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Physics Master Thesis: Biological effect of carbon radiation therapy (LEM IV)

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 and evaluate an updated model for the relative biological effect (RBE) of carbon irradiation, the so-called Local Effect Model version IV. 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 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.

Several models are used to describe this effect, taking into account e.g. the track structure of ionization generated around the carbon ion as it traverses the cell nuclei.

At European centers, clinical treatments are planned with an RBE calculated using the Local Effect Model (LEM). The optimal plan for each patient is determined using a treatment planning system (TPS) where this model is implemented. RaySearch develops and sells the RayStation® TPS, which currently supports carbon ion RBE calculation with the first generation of LEM (LEM I).

The Local Effect Model exist in newer, more advanced, versions. The most recent of these is LEM IV. This project aims to perform a complete study of the similarities and differences between the presently implemented model and LEM IV, covering all aspects of treatment planning.

The specific objectives are:

  • To implement the Local Effect Model version IV according to specifications in the literature.
  • To verify the new implementation against existing references.
  • To generate input data for different cell types using the LEM IV implementation.
  • To investigate the ability to use LEM IV for carbon ion planning, optimization, and dose calculation in RayStation®.
  • To perform comparative planning studies with LEM I and LEM IV.

Time permitting, to implement LEM IV 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.