What is Radiotherapy Physics?

Radiotherapy Physics encompasses a large variety of things, many of which may go unnoticed when a patient has their treatment. So, maybe it’s best to start with a smaller scope: What is Radiotherapy? Radiotherapy is the use of radiation to kill cancer cells or shrink the tumour.  This effect is achieved by delivering radiation which damages the cancer by causing breaks along the strands of the DNA. This is effective as cells have their own tools to repair the damage, however, in cancer cells these tend to be faulty. In fact, this is one of the reasons why treatments are spread out, to allow the healthy cells to recover somewhat before the next treatment. It is important that cells are allowed to recover between treatments otherwise the treatment may be counterproductive and harm the patient more than benefitting them.

A visual representation of DNA being broken down by radiation1.

There are a variety of techniques to treat cancer with radiation and within each technique, multiple methods of applying that technique. For example, we have External Beam Radiation Therapy (EBRT) which can be delivered through a method such as Volumetric Modulated Arc Therapy (VMAT) that is delivered using a LINAC (Linear Accelerator). This is where a LINAC fires a beam of ionising radiation, and the beam is shaped by something we call Multi-Leaf Collimators (MLC).

An image of MLCs creating a dynamic shape2.

Another example of a treatment method in Radiotherapy is Brachytherapy which may be delivered intracavitary (within a space or cavity). Brachytherapy is where a radioactive source is put within the body. This works as it allows the source to be right next to the tumour. In addition, the source usually has a relatively short half-life, i.e. Iodine (I-125) has a half-life of 60 days. So, to put it simply, after 60 days the source will emit half the amount of radiation it was originally, and this continues like this so after 120 days it will be a quarter of what it was originally and so on.

A few common questions I personally have been asked when I tell people I work in Radiotherapy are:

“So, you’re a Radiologist?”

“Oh? Like a Radiographer?”

These are both incredibly important roles within oncology specifically and medicine generally, however, a healthcare scientist in radiotherapy works alongside these professions with a different role. So why is it unlikely patients will be aware of a radiotherapy physics scientist? Well, a healthcare scientists’ main role in radiotherapy is regarding the precision and accuracy of the treatments. This may be via ensuring calibration of the various equipment used within the department such as CT (computed tomography) scanners and LINACs. 

An image of a LINAC where a patient receiving radiotherapy will most likely receive treatment3

In conjunction with ensuring the safety, precision, and accuracy of equipment, radiotherapy healthcare scientists may also be responsible for the planning of, and quality assurance of the plans created for treatment. It is paramount that the plans created are optimised, to make certain the patient is receiving the best possible care by maximising the control of the cancer and minimising the radiation delivered to the surrounding healthy tissue. 

Why Radiotherapy Physics?

A gloomy statistic to think about is that Cancer Research UK have stated that 1 in 2 people born after 1960 will have cancer in their lifetime, but on the other hand, cancer survival rates are improving and have doubled in the last 40 years, with 50% of people diagnosed surviving more than 10 years after their diagnosis. This is, in part, due to advancements in radiotherapy and being able to treat with increased precision and greater accuracy. The opportunity to be a part of the NHS, helping people’s lives and putting to use the problem-solving skills I had gained from my physics BSc really inspired me to go into this as a career. 

Image sources:

1 http://nuclearsafety.gc.ca/eng/resources/radiation/introduction-to-radiation/radiation-health-effects.cfm (accessed 10/01/23)

2 http://medphys365.blogspot.com/2012/04/multileaf-collimators.html (accessed 13/02/23)

3 https://www.oncologysystems.com/blog/making-varian-linear-accelerator-vault-obi-board-imaging-ready (accessed 16/02/23)

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