For GPs

Better than sci-fi: unravelling the sophisticated mysteries behind modern radiation therapy

09 Aug 2017

The last blog post, as great as those prostrate animal pictures were, ultimately did a great disservice in failing to mention the behind the scenes heros of radiation therapy – the medical physicists. The brainiac, ever-reliable, quiet achievers of the radiation therapy team – they are the ones who make fantasy into reality, ensuring that the whiz bang radiation plans we develop for our patients can actually be delivered in the real world. While the radiation oncologists and therapists may be the ones being seen to save lives, the medical physicists save our lives in checking a treatment plan is safe and usable.

As such, I thought it would be good to interview Chief Medical Physicist, Sean Geoghegan about the ins and outs of the medical physicists’ work, and what sci-fi-esque things are possible now with modern radiation therapy (radiotherapy).


Q: Hi Sean. What’s a usual day like for a typical medical physicist working in a cancer therapy centre?

Sean: The first thing to say is that each day is so varied with so many different things – an aspect of our work that I love. Generally, we start bright and early, before most of the rest of the cancer centre arrives to run up the treatment machines and ensure they’re working as they should before patients arrive. I guess it’s akin to doing all the checks on an airplane before take-off which I’m sure any passenger would appreciate and expect!

Once up and running we may spend the working day on research and development projects, perhaps working towards implementing a new treatment technique. About one day a week we’ll be working on a machine as part of a scheduled maintenance program and make sure it is calibrated. This is all part of a comprehensive quality assurance program we run. We may do some calculations for a treatment plan for a specific patient, review treatment plans and if new equipment is being installed then we’ll be working on commissioning it by rigorously testing it.

Once the treatment day is over we get back onto the treatment machines to test and validate patient specific plans and any new technique that we’re working on. This is when the coffee and chocolate from earlier in the day become so handy!


Q: You guys really are like the bookends to the whole radiation therapy process, starting the day off for us and warming things down at the end. Now I’ve only been working in radiation therapy personally for 4 years, but even I know that there have been incredible technological advancements breaking through every year in radiation therapy and it’s not what it used to be – almost like comparing an old-school discman (they were the hippest at the time) to the latest ipod.


What would you say to people who still think of radiation therapy as the same as from a decade or more ago?

Sean: I agree. I have seen massive progress in radiation therapy over the past decade. I am astounded by how accurately and precisely we can now deliver radiation to a patient. Radiation therapy is not what it used to be in the 70’s or 80’s, or even in the 90’s and the beginning on this century. I think most people would be surprised to learn about the amazing things that are now possible with modern radiation therapy to better benefit our patients. My job is like making the technology shown in Star Trek happen.

With a well calibrated and maintained system, we can aim a radiation beam to within 0.6 mm of where we want it to go. This is amazing considering we have about 4.5 tons of steel and electronics that makes up a treatment machine rotating around a patient. We can deliver a radiation beam from almost any direction and shape the radiation field to cover the disease and spare normal tissue. For example, we can accurately destroy a small cancer in someone’s brain using radiosurgery.

Q: Wow, yes, because one question I get asked a lot by patients is about the accuracy of radiation therapy, and also about how we can spare the healthy non-cancer tissue?

Sean: A large portion of getting this level of accuracy and precision is from having good medical imaging systems. We couldn’t achieve all this without having high resolution CT and MRI scans. Medial physicists also ensure the imaging equipment is accurate – add that to the list of what we do!

There are also treatment techniques that spare normal tissue such as Intensity Modulated Radiation Therapy (IMRT) and Volume Modulated Arc Therapy (VMAT), which allow something called “dose painting”. Previously a disease that wrapped around a critical structure (a normal tissue we want to avoid with radiation) would mean that the critical structure would also get a significant dose, however now we can design the treatment fields to essentially miss critical structures whilst hitting the target. The mathematics and physics underlying this is beautiful, and we see a direct impact on patients receiving treatment by being able to treat disease with minimal side effects.


Q: And all that delivered within minutes, with no pain, no scalpel, no recovery time in a recovery bay! Okay, but what about the fact that sometimes our target is a moving target, with normal respiration and physiological movements?

Sean: Another technique that is developing and being used in more and more radiation treatment centres is trying to counteract small body movements over time. As you say, obviously our breathing affects the position of our organs, particularly those in the chest but also in our abdomen and pelvis. We’re now moving into four-dimensional radiation therapy where we use imaging to see into the patient’s body and how things move over time. We can either make the treatment machine “breathe” in time with the patient or ask the patient to control their breathing when the machine fires a beam, the patient holds their breath at a certain point in their breathing cycle. Implementing and testing these new technologies are what makes our lives as medical physicists so rewarding. We really can see the equipment being made more human sensitive.


Q: Thank you Sean. What a great insight into the technical aspects of our specialty.

Radiation therapy really is an interface where clinical practice meets technical processes. Together there is sophistication of treatment delivery which ultimately enhances and progresses cancer care for those who need it most. The result is more cure, and reduction of patient side effects – helping our patients, as they say in Star Trek to:




About the Author: Dr Eun-Ji Hwang is a Radiation Oncologist Registrar in Sydney, trying to stop the confusion around radiation therapy.

Find out more about the role of a Medical Physicist

Read Dr Hwang’s first blog “What Radiation Therapy is NOT