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Physics Master Thesis: Spot patterns for scanning ion radiation therapy

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 find and evaluate a number of methods to create dosimetrically optimal pencil beam scanning plans while taking the minimum number of protons per spot into account. 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 physicist 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 (or spots) to paint the target volume. The amount of radiation going into each pencil beam is described in the patient-specific treatment plan.

It is the task of the treatment planning to obtain an optimal plan for the patient from a set of specified mathematical objectives. This is performed by solving a large optimization problem, while taking into account non-linear elements due to delivery machine limitations. For example, there can be a minimum number of protons that can be delivered in one spot.

Since different treatment machines have different constraints, it is important that these are handled with enough flexibility without compromising plan quality. In addition to improving the plan, it is desirable for clinics to minimize the total treatment time and to have a fast plan optimization since this has a proven effect on plan quality.

The aim of this project is to investigate and develop an optimal strategy to handle all these aspects.

The specific objectives are:

  • To develop and evaluate different strategies for non-regular placement of initial spots for pencil beam scanning, considering e.g. target and aperture geometry.
  • To develop improved methods to take into account machine constraints in the spot weight optimization, in particular with respect to the minimum spot weight.
  • To investigate methods to make use of non-uniform spot sizes within one scanning pattern and evaluate their benefit.
  • To evaluate the proposed methods with respect to plan quality, optimization time, delivery time and robustness.
  • Time permitting, to implement an optimized strategy 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 (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.