A Brief history of Radiotherapy
I am constantly fascinated by how things came to be. More often than not the best way to understand why something is the way it is, is to look at its history. So let’s have a brief look at the history of radiotherapy from the 1960s onward, only briefly that is. This will give you an outline as to how far we have come, and where radiotherapy is going.
I have already done a few post on the historical perspective of radiotherapy, but these were more focused on specific machines. Starting off with the earliest machines in an era I call the prehistoric era of radiotherapy. Then there was the early years of kilovoltage machines, the era of cobalt-60 machines, and then the modern Linac. This is a more broad overview.
First of, I am going to be honest. In the 1960s Radiotherapy had a low probability of success. In this era radiotherapy was an empirical discipline, that is it was mostly based on clinical experience rather than any scientific evidence. Don’t Worry, this has changed greatly over the last 50 years.
Radiation therapy has been largely based on physics, mathematics, computer science and radiation biology. There is also a healthy input of electrical and mechanical engineering, combined with human anatomy and pathology. This makes radiotherapy a truly interdisciplinary field, unparalleled with any other clinical discipline. Arguably, one of the most multidisciplinary department or workplace around.
The combination of all these disciplines have created a therapy that can be applied safely, precisely, and efficiently. Improvements over the years have eliminated many of the feared side effects of radiation therapy completely. While at the same time increasing the probability of a cure! Most of these improvements have stemmed from the world of physics, and carved out the physics discipline of medical physics.
This change from an experience to a scientifically based profession has only been achievable through advancements in physics and technology. One of the first big steps was getting rid of the older generation machines, like the cobalt-60 machine, betatrons and other older style accelerators. This was done in favor of the far superior linear accelerator.
The linear accelerator was introduced between the 1960s to the 1980s, now they are the workhorse of radiotherapy and commonly known as a LINAC. These machines are compact, reliable, safe, and accurate compared to the older style machines.
The next great invention, again stemming from the world of medical physics, was the x-ray computer tomography machine, sometimes called a CT, or CAT scan (computer automated tomography). CT scanners started to become widely available in the 1970s. This allowed the doctors the ability to visualize the targeted tumour in a three dimensional way.
No only did the CT give the radiation oncologists a better understanding of where to deliver the does, it also gave physicists data to be able to calculated the dose delivered from combination of radiation beams. Prior to this, the amount of dose delivered was estimated using charts and table. Now models of the linear accelerators were being created to calculate the dose delivered to the patient right on the CT scan of the patient.
At the same time as the introduction on CT imaging the development of linacs continued and became the workhorse of radiotherapy. They became efficient compact machine with multiple modes and radiation types, a truly versatile machine. CT imaging was soon superseded by MRI for the image quality in soft tissues. Combining this with CT imaging allowed for improved planning of dose delivery and tumor outlining.
“The computer revolution, characterized by the development of small, powerful and inexpensive desktop computers”
While all these technologies were being developed, the computer revolution was fully under way. Computers radicalized radiotherapy! In an era of 3D computer graphics a method of planning treatments in a virtual 3D world was created. New algorithms were created to calculated where the dose was being delivered with great accuracy. This is a huge improvement over just estimating how much and where the dose is being delivered. Before this, treatments would consist of just treating large areas of the body to insure that the entire tumor would get radiation, risking a lot of normal healthy tissue.
After the ability to calculate dose in a virtual world was created radiotherapy could be individualized for each patient using a CT scan of the patient themselves. Where the system was lacking was transferring the treatment plan from a CT scan to the patient with high accuracy. This is because the patient was never in the same location as when they had their CT scan performed.
This was solved using a technique called stereotaxy which was taken from neurosurgery in the 1980s. In neurosurgery stereotaxy is where the head is held in a very rigid way so that neurosurgeons can precisely pinpoint location inside the tumor. In Radiotherapy it involves fixing or immobilizing the patient. This improves the accuracy of the delivery. It basically tries to make sure the patient is in the same position as when they had their original CT scan.
This method in radiotherapy gained the name stereotactic, or radiosurgery. It started of being only one treatment of high dose radiation, but later there treatments were given over 5 or so sessions. Many of the methods used in stereotactic were introduced to all radiotherapy techniques. Making head molds is common for all head and neck patients now, body molds are common for pelvic and abdominal treatments.
In the middle of the 1980’s the linacs could only treat square-shaped fields. This is not great as people aren’t very square. The development of the multi leaf collimators gave linacs the ability to make irregular, or non-square shapes. A multileaf collimator is basically a large number of different sliding leafs that can be moved in and out independently. Allowing the radiation beam to be shaped to the tumor, lowering the dose delivered to healthy tissue.
Making beams conform to the target became far cheaper than ever before. And the combination of being able to plan in a virtual space and conform the beams better meant radiotherapy became safer and more efficient. By the 1990s radiotherapy had moved on from several stationary shaped fields to several intensity modulated fields. This techniques is known as intensity modulated radiotherapy, or IMRT. This is where each beam is made from several different shaped fields, allowing to change the amount of dose delivered across the beam.
Because of the complexity of trying to manually plan this was too much, a new class of algorithms was created. This algorithm is called inverse planning. It start of by calculating the ideal dose that is required, and then calculates how and from which direction the IMRT fields will be delivered from. This is now the standard tool in most radiotherapy centers.
This is where the improvements in conforming the dose to the target has basically reached a limit. From a physics point of view the dose cannot be made anymore conformal because of the way photons interact as they pass through tissue. There is always an amount of tissue that will receive some radiation. It is unavoidable.
To move beyond this would require the move into particle therapy. The characteristics of protons, and heavy atoms is completely different from photons. The dose delivered by these particles is basically all delivered just before the particle stops inside the patient. While for photons it is a continuously decreasing amount of dose from entry to exit. And by changing the energy of the particles you can change the depth inside a patient where it will stop, effectively selecting where you want the dose to be delivered. This produces a much lower dose bath to the healthy tissue around the tumor, and the ability to give much higher doses to the tumor.
The advantages of proton and heavy particle therapy has been known for a long time. But the technology is complex and is still in its early stages of being widely adopted. Currently there are a large-scale trials going on to try to scientifically prove and demonstrate the benefits of these technologies. One of the largest hurdles it is facing however, it is enormous cost.
One of the cheaper ways to improve radiotherapy, and in fact is a standard now it to use Image guided radiotherapy. Once CT scans were invented they were at the beginning of the planning stage and that’s about it. Who knows during treatment where the tumor is, if it has grown or shrunk. In the mid 2000s, CTs were integrated with Linacs giving radiotherapy the ability to image a patient minutes before the treatment is to be delivered. This gives them the ability to check the precise patient location in terms of internal organs, not external patient contours.
This is quickly being developed into real-time imaging, where the patient can be monitored during treatment and if any movement is detected the radiation will pause until the target is back in the correct position.
Another way of improving radiotherapy is to start implementing biological adaptive radiotherapy. Traditionally it was thought that tumor cells inside a tumor where all the same, and would all react to radiation the same. It has now been shown that this is not the case. Some areas of tumors seem to be able to survive higher doses than other areas. If it is known where these cells are within a tumor more dose can be delivered to this area. Methods to determine this are currently being developed using MRI and PET scanners.
The speed of development in radiotherapy is at such a pace that all the professionals inside radiotherapy need to constantly be retrained to be able to used the new techniques and methods. This also allows old methods with little or no scientific evidence to be quickly removed from standards of practice. Remembering that the era of scientific based medicine only really started in the 1980s, before this most medical procedures did not have rigorous scientific evidence for their effectiveness. Rather many procedure were based on anecdotal evidence. I’m not talking just radiotherapy, the whole of medicine operated on this principle.
Radiotherapy has always been fast to adapt to new technologies and techniques, and this does not look to change in the near future!
That is all for now, I hope it is not too much information to take in. If something doesn’t make sense to you I am happy to try to explain it better for you. Please just reply in the comments, or contact us.
One more thing, we have heaps of ideas for posts here at Radical Radiation Remedy, but please contact us if you would like use to do a post on a certain topic.
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Originally published at www.radicalradiationremedy.com on February 9, 2017.
