Warning, /geant4/examples/extended/medical/radiobiology/README is written in an unsupported language. File is not indexed.
0001
0002
0003 HEAD
0004
0005 =========================================================
0006 Geant4 - an Object-Oriented Toolkit for Simulation in HEP
0007 =========================================================
0008
0009 radiobiology
0010 ------------
0011
0012
0013 Radiobiology is an application realized for dosimetric and radiobiological applications of proton and ion beams. Specific tools were built to evaluate primaries and secondary energy spectra and a set of classes, dedicated to the computation of biological, as LET (Linear Energy Transfer), RBE (Relative Biological Effectiveness), Survival Fraction, and physical (as dose and fluence) quantities were implemented.
0014
0015 1- GEOMETRY DEFINITION
0016
0017 The physical and dosimetric quantities are calculated in the water tank by scoring every quantity in each of the slices, representing a customizable (in terms of dimensions and materials) volume that can be voxelized depending on the user's needs.
0018
0019 In the proposed example, the “default” water tank represents a phantom typically used in the clinical hadrontherapy practice, to reconstruct the dose profile distributions in water .
0020 The phantom has a standard dimension of 4 x 4 x 4 cm and was sectioned into 0.2 x 40 x 40 mm slices (See Figure 1). The voxel dimensions can be user defined and can vary from 1um to 1 mm
0021 The source is positioned on one of the faces of the box
0022
0023 The defaultMacro.mac uses the default geometry configuration mentioned above with a simple run of 100k protons with a Gaussian energy distribution with a mean of 62 MeV and a standard deviation of 0.65 MeV
0024 The visualize.mac just creates a teest geometry and opens visualization
0025
0026 2- PHYSICS LIST
0027
0028 In Radiobiology it is possible to activate three physics lists that are those already recommended for medical physics applications and that cover all the physics processes needed for a correct simulation in this field.
0029
0030 The electromagnetic interactions are modeled using the G4EmStandardPhysics_option4 constructor, which uses a condensed history algorithm based on the Beth-Bloch energy loss formula. This physics constructor was created for applications requiring high accuracy in electron, hadron, and ion tracking. It contains the most accurate standard and low-energy models and is recommended for simulations focused on medical physics applications.
0031 The hadronic interactions are simulated using models implemented in the QGSP BIC and QGSP BIC HP constructors, which employ Geant4 native preequilibrium and de-excitation models as low energy stages of the Binary Cascade model for protons, neutrons, and ions. The QGSP BIC HP constructor uses, in addition, the high precision neutron package (ParticleHP) to transport neutrons and light-charged particles with energiesfrom 20 MeV down to thermal energy.
0032
0033 Production cuts for secondary generation are an important element in any MC simulation. It has a significant impact on energy deposition, particularly when small quantities are examined. The production cut in Geant4 is a distance (given in units of length), and secondary particles (electrons, positrons, gammas, and secondary protons) are only monitored if their expected range in that medium is greater than the imposed cut. Otherwise, secondary energy is not tracked and is deposited in the secondary production position. The cut for this example is achieved through the standard Geant4 implementation.
0034 /run/setCutForAGivenParticle e- 0.1 mm
0035 /run/setCutForAGivenParticle e+ 0.1 mm
0036 /run/setCutForAGivenParticle proton 0.1 mm
0037
0038 3- LET CALCULATION
0039
0040 Radiobiology simulates and calculates the averaged LET-dose and LET-track fully accounting for the contribution of secondary particles generated in the target fragmentation
0041 Dependencies as respect to the transport parameters adopted during the Monte Carlo simulations as the production cut of secondaries particles, voxel size and the maximum steps length are minimized in the LET calculation.
0042 At run time, data needed to calculate LET are collected. At the end of simulation, LET mean values are calculated and stored into a file.
0043
0044 The Let.out file will be produced at the end of a run, where you can
0045 find the dose and track average LET for each tracked particles (both primary and
0046 secondary ones) and the total mean LET.
0047
0048 The file is structured as follows:
0049 - The first three columns contain the voxel indexes (first index "i" refers to the beam direction);
0050 - The fourth and fifth columns contain respectively total mean dose LET (LDT) and total mean track LET (LTT)
0051 - The rest of columns contain LET Dose and Track for each single ion (whose name is in the top row of the file).
0052
0053 4- RBE and Survival calculation
0054
0055 A method was developed to assess the biological damages produced by proton and ion beams in terms of survival fraction curves, i.e of the number of cells able to survive after the irradiation at different dose. The approach is based on the combined use of Monte Carlo Geant4 simulations (to calculate the doses deposited and the energy spectra of particles interacting with cells) and of the Survival analytical code (Manganaro L, Russo G, et al. Survival: a simulation toolkit introducing a modular approach for radiobiological evaluations in ion beam therapy. Phys. Med. Biol. 2018;63(8). 08–01).
0056 The Monte Carlo simulations permit the calculation of the Edep and Ekin distributions that, coupled with the radiobiological response model, allow the final and calculation of a survival curve.
0057 The kinetic energy and the LET value of any primary ion and of the secondaries generated in each slice of the simulated water phantom are retrieved at each simulation step. The corresponding values of αi and βi, for each specific ion i with a kinetic energy Ei and a released dose Di, are then calculated by direct linear interpolation of the Look-up-tables provided by the Survival analytical code.
0058 (G.Petringa et al., Physica Medica 58 (2019) 72–80)
0059
0060 The AlphaAndBeta.out and RBE.out files are produced at the end of the run.
0061 AlphaAndBeta.out contains the average alpha (first column) and beta (second column) parameters calculated for each slice (third column).
0062
0063 RBE.out contains the following quantities:
0064 Dose (Gy): the physical dose;
0065 ln(S): the natural log of the Survival Fraction;
0066 Survival Fraction;
0067 DoseB (Gy): the biological dose;
0068 RBE: relative biological effectiveness;
0069 depth (slice): n. of the slice;
0070
0071
