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Physics Master Thesis: Tumor tracking for ions

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

The topic is to implement support for tracking of moving tumors in ion radiotherapy.  While providing excellent dose distributions for stationary targets, ion radiotherapy plans suffer from large distortions when the target is moving. The most advanced solution to this problem is to follow the tumor with the beam while adjusting different physical parameters. The end goal is to provide better chances for survival and less side effects for cancer patients receiving radiation therapy at centers using scanning ion techniques.    

Your tools for this task are RaySearch’s powerful treatment planning software RayStation, the RayStation scripting interface in Python and the RayStation development code in C++ and C#. As support you will have your supervisors at RaySearch, the RaySearch crew in general and the physicists particularly.

Background and purpose

Ion therapy (e.g. proton and carbon) is rapidly becoming available for a larger population of cancer patients. In modern ion treatments, the dose of ionizing radiation is delivered to the tumor using a large number of very thin pencil beams to paint the target volume. The amount of radiation going into each pencil beam is described in the patient-specific treatment plan, which is determined by mathematical optimization of the dose distribution taking the patient geometry and physical characteristics of each pencil beam into account. This provides means to precisely shape the dose distribution to the wanted treatment volume.

Currently, the time-dependence of the delivery of the treatment plan is not considered during optimization. When breathing motion and other changes in the patient geometry occur on the same time scale as the treatment delivery, there is therefore a high risk for insufficient quality of the delivered plan, and hence a reduced chance of survival for the patient. This problem can be addressed by tracking the tumor with the beam, so that the pencil beams deliver the desired dose to the tumor throughout the delivery. Tracking is achieved by changing the physical parameters, e.g. position and energy, of each pencil beam in real-time during delivery.

The aim of the project is to find strategies for optimization and generation of tumor tracking plans.

The specific objectives are:

  • To implement support for tumor tracking for ion radiotherapy in a research version of RaySearch’s commercial treatment planning system RayStation®.
  • To develop tools to evaluate the resulting dose taking the changing patient geometry and the delivery time-dependence into account.
  • To evaluate the implemented method with respect to plan quality, optimization time, delivery time and robustness, and compare it to other methods used for delivery to moving targets.
  • To investigate possible implementation strategies of tumor tracking at the clinic.

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 (preferably in Swedish but English is also fine) by clicking on the button below. It should include a résumé, a personal letter and documentation of your university education (BSc and MSc). Mark the application “Physics Master Thesis 2018”. 

Three positions are announced, but six topics are formulated. The recruitment process for the three positions will go through the same contact point. Please send in one application and indicate clearly all projects of interest (including your thoughts on what would suit you and interest you the most).   

The recruitment process will be ongoing while this posting is present. To enquire about the status of your application, please email ansokan@raysearchlabs.com.