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Information and examples on FLUKA Monte Carlo simulations

FLUKA wiki page for UoB Medphysmc. The purpose of this wiki is to provide information for students and employees at the University of Bergen interested in the field of particle therapy, i.e., radiation therapy with protons and heavier ions. This page contains information on ongoing and previous projects on particle therapy at IFT.

For the majority of our projects on particle therapy we use the Monte Carlo simulation code FLUKA, either as the main tool, or to support the project. Several projects are based on clinical treatment plans which we recalculate in FLUKA to enable more accurate estimates of dose, and to apply various models for biological dose/response based on physical quantities such as absorbed dose and Linear Energy Transfer.


Introduction to FLUKA

FLUKA is a general purpose Monte Carlo code and is used for a number of applications in experimental physics, dosimetry, detector design, medical physics and radio-biology.

Flair and Flair-Geoeditor

Flair is the Graphical user interface for FLUKA and is used for preparing the simulation as well as running the simulations, process and plot the data (through Gnuplot). Flair also contain a geometry viewer/editor named flair-geoviewer, which is used for visualization and editing of the simulation geometry.

The Flair-Geoeditor

The Flair-Geoeditor (previously geoviewer) can be used for visualization and edition of the geometry. Several tutorials are available on youtube. See e.g. this tutorial on selection of regions and zones.

Installation and running


In order to install FLUKA you must, as a registered user, download the necessary software from the FLUKA web-page. At the University of Bergen we use Ubuntu and the 64bit Gfortran version of FLUKA, and this is what we recommend for new users at the university. If you wish to use a Windows-pc you can download FLUPIX. FLUPIX is Linux Live CD, with pre-installed FLUKA, flair and all the necessary tools in for performing fluka runs. In the packages.txt you will find a complete list of the packages currently included in the ISO image. To save disk space, FLUPIX is only able to run through the VirtualBox machine (www.virtualbox.org) a free and open source Virtual machine supported by Sun. More information on FLUPIX can be found here.

If you wish to install FLUKA, Flair and Flair-Geoviewer yourself, you can find a detailed installation guide here

Lectures, presentations and exercises

The best way to learn FLUKA is to attend one of the courses held by the FLUKA-team. If this is not an immediate option you can find a large number of lectures and exercises from both basic courses and advanced courses on the FLUKA web-page. Lectures and exercises from one of the beginners courses are available here.

Available Master's Thesis projects and topics

A broad range of topics within particle therapy are available for Master's studies at IFT. You may find some of them (but far from a complete list)

Oxygen effect - Oxygen enhancement ratio - in proton therapy

Difference in Relative biological effectiveness of passive scattering - and intensity modulated proton therapy

Phenomenological models for the Relative biological effectiveness in proton therapy - on the impact of cell-irradiation design

Monte Carlo simulations of neutron based in vivo range verification in proton/particle therapy

This aim of this project (which is available for new students) is to exploit secondary particles produced during particle therapy to verify the correctness of the treatment, i.e. that the dose to the patient was delivered as planning. This will be done by detecting secondary neutrons (using Monte Carlo simulations) and from the distribution of these, try to calculate the range and dose from the primary beam. A more detailed project description can be found here.

Local FLUKA projects


Sensitivity study of the microdosimetric kinetic model parameters for carbon ion radiotherapy

Dahle, Tordis et al. Physics in Medicine and Biology (2018)

The relative biological effectiveness (RBE) calculation methods currently applied clinically in carbon ion therapy are derived from the microdosimetric kinetic model (MKM) in Japan and the local effect model (LEM) in Europe. The input parameters of these models are based on fit to experimental data subjected to uncertainties. We therefore performed a sensitivity study of the MKM input parameters, i.e. the domain radius (rd), the nucleus radius (Rn) and the parameters of the linear quadratic model (αx and β).

The article is available in pdf format here.

Exploration and application of phenomenological RBE models for proton therapy

Rørvik, Eivind et al. Physics in Medicine and Biology (2018)

The relative biological effectiveness (RBE) of protons varies with multiple physical and biological factors. Phenomenological RBE models have been developed to include such factors in the estimation of a variable RBE, in contrast to the clinically applied constant RBE of 1.1. In this study, eleven published phenomenological RBE models and two plan-based models were explored and applied to simulated patient cases.

The article is available in pdf format here.

Optmization of proton therapy plans with respect to biological and physical dose distributions - Master thesis by Helge Henjum

Proton therapy is a radiation treatment method growing around the world. This is mainly due to the protons ability to deposit dose more conformal compared to conventional photon therapy. Protons also differ in terms of biological effect compared to photons for the same physical dose. To account for this increased relative biological effectiveness (RBE), a constant RBE of 1.1 is applied in clinical proton therapy treatment planning, i.e. approximately 10% lower physical dose is given to the tumor if proton therapy is used. It is however known that the RBE is not constant, and is dependent on e.g. the linear energy transfer (LET), physical dose and tissue type. By using biological optimization the tumor may get a homogeneous biological dose distribution, and prevent over- and under dosage to healthy tissue and the tumor volume. Variable RBE models can be used to optimize a treatment plan with respect to RBE-weighted dose, but these are not yet available in commercial treatment planning systems.

The aim of this study was to implement a method for optimization of treatment plans with respect to both biological and physical dose, and further use this to analyze the differences in physical and biological dose distributions depending on the optimization strategies applied.

The thesis is available in pdf format here.


A phenomenological biological dose model for proton therapy based on linear energy transfer spectra

Rørvik, Eivind et al. Medical Physics (2017)

The relative biological effectiveness (RBE) of protons varies with the radiation quality, quantified by the linear energy transfer (LET). Most phenomenological models employ a linear dependency of the dose-averaged LET (LETd) to calculate the biological dose. However, several experiments have indicated a possible non-linear trend. Our aim was to investigate if biological dose models including non-linear LET dependencies should be considered, by introducing a LET spectrum based dose model.

The article is available in pdf format here.

Monte Carlo based comparison of constant vs. variable RBE for proton therapy patients - Master thesis by Johan Martin Søbstad

The primary objective of this project was to calculate and compare the dose-to-patient results of constant RBE versus variable RBE calculated by different models for protons. The calculations were done by a combination of FLUKA Monte Carlo (MC) simulations and post-processing using custom scrips written in Python. CT images and treatment plan information for a medulloblastoma patient was imported into FLUKA, where the dose and linear energy transfer (LET) was calculated. The RBE values were subsequently calculated for four different models, assuming constant tissue parameters. An in-depth investigation of the different model properties was performed by systematically varying the model parameters. RBE calculations with a simple treatment plan on a water phantom were also performed.

The thesis is available in pdf format here.

Monte Carlo simulations of neutron doses from pencil beam scanning proton therapy - Master thesis by Yannick Alexander Broese van Groenou

A side effect of proton therapy is the production of secondary neutrons generated by the beam particles through nuclear interactions. Neutrons contribute with an unwanted, additional dose, and because neutrons are highly penetrating, they can reach organs and tissue far outside the treatment field. As these particles can have a very strong biological impact, a small dose can lead to a high risk of radiation-induced cancer and other secondary malignancies. In this thesis, a cranio-spinal irradiation treatment using intensity-modulated proton therapy for a pediatric medulloblastoma patient was simulated by using the Monte Carlo simulation code FLUKA. Two obliquely opposed proton beams with energies 175 – 190 MeV were used for the cranial fields, and 135 – 150 MeV proton beams for the spinal fields. The therapeutic biological proton dose was 23.4 Gy(RBE). The neutron absorbed dose and ambient dose equivalent were scored for organs at risk and the PTVs. In the treatment, organs at risk were thyroid, liver, colon, stomach, lung, kidneys, bone and bladder. The dose distributions were plotted in a dose-volume histogram, visualized in two-dimensional plots and one-dimensional graphs of dose as a function of depth inside the patient.

The thesis is available in pdf format here.

Linear energy transfer distributions in the brainstem depending on tumour location in intensity-modulated proton therapy of paediatric cancer

Fjæra, Lars Fredrik, et al. Acta Oncologica (2017)

For tumours near organs at risk, there is concern about unintended increase in biological dose from elevated linear energy transfer (LET) at the distal end of treatment fields. The objective of this study was therefore to investigate how different paediatric posterior fossa tumour locations impact LET and biological dose to the brainstem during intensity-modulated proton therapy (IMPT).

The article is available in pdf format here.

The FLUKA Monte Carlo code coupled with the NIRS approach for clinical dose calculations in carbon ion therapy

Magro, Giuseppe et al. Physics in Medicine and Biology (2017)

In this paper, we describe the coupling of the NIRS (National Institute for Radiological Sciences, Japan) clinical dose to the FLUKA MC code. We moved from the implementation of the model itself to its application in clinical cases, according to the NIRS approach, where a scaling factor is introduced to rescale the (carbon-equivalent) biological dose to a clinical dose level. A high level of agreement was found with published data by exploring a range of values for the MKM input parameters, while some differences were registered in forward recalculations of NIRS patient plans, mainly attributable to differences with the analytical TPS dose engine (taken as reference) in describing the mixed radiation field (lateral spread and fragmentation). We presented a tool which is being used at the Italian National Center for Oncological Hadrontherapy to support the comparison study between the NIRS clinical dose level and the LEM dose specification.

The article is available in pdf format here.

Monte Carlo simulations of a low energy proton beamline for radiobiological experiments

Dahle, Tordis J., et al. Acta Oncologica (2017)

In this study, we characterized and explored a novel low energy proton beam cell irradiation setup through dosimetry and dedicated MC simulations. Such low energy proton beams are ideal for radiobiological experiments, since low energy proton beams can produce high LETd values and narrow LET spectra. The objective of this study was to determine the initial beam parameters for MC simulations of the novel cell irradiation setup, and further use MC simulations to determine spatial variations in LET in positions intended for cell irradiation. We further compared LET values from our proton beam to LET values from an 80 MeV proton beam, representing a typical minimum energy, and thus maximum LETd, available at clinical facilities.

The article is available in pdf format here.

The workflow for dose verification with FLUKA. The custom made scripts (green boxes) enable dose recalculation in FLUKA and comparison to the original dose distribution. Treatment plans (DICOM format) from the TPS are run through the scripts which obtain relevant parameters and information required by FLUKA. Figure: Lars Fredrik Fjæra


Development of a Monte Carlo Based Treatment Planning Verification Tool for Particle Therapy - Master thesis by Lars Fredrik Fjæra 

In this project, a tool that translates treatment plan information into data readable for the FLUKA code was developed. The tool includes several routines based on Python scripts. It enables reading of relevant treatment plan settings required to automatically generate a FLUKA simulation file for dose recalculation. Functions for data analysis and visualization, as well as comparison between the TPS and FLUKA results were also created. In addition, scripts for converting a FLUKA calculated dose distribution into DICOM format were created.

The thesis is available in pdf format here.


A Comparative Study of Radiation Environment and Secondary Dose Production in a Particle Therapy Treatment Room Applying Proton, Helium and Carbon Ion Beams - Master thesis by Jarle Rambo Sølie

The purpose of this master thesis has been to perform a comparative study of the induced radiation environment inside a typical treatment room during irradiation of a water phantom with proton, helium and carbon beams, and introduce various entrance structures and shielding materials to the treatment room in order to compare and illuminate their effects and study the differential fluence spectra of neutrons and photons entering and exiting these featured structures. Water equivalent worker phantoms representing hospital personnel were placed inside and outside the vicinity of the entrance structures and effective dose to each of them were scored. A total of 24 simulations covering eight different treatment room layouts were performed in FLUKA and the final results illuminated the many considerations and deliberations that must be taken into account during the planning, building and shielding fitting of a treatment room for use in particle therapy.

The thesis is available in pdf format here.

The Influence of the Energy Degrader Material for a Therapeutical Proton Beam - Master thesis work by John Alfred Brennseter

In cyclotron based proton therapy an energy degrader is needed to modulate the proton beam energy. The proton beamenergy decides the range of the particles and thereby where the dose is imparted. The influence of the material of the energy degrader for a 250 MeV therapeutic proton beam has been evaluated with FLUKA, a Monte Carlo based particle transport software. A geometry of a double wedge degrader of beryllium, carbon or lexan and a collimator of copper and carbon has been used. The momentum spread, angular spread, transmission fraction neutron yield and photon yield have been measured.

The thesis is available in pdf format here.

A Comparison of Biological Dose Estimates in Proton and Carbon Ion Therapy Based on Averaged and Full Linear Energy Transfer Spectra - Master thesis work by Eivind Rørvik

Radiotherapy with ions, also known as particle therapy, is increasing rapidly. To adapt from the higher biological effectiveness of particles compared to photons, the concept of relative biological effectiveness (RBE) is used. Protons are slightly more effective than photons, and the RBE is set to be constant 1.1. The constant RBE value is not a physical property of the beam, it is simply assigned to be 1.1 by a consensus in the scientifc community. Experiments indicate that the RBE in reality is marginally increasing along with the treatment depth. For carbon ions the variations in RBE are signifcantly higher and typically range between 1 and 3. The variation is taken into account in treatment planning, however, relatively large uncertainties are present in the radiobiological models applied. Many of these models are based on correlations between the calculated linear energy transfer (LET) and experimentally measured RBE. Most phenomenological models are based on the dose averaged LET, LETd. However, it should also be possible to correlate the biological effect to the full dose weighted LET spectrum, d(L). By using a biological weighting function (BWF), it is possible to estimate the RBE from either LETd or d(L). In this work, several proton and carbon ion beams were simulated with the FLUKA Monte Carlo code. The physical absorbed dose and the LET spectrum d(L) were estimated at different depths in a water phantom. A BWF was created upon existing cell experiments databases and applied to quantify the effect of the averaging.

The thesis is available in pdf format here.


Dosimetric Consequences of Dropping the Momentum Analysis System in a Compact Proton Therapy System - Project thesis by Eivind Rørvik

The high investment cost of proton therapy centers could be lowered by building just one single room systems. When a accelerator serves a single treatment room, the beam line could be minimized to cut the cost further. One of the systems available on the market today is cutting the Momentum Analysis system (MAS, Momentum analyser), and degrading the beam directely in front of the patient. The momentum of the beam is then larger compared to other systems, which further enlarges the distal dose falloff, a common dosimetric parameter used in clinics. A higher distal dose falloff will create a higher dose to organs at risk behind the tumor volume, which enlarges the NTCP, as shown in the figure.

In this thesis a simplified 250 MEV proton beam is degraded through PMMA and dropped into a water phantom. The thickness of PMMA is varied to get different clinical relevant ranges. Other proton beams were dropped directly into the water phantom, with realistic ESS/Synchrotron parameters. The bragg curves of the beams were recorded by a usrbin-card in FLUKA, and the range (90%) and distal dose falloff (80%-20%) were analysed by a matlab script. The plot shows the 5 different beams.

As seen, the systems without a momentum analyser have a constant distal dose falloff for all ranges, compared to the ESS/synchrotron systems, which have an almost proportional ratio between the parameters.

At deep treatment depths (prostate etc.), the clinically differences between the systems nearly negligible. But for shallow treatment depths (Breast, spine etc), the should be accounted for. For some conditions, as left sided breast cancer, treatment with such a system MIGHT not be favoured over high precision photon therapy. Multiple dose plans should be made and compared for these potential cancer type, to either confirm or rule out the possible dosimetric consequence of dropping the MAS.

The thesis was written in a project course at NTNU under supervision of Pål Erik Goa, in collaboration with Kristian Smeland Ytre-Hauge.


Fluka input file (change from .txt to .inp)

Flair file

Project report

Simulations of Neutron Fluence Through Concrete Wall in Proton Therapy - Project thesis by John Alfred Brennsæter

In proton therapy secondary particles are generated when the protons interact with matter. As the protons have larger energy than photons in conventional radiation therapy, there are generated neutrons with higher energy. This leads to that thick walls are needed to keep the neutron radiation from the treatment room away from the surroundings.

In this thesis proton beams with varying energy from 70 - 250 MeV have been dumped in a water phantom of (100x30x40)cm3 . The neutron fluence was recorded by the usrbin-card, and the energy spectrum was recorded by the usrbdx-card.

This simulations show that the penetration depths of neutrons are increasing with increasing proton beam energy.

The thesis was written in a project course at NTNU under supervision of Pål Erik Goa, in collaboration with Kristian Smeland Ytre-Hauge.


Fluka input file (change from .txt to .inp )

Flair file

Project report

Extremely high-granularity digital tracking calorimeter for the detection of scattered protons in proton computed tomography - Master thesis by Daniel Aadnevik

The ability to accurately position the Bragg peak at a planned location is a major advantage of protons and light ions, but incomplete knowledge about the tissue properties and their relative position limits the treatment precision, and range uncertainties of several millimeters may arise. This occurs when photon attenuation maps from computed tomography (CT) scans are converted into relative stopping power. The principles of a proton CT scanner as an alternative to X-ray CT will be outlined in this thesis. Imaging with protons allows direct information about the stopping power to be obtained, and has the potential to reduce range uncertainties from current values of 3-10 mm to 1-3 mm.

A simplified model of the FoCal detector has been implemented in the Monte Carlo simulation package FLUKA, and the detector response to a 180 MeV - 280 MeV proton beam has been studied. Results on the tracking precision was found to be comparable to existing prototypes, but the thickness of the absorbers was found to limit the ability to accurately determine the Bragg peak position. The result of replacing the absorbers with a lighter material resulted in an improved tracking resolution, and an alternative detector construction optimized for proton CT will be presented. The ultimate goal is to measure the calorimeter response to a therapeutic proton beam. The aim of this thesis has been to prepare the beam tests, both through Monte Carlo simulations and systematic detector studies.

The thesis is available in pdf format here.


Simulations of a Therapeutic Proton Beam with FLUKA Monte Carlo Code and Varian Eclipse Proton Planning Software - Master thesis work by Kine Johnsen

The purpose of this project has been to apply Monte Carlo software to simulate a proton beam resembling a therapeutic beam, and to study the interactions of this beam in phantoms of various design.

The Monte Carlo simulations were compared to results from Eclipse (a clinical dose planning system). The overall agreement between the two calculation methods were adequate, especially with respect to dose coverage within the defined target volume. However, when introducing different materials such as bone, air and aluminium into the geometry, the differences between the two methods became apparent and it illustrates the tentative limitations of a fast, clinical optimized, dose planning tool compared with a more accurate and detailed, hence tentatively slower, Monte Carlo simulation tool.

Kine looked into the source.f user routine in FLUKA in order to be able to define more complex beams than a simple pencil beam. Some example files for creating Spread-Out-Bragg-Peaks for protons and Fluka input files are available here: source_kine.f

The thesis is available in pdf format here.

Measurements and Monte Carlo Simulations of Neutron Doses from Radiation Therapy with Photons, Protons and Carbon Ions - Ph.D. thesis by Kristian Smeland Ytre-Hauge

The overall objective of this thesis has been to investigate the magnitude and distribution of neutron dose from radiation therapy with photons, protons and carbon ions. The pursuit of this ambition has also required an extensive study of the applied neutron detectors’ properties. Measurements in proton and carbon ion beams were performed with a novel neutron detector based on radiation effects in Static Random Access Memory (SRAM) chips. For measurements of neutron dose in photon therapy, bubble detectors and thermoluminescence detectors (TLDs) were applied. Monte Carlo simulations with the FLUKA Monte Carlo simulation package were conducted for comparison with the experimental data.

The thesis is available in pdf format here.

Biasing exercise from Workshop