# Total Energy Loss to Kill the primary track
d:Sc/SSBGvalue/KillPrimaryIfEnergyLossExceeds = 10 eV
# Total energy loss by the primary particle after which the track will be aborted
# and no chemistry will be conducted
d:Sc/SSBGvalue/AbortEventIfPrimaryEnergyLossExceeds = 100 eV
# Total track length to kill the primary track
d:Sc/SSBGvalue/KillPrimaryBasedOnTrackLength = 1 um
The rest of the parameters will be handled by the Ch chemistry parameters. Most of the chemical scorers
share the same particle track kill options. This scorer has been used to calculate G-values with relatively
good agreement as published in [Ramos-Méndez2018].
Number of Molecules At Time
The TsSBSMoleculesAtTime scorer is a way to obtain the total number of a chemical species instead of
its G-value (species per 100 eV of energy deposit). It shares the same particle track kill options from the
TsSBSGValue scorer. An example of such scorer can be found in the folder examples/scorers/TsSBSMoleculesAtTime/,
with the file name TsSpeciesAtTime.txt. Instead of providing the explicit
time values to report G-values from the TsSBSGValue scorer, an automatic binning is provided by using
the following four parameters:
# Number of time bins
d:Sc/MoleculesAtTime/TimeBins = 100
# The lower time limit
d:Sc/MoleculesAtTime/TimeBinMin = 1 ps
# The upper time limit
d:Sc/MoleculesAtTime/TimeBinMax = 1e6 ps
# True for logarithmic binning, false for linear binning
b:Sc/MoleculesAtTime/TimeBinLog = "True"
Independent Reaction Times Scorers
IRT GValues
The TsIRTGValue scorer is the IRT version of TsSBSGValue. The necessary parameters to setup the
scorer are similar to those from the TsSBSMoleculesAtTime scorer. Alongside the particle track kill
options the parameters are:
# Scorer Cutoff time
d:Sc/IRTGValue/CutoffTime = 1 us
# Optional: if it exists the regular track kill options are ignored: Defaults to 0
i:Sc/IRTGValue/MaximumNumberOfSteps = 1e6
# Report DeltaG Values: Defaults to false
b:Sc/IRTGValue/ReportDeltaGValues = "True"
DeltaG values are an optional part of this scorer, they report the number of times a certain reaction
is performed during the simulation per 100 eV of energy deposit (same units as the G-values). The output
file of the DeltaG values will have the same name from the OutputFile parameter from the scorer with a _DeltaG.phsp added at the end.
Apart from this parameters, all IRT scorers take additional parameters from the /procesess/TsIRT.cc
file in order to create the time bins to report the G-values:
# The lower bin limit
d:Sc/IRTGValue/TimeLower = 1 ps
# The upper bin limit
d:Sc/IRTGValue/TimeUpper = 1 us
# The number of Logarithmic bins
i:Sc/IRTGValue/TimeBins = 100
# Use High Time Scavenger: Defaults to False
b:Sc/IRTGValue/HighTimeScavenger = "False"
The TimeLower, TimeUpper and TimeBins are optional and defaults to the values shown here.
The HighTimeScavenger parameter is used to limit the scavenging reaction to 1 micro second, this is done to avoid long simulation times between cycling reactions of the form:
ReactantA + ScavengerA = ReactantB
ReactantB + ScavengerB = ReactantA
By having this limiter, no type VI reaction will be performed after 1 micro second. However some applications may depend on higher simulations times with the need of special scavengers like the Fricke dosimeter in which case users can opt to remove this limiter.
An example of the usage of this scorer can be found at /examples/scorers/TsIRTGvalue/TsIRTGvalue.txt. TOPAS-nBio
IRT simulations accuracy has been reported in [Ramos-Méndez2021]. The Fricke dosimeter has been
implemented alongside a way to automatically change reaction times by pH as explained in Independent Reaction Times,
the /examples/scorers/TsFricke/FrickeIRT.txt example shows the implementation of the results published in [Ramos-Méndez2020].
IRT GValues Inter-Track
TOPAS-nBio allows users to quantify the effect of multiple particle tracks on chemical yields, in what is known as inter track effects. These effects don’t appear unless two or more tracks happen to interact with the medium in close proximity considering both the space and the time of ionization and excitation of the medium. Specifically speaking, two particle tracks must happen with a time separation of at least 1 micro second and a separation of a few tens of nano meters apart.
The TsIRTInterTrack scorer was made to quantify this effect on a track-by-track basis. It allows the use of
as many tracks as the user specifies distributed in the space and time which the user can manually specify with:
# Set to True to allow multiple tracks per IRT run: Defaults to False
b:Sc/IRTGValuesIT/UseMultipleTracks = "True"
# Set the individual time at which each track hits the scorer
dv:Sc/IRTGValuesIT/TimeDelay = 5 1 2 2 5 1e3 ps
# Set the spatial offset of each track per IRT run.
dv:Sc/IRTGValuesIT/SpatialOffsetX = 0 1 0 5 10 nm
dv:Sc/IRTGValuesIT/SpatialOffsetY = 0 1 1 50 20 nm
dv:Sc/IRTGValuesIT/SpatialOffsetZ = 0 1 1 0 10 nm
An example of this scorer can be found at /examples/scorers/TsInterTrack/TsIRTInterTrack.txt. Using this scorer
it is possible to recreate the results reported in [Kreipl2009].
IRT GValues Inter-Pulse
Experimentally, determining a track-by-track inter-track effect is not available, instead we rely on the use of a pulsed irradiation.
By using pulsed irradiation, high radiation dose rates can be achieved in what is called FLASH irradiation.
TOPAS-nBio includes a scorer that allows to simulate inter track effects called TsIRTInterPulse. This scorer was used in the paper
[Ramos-Méndez2020]. It completely removes the particle track kill options while providing additional options for the
pulse distributions with the parameters:
# Total Dose used per IRT run
d:Sc/IRTCummulative/PrescribedDose = 5 Gy
# The Pulse Distribution can be:
# "Gaussian", "Uniform", "None", "Discrete" and "Exponential"
s:Sc/IRTCummulative/PulseDistribution = "Gaussian"
# Pulses to use, dose will be distributed among them: Defaults to 1
i:Sc/IRTCummulative/NumberOfPulses = 5
# Number of Pulses per unit time
d:Sc/IRTCummulative/PulsesFrequency = 1e6 /s
If the pulses are “Gaussian” or “Uniform” the following parameters must be set:
# The mean time of the pulse
d:Sc/IRTCummulative/PulseTimeMean = 1 us
# The average duration of the pulse by using the FWHM
d:Sc/IRTCummulative/PulseFWHM = 2 us
If the pulses are “Discrete”, the following parameters are needed:
dv:Sc/IRTCummulative/TimeValues = 5 1 1.5 2 2.5 5 us
uv:Sc/IRTCummulative/TimeWeights = 5 0.1 0.25 0.05 0.25 0.35
If the pulses are “Exponential” only the mean time of the pulse is needed with:
d:Sc/IRTCummulative/PulseTimeMean = 1 us
Chemical simulations always start at 1 pico second, taking into account the physical and pre-chemical stages. Due to the behaviour of the time sampling when using pulse distributions it is possible to have chemical species created and diffusing before the chemical stage. To avoid this, users can use the following parameter:
b:Sc/IRTCummulative/ForceLowTimeCutTo1ps = True
The default value of this parameter is False.
TOPAS-nBio provides an example of this scorer in /examples/scorers/TsIRTCummulative/TsIRTCummulative.txt.
The effect of FLASH radiation on chemical yields using this scorer in TOPAS-nBio was published [Ramos-Méndez2020], for more information regarding the expected results and details about FLASH please refer to this paper.
Note
The user must take care to not overload the IRT of TOPAS-nBio by sending either a high number of pulses or a high dose, otherwise this scorer may consume all the memory available, causing the computer to freeze or crash, user discretion is advised.
IRT DNA Strand Breaks
Both the SBS and IRT scorers can be used for DNA strand break simulations. The specific implementation of such simulations
can be very complex depending on the reaction-diffusion algorithm. TOPAS-nBio provides a way to simulate DNA strand
breaks in plasmid DNA using the IRT method. In order to properly run plasmid DNA strand break simulations, the user must perform
some pre-simulation setup either by hand or by using the IRT Supercoiled Plasmid Setup provided in the TOPAS-nBio code.
The TsIRTStrandBreaks scorer assumes the user has already performed the necessary steps and has the necessary files to properly
score de DNA strand breaks by using:
d:Sc/DNAStrandBreak/PrescribedDose = 50 Gy
s:Sc/DNAStrandBreak/InputFile = "pUC19_Plasmids.xyz"
iv:Sc/DNAStrandBreak/OnlyUseDNAMoleculesWithID = 1 104
Where the InputFile refers to the file containing the position of the DNA molecules. OnlyUseDNAMoleculesWithID
allows to filter DNA molecules prior to entering the IRT simulation and save time. An example of this scorer can be found at
/examples/scorers/TsScoreDNADamage/PlasmidIrradiation/TsScoreDNADamage.txt. For more information regarding the
performance and setup of this example, see [Ramos-Méndez2021].
This scorer will produce three different files, a phsp file with the number of molecules at a given time of the simulation,
a header file for this file and a .dnadamage file. The .dnadamage file contains the Base Pair ID and Strand ID of
each break. It is up to the user to work around this information to obtain the number of Single Strand Breaks and Double Strand Breaks.
The Base Pair ID will be a number between 1 and the number of plasmids multiplied by the number of base pair per plasmid.
The user will need to obtain the Plasmid ID by dividing the Base Pair ID by the number of base pairs of the specific
plasmid used.
Note
It is important to mention that this scorer is not Multithread compatible and must be used with a thread number of 1. Future releases may address this limitation.
Note
Other DNA damage scorers are available and are compatible with the SBS method, see the appropriate sections in this documentation for more detail.
References
- Ramos-Méndez2018
Ramos-Méndez J, Perl J, Schuemann J, McNamara A, Paganetti H, Faddegon B 2018. Monte Carlo simulation of chemistry following radiolysis with TOPAS-nBio. Physics in Medicine and Biology, 63(10), 0–12. https://doi.org/10.1088/1361-6560/aac04c
- Kreipl2009
Kreipl M S, Friedland W, Paretzke H G 2009. Time- and space-resolved Monte Carlo study of water radiolysis for photon, electron and ion irradiation. Radiation and Environmental Biophysics, 48(1), 11–20. https://doi.org/10.1007/s00411-008-0194-8
- Ramos-Méndez2020(1,2,3)
Ramos-Méndez J, Domínguez-Kondo N, Schuemann J, McNamara A, Moreno-Barbosa E, Faddegon B 2020. LET-dependent intertrack yields in proton irradiation at ultra-high dose rates relevant for FLASH therapy. Radiation Research, 194(4), 351–362. https://doi.org/10.1667/RADE-20-00084.1
- Ramos-Méndez2021(1,2)
Ramos-Mendez J A, LaVerne J A, Domínguez-Kondo J N, Milligan J, Stepan V, Stefanová K, Perrot Y, Villagrasa C, Shin W-G, Incerti S, McNamara A L, Paganetti H, Perl J, Schuemann J, Faddegon B 2021. TOPAS-nBio validation for simulating water radiolysis and DNA damage under low-LET irradiation. Physics in Medicine; Biology, 66(June), 1–12. https://doi.org/10.1088/1361-6560/ac1f39