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David Bolst is a PhD student working within the field of 鈥淢edical Physics鈥�. He is investigating how best to use silicon microdosimeters in hadron therapy using Monte Carlo simulations. His supervisor Associate Professor Susanna Guatelli is an international leading expert of Monte Carlo radiation transport simulation codes for radiation physics, including medical applications and radiation protection in Earth labs, aviation and space.

Meet the supervisor: Associate Professor Susanna Guatelli

Can you explain your area of expertise?

My area of expertise is the development and use of Monte Carlo simulations to solve medical physics problems such as how to improve a specific radiotherapy treatment or how to improve technology associated with radiotherapy and imaging. Monte Carlo simulations are an extremely powerful tool because they allow to solve theoretically problems which may be difficult or expensive to solve using experimental techniques only.

At the Centre For Medical Radiation Physics, we use Monte Carlo simulations to design and characterise novel detectors for Quality Assurance in radiotherapy and imaging, and for radiation protection of astronauts and aviators. In addition I contribute to improve the Monte Carlo simulation code Geant4 (www.geant4.org), maybe the most used Monte Carlo code of its kind in the world for radiation physics, for medical applications. Geant4 is developed by a large scientific international collaboration based at CERN and I am part of this international effort since 2003, when I was a Master student in Italy.

How did you find yourself where you are now professionally?

I never had a strategic career plan. I studied physics because I wanted to learn about nature, from atoms to the cosmos, independently from anything else, e.g. a specific job or career. I did the PhD and then research because of my curiosity and my greed to have new challenges. What helped me in my career so far is that I never lost an occasion to learn and I always tried to improve and do my best. I have always been ready to travel and move to other countries in order to fulfil my aspiration to perform research. I think my flexibility and to be open minded helped me a lot in my academic career. In summary, I just did what I liked and then one opportunity led to another one and so on.

What makes a great PhD candidate?

A great PhD candidate is extremely curious, keen to learn, extremely dedicated to his/her research. He/she should be keen to work hard and spend many hours per day, nights and weekends on the research. Motivation is 50% of a successful PhD. A great PhD will be the one that at the end of the program is an international expert of his/her research field and will be able to lead research in that specific topic.

How do you guide candidates on their journey?

I have weekly group meetings where all students report on their progress and possible problems and challenges. We discuss all together and propose possible solutions to solve specific problems. Such meetings are also a good opportunity for the students to network and learn from each other. Then, when required- I have one to one meetings with specific students. I try to be very clear on my expectations and I am very honest with my PhD students when I provide feedback on their achievements and progress. To have a regular and clear communication with the PhD student is crucial for the success of a PhD project.

What should candidates consider when finding a supervisor?

First of all, they should find a project they are really passionate about. So I encourage candidates to approach and talk with few potential supervisors to reach a more informed decision. Second, my suggestion is to talk with previous students of a potential supervisor to have information of the working/research environment. Most importantly, candidates should find a supervisor they trust and with whom they have good communication.

Meet the candidate: David Bolst

Can you give a description of the topic or question you are investigating?

The main focus of this project was to look at how best to use silicon microdosimeters in hadron therapy using Monte Carlo simulations.

Microdosimeters are devices which mimic the sizes of cell nuclei and allow radiation to be characterised in terms of how damaging they are biologically, this is particularly important in hadron therapy since the beam鈥檚 biological effect varies significantly in different positions in a patient. While Monte Carlo simulations are a method of generating 鈥減seudo-random鈥� numbers to model probabilistic problems such as radiation in matter or even throwing dice, hence being named after the famous gambling region of Monaco.

How did you select your research topic? Where does your interest in this field stem from?

I would describe my main current field as transport of radiation using Monte Carlo, which I entered via the field of 鈥淢edical Physics鈥�, which is what my bachelor鈥檚 degree was on. I originally entered medical physics from feeling obligated because I got a phone call from one of the medical physics academics one day and said something on the lines of: 鈥淥h I see you put us down on your list. If you put us first we鈥檒l accept you in the rounds.鈥� Now they weren鈥檛 offering me any money but I figured if they took the time to ring me then I should probably accept their offer.

To answer how I entered the world of Monte Carlo for radiation transport, which involves quite a lot of programming. In my first year of my degree I was advised to take programming as an elective but I was scared of programming so I avoided it like the plague. In third year, as part of the degree, you have to do a Monte Carlo lab and I absolutely hated it. But in the last session of the bachelor degree I finally took that programing subject originally recommended and life made much more sense when starting from the start. So I quite enjoyed the elective and that鈥檚 the reason I chose to do an honours research topic in Monte Carlo with Susanna, who continued to be my PhD supervisor and currently my postdoc supervisor.

So you could say that my interest in my current field (Monte Carlo for radiation transport) came from doing an elective in a bit of a different area. And after six plus years of doing Monte Carlo simulations, I still love that feeling when I get insights into a problem. For instance you might observe a result in an experiment which seems a bit strange and you aren鈥檛 sure if this is real or not, many times a Monte Carlo simulation can help explain the cause of this.

How did you find your supervisor?

Susanna taught me a couple of subjects during my undergrad and when honour鈥檚 projects were being advertised, she had a study on proton therapy with Monte Carlo. I signed up and haven鈥檛 had any regrets going down the Monte Carlo route under Susanna鈥檚 supervision, with the support of Dist Prof Anatoly Rozenfeld as co-supervisor

How do you think your research can change the world?

For the main project, hopefully it will increase the accuracy of quality assurance in hadron therapy when using silicon microdosimeters. In terms of the number of people, I think the largest impact might actually be from an offshoot from the main project goal. This was evaluating the performance of certain physics models in the Monte Carlo code Geant4, one of the most common Monte Carlo codes used in medical physics. This test allows anyone to view how different models perform for a particular version of Geant4 and is particularly important if you are interested in studying the dose being delivered to healthy tissue for patients

What advice would you give someone considering doing postgraduate studies?

To quote everyone鈥檚 favourite nuclear power plant owner. 鈥淭he only 鈥渟hip鈥� that gives a dam is friendship.鈥� To elaborate a bit, during your PhD you鈥檒l face many problems, some might become quite frustrating and put you in a bit of a rut. It鈥檚 good to be able to have a break and do something else to forget about the problem for a while and clear the head. On a similar note, it is good being about to commiserate and talk things out to others.

If you鈥檙e looking at doing a PhD in a group you haven鈥檛 worked with before maybe look through the latest publications of the group/prospective supervisor to get an idea of the type of research the group is currently active in. You may not want to spend three plus years on a project that doesn鈥檛 interest you so do some homework before.

• ASSOCIATE PROFESSOR SUSANNA GUATELLI: To find out more about Susanna visit her 
• DAVID BOLST: To find out more about David, take a look at his