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Physics Master Thesis: Tri-chrome model of nuclear scattering in carbon radiation therapy

We offer one physics master thesis positions at RaySearch Laboratories in Stockholm. Three topics are formulated and this announcement describes one of them.

The topic is to implement a model of relative biological effect of carbon irradiation that handles scattering of hydrogen, helium and heavier nuclei separately (the so-called tri-chrome model). Accurate modelling of the biological effect is important when creating carbon treatment plans, as it allows for better prediction of tumour control and potential side effects.

The model is physics driven using Monte Carlo simulations (FLUKA or Geant4). The prototyping can be done in your language of choice: MATLAB/Python/C++/C#. For evaluation you will have access to RaySearch’s powerful treatment planning software RayStation, the RayStation scripting interface in Python and if time permits also the RayStation development code in C++ and C#. As support you will have your supervisors at RaySearch, the RaySearch crew in general and the physics group at the Development Department particularly.

Background and purpose

Cancer treatment with carbon ions is the most advanced form of radiation therapy. Due to the large size and investment cost for the accelerator facilities, it is currently only available at a few centers around the world. Nearly all of these centers are directly involved in research to evaluate the benefits of carbon ion therapy for the treatment of different tumor types.

Radiation therapy planning is based on accumulated experience on how different tumor types and risk organs respond to irradiation. Most of this experience comes from photon treatments. Tissue irradiated with carbon ions responds stronger to the same delivered physical dose as compared to conventional (photon) radiation therapy. This is expressed as a relative biological effectiveness (RBE) higher than one and RBE-weighted dose is used in the planning process to be able to understand when carbon treatment is particularly beneficial, and to be able to lean on accumulated experience.

The models used to describe this effect take into account the ionization generated both around the primary carbon ion and around the secondary nuclear fragments generated in the patient. In the tri-chrome concept, the radial distribution of the secondary fragments is taken into account explicitly, separating primary carbon and fragments into three components, with heavier fragments closer to and lighter fragments (H, He) further away from the central axis.

The optimal treatment plan for each patient is determined using a treatment planning system (TPS), such as RayStation® by RaySearch Laboratories, where an analytic dose calculation is implemented. This calculation uses input from Monte Carlo particle transport simulations with multi-purpose codes such as FLUKA or Geant4. Currently, these calculations use a one-dimensional (longitudinal) fragment distribution with no radial dependence.

The aim of this project is to study the effect of applying a tri-chrome distribution for the nuclear fragments on the resulting biological effective dose distribution in carbon ion therapy. 

The specific objectives are:

  • To study the physics of analytic and Monte Carlo dose calculations in ion therapy, in particular the distributions of secondary fragments and the tri-chrome model.
  • To simulate and evaluate multi-dimensional fragment spectra distributions using Monte Carlo transport codes.
  • To develop a simple RBE-weighted dose calculation where one-dimensional fragmentation can be compared to the use of tri-chrome.
  • To compare the results of the present implementation with tri-chrome for realistic treatment plans with different biological models.
  • Time permitting, to implement a tri-chrome dose calculation in RaySearch commercial treatment planning system RayStation®.

Education, experience and knowledge

This master thesis is the final part of a master education in physics, engineering physics, medical physics or a similar program, where you have excelled.

You are motivated and intelligent and you like physics analysis, math and programming. You are used to computers and programming, if the experience is less this is compensated by will and skill to learn.

Meriting but by no means required are proven skills in C++/MATLAB/Python, less likely but still meriting is knowledge of C#/.NET. 

Spoken and written English is required, Swedish is highly meriting. 

Personal profile

You have good analytical skills and a problem-solving mindset. When working on a problem, you formulate the right questions, identify what is important and work in a goal-oriented way towards a solution. You are a strong team player who takes responsibility and contributes to a positive atmosphere. You take pride in delivering high-quality results with efficiency. 

About physicists at RaySearch

The physicists at RaySearch are responsible for physics algorithms and functionality for photon, electron, proton and carbon-ion treatments within the treatment planning system RayStation. The physicists participate in all steps of the research and/or development processes, including method investigations, data analysis, software design, implementation and testing, at times in collaboration with external partners or clinics. 

Working at RaySearch

RaySearch believes in investing in its people. We prioritize knowledge-sharing, creativity and collaboration, and you will work together with some of the most talented and highly educated people in the industry. We also have a strong social culture, with regular events and activities for employees. You will work in a modern office environment, with access to the latest hardware and tools. RaySearch is committed to equal opportunities. We value diversity and are dedicated to preventing discrimination. Read more about RaySearch.


You are welcome to send your application in Swedish or English. It should include a résumé, a personal letter and documentation of your university education (BSc and MSc). The recruitment process will be ongoing.

One positions are announced, but three topics are formulated. You reach the application form by the "Apply" button below.