How are Physics and Radiotherapy Related?


So what does physics have to do with radiotherapy, and for that matter what does physics have to do with medicine? Isn’t physics done at high tech laboratories such as the large hadron collider, or at governmental institutions such as NASA. What could physics possibly do in healthcare and what exactly is a Medical physicist?


It might surprise you how much physics has done for radiation therapy and healthcare in general for that matter. So let’s look at how what physics has done for radiation therapy.


Physics and Radiotherapy


There is a lot of physics going on throughout the radiotherapy process. Many of the devices made were originally invented by physicists and the underlying principles of radiation is a purely grounded physics.


The progress radiation therapy has been making over the last century is mostly because now we can better aim and deliver radiation to tumors. These improvement have come from physics discoveries and improvements in technology.  


As far as radiotherapy has come, there is plenty scope for left for further improvements, for example the improvements in image guided radiotherapy and four dimensional motion management that will come with fast MRI imaging.


There is also more room for improvements in efficiency and cost effectiveness, as most of the treatment machines are in the range of millions upwards.


Beyond the improvements of technology, the biggest challenge for medical physicists is the move from just measuring radiation doses to biological dose. Medical Physicists are pretty good at measuring radiation doses but biological doses are another story.


So How Has Physics Improved Radiotherapy


As mentioned, physics has continuously improved radiotherapy by continuously introducing new discoveries and inventions from physic research into the clinic. There have been many examples of this over the  year. From advanced computer algorithms to calculating dose, to machines for imaging such as MRI and CT machines.

The most reason of which are the MRI Linac- which has just been released commercially to the public, and proton therapy machines.


Even though research physicists get a lot to the credit, there are far more clinical physicists looking after these machines and ensuring they are performing correctly. These physicists constantly perform checks and measure doses to ensure everything is perfect for patient treatments.


What Has Physics Achieved so Far


So let’s have a look at what physics has achieved in radiotherapy so far.


Obviously, it all started with the discovery of x-rays by Röntgenin 1985. It’s hard to argue that this wasn’t the greatest contribution by physics to medicine. This discovery lead to several new fields in Medicine; Radiation Therapy, Radiology, and Nuclear Medicine.


The field of radiology and radiation therapy started only 1 year after the discovery of radiation in 1985. The benefit and usefulness of radiation was recognized early on.


From this time on medical physics has been obsessed with finding better ways to deliver this radiation. Forever improving the precision and accuracy of delivering radiation dose to tumors. And so far this has been achieved through new treatment machines and patient imaging techniques, and computer algorithms for predicting dose delivery.


Not all physics discoveries have been implemented in medicine as quickly as x-rays. Discoveries like proton therapy and positron emission technology took decades before they were implemented into medicine. Protons were used in a new treatment technique of proton therapy, and positrons were used inside PET imaging.


Alongside these discoveries, improvement of delivery came through the constant improvement of linear accelerators. These are now the workhorse of radiation therapy.


Over the years these machines have been improved through increasing the energy of the radiation delivered to improve the skin sparing effect, to minimizing the size of the radiation source, and the ability to make complex beam shaped through the addition of multileaf collimators.


The geometry of the machines has also improved, Linacs can now rotate a around a patient with sub millimeter accuracy- quite impressive for a machine that weighs several tonnes. Imaging on board these machines, along with robotic couches can now also position the patient to within sub millimeter accuracy. This helps with dealing with organ motion, ensuring critical organs at risk are not receiving too much radiation dose.

It’s All in the Software


Improving the Linac and patient position to sub-millimeter accuracies is all great, but if you can’t predict the radiation delivery to this level of accuracy it is useless.


Improvements in software had to be made alongside the improvements in delivery techniques. These improvements started when computers were developed in the 1960s and 1970s.


A change occurred, form manual planning using graphs and tables (way before my time) to using computers to calculated dose distributions. This helped create a technique called 3D conformal radiotherapy. Where radiation beams were now conformed into shapes that mimicked the tumor, rather than squares and rectangles that were aimed at the tumor.


From then on, the software has improved so quickly that it is always waiting on the hardware to keep up. It is common for planning computers today to run at least 32 processors with 128GB of ram. Each clinic having tens for these computers to plan patients treatments.


Planning systems today have moved to inverse treatment planning- were you tell the system you want this much dose here and it works out a way of delivering it. Whereas before you manually position the beams and then calculated the dose delivered.


Images are the key


OK, so the improvement of Linacs is needed, as is the improvement of treatment planning software, but they all rely on the improvement of patient imaging techniques. Otherwise these improvements have no data to work with.


CT was developed by physicists in the 1960s and 1970s. This is probably the second greatest contribution by physics to medicine after the discovery of x-rays. There was even a Nobel prize given to Sir Godgrey Hounsfield and Dr Allan Cormack- a physicist, for developing it.


CTs are now used to create data sets on which doctors can use treatment planning algorithms to calculated dose distributions and the Linacs can calculated patient positioning corrections using the robotic couch tops.


Physics and Radiotherapy


So you now not the Physics and Radiotherapy are intrinsically linked to each other. Radiotherapy wouldn’t be where it is today without physics. Physics has help improve all aspects of radiotherapy, from the treatment machines to the software. Thanks to clinical medical physicists and research physicists radiotherapy is helping millions of people deal with their disease every day!