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Physics Master Thesis: Monte Carlo simulations of 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 set up and use a Monte Carlo simulation framework, such as Geant4, to extract and understand physical distributions needed for carbon radiation therapy.  The second step is to evaluate the current model sensitivity to input, and relate this to the physics approximations present in different state-of-the-art Monte Carlo codes. 

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 (for example the Local Effect Model, LEM) take into account e.g. the track structure of ionization generated around the primary carbon ion and the secondary nuclear fragments generated in the patient material.

The optimal plan for each patient is determined using a treatment planning system (TPS), such as RayStation® by RaySearch Laboratories, where an analytic dose calculation with LEM is implemented. This calculation relies heavily on physics input from external sources, which can be either measurements or Monte Carlo particle transport simulations with multi-purpose codes such as FLUKA or Geant4.

To develop the analytic dose calculation in RayStation further, and take steps towards the development of a new Monte Carlo code for carbon ion treatments, there is a need to perform extensive in-house physics simulations. 

The specific objectives are:

  • To set up a new environment to simulate ion therapy geometries using one or more Monte Carlo codes.
  • To apply Monte Carlo simulations to extract distributions of the physical quantities needed for carbon ion dose calculation and relative biological effect.
  • To compare the results of different codes to each other and understand their differences in terms of implemented physics models.
  • To analyze how different physics implementation lead to differences in dose and relative biological effect.
  • Time permitting, to implement selected results 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.

Previous experience of using and setting up a Monte Carlo simulation framework, such as Geant4, would be helpful in this task, but it is not a requirement. 

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.