Clinical proton therapy at the Paul Scherrer Institute, Switzerland

I am a trainee on the Scientist Training Programme (STP) in medical physics, specialising in radiotherapy physics at The Christie Hospital NHS Foundation Trust in Manchester. I chose the Christie because it is renowned for advancing cutting edge techniques in radiotherapy and I thought it would be a great place to learn from people with expertise in lots of different areas. An exciting development is that the Christie, along with University College London Hospitals, has been chosen to deliver a Proton Therapy service to the UK. Proton therapy is a form of radiotherapy where protons are used to irradiate and kill tumours rather than high energy X-rays. The advantage is that healthy tissues can be spared to a much greater extent, causing fewer side effects. For many patients, particularly children or those with tumours close to parts of the body that are very sensitive to radiation (such as the spinal cord) this treatment could offer significant benefits.

I decided to visit a clinical proton therapy centre for my elective because I wanted to learn more about how such a service is implemented from the physicists’ perspective. The Paul Scherrer Institute (PSI) in Switzerland has developed an innovative technique of proton treatment delivery, called ‘spot scanning’, that we will be using here at The Christie so I speculatively applied to go there for six weeks. Unsurprisingly, the department of medical physics at PSI had been inundated with trainee medical physicists from the UK hoping to spend their elective placements there! Luckily, they were able to fit me in with three other STP trainees in January and February 2014. All of us self-funded our electives.

The first week was spent at the PSI Winter School on Proton Therapy, an educational meeting for proton physicists and oncologists from across the world. The lectures were really useful and gave us a solid background for the rest of the placement. We also got to go to the Flumserberg Ski Resort on the social day which was breathtakingly beautiful.

The rest of our time at PSI was split between clinical experience and project work. I was assigned a project which involved working on some software that takes the information provided by a CT scan (Hounsfield Units) and converts it into information that can be used to calculate how the dose from a proton beam is deposited inside the patients’ body (proton stopping powers). It was also interesting to see presentations of the research going on at PSI.

We spent time with medical physicists learning how the dose output and accuracy of proton therapy beam delivery systems was thoroughly checked before use every morning and how the safety interlock systems worked. We followed patients through the whole process of their treatments; from having their radiation treatments planned on their CT scans by physics in collaboration with their oncologist and having their immobilisation devices made so that they could be exactly positioned in the same way for each fraction of their treatment, through to the treatments themselves.

Since protons are charged particles, they behave very differently inside the body than photons. That meant that there was a lot to learn in terms of how doses are predicted and checked and how treatment plans are optimised!

These were experiences I could not have had in the UK at the current time. I learnt a lot about different aspects of proton therapy and thoroughly enjoyed myself in the process. I would encourage anyone thinking about their elective to focus on an aspect of their specialism that particularly interests them and to approach people who work in centres that are related to that topic. After all, the elective is a rare opportunity to gain experience outside of the norm, and if travelling abroad is involved, all the better.

Jenny Richardson, Radiotherapy Physics trainee, The Christie Hospital NHS Foundation Trust