There are many explanation of what radiotherapy is on the internet. Many can be found on websites from credible organisations. They are almost always correct, but generally they all have one downfall. They are very short and all assume you have some knowledge on subjects like radiation physics and radiation biology. Take a look at the following definitions of radiation therapy.

“Radiation therapy is one of the most common treatments for cancer. It uses high-energy particles or waves, such as x-rays, gamma rays, electron beams, or protons, to destroy or damage cancer cells. Other names for radiation therapy are radiotherapy, irradiation, or x-ray therapy”


…Or this explanation from Wikipedia


“Radiation therapy or radiotherapy, often abbreviated RT, RTx, or XRT, is therapy using ionizing radiation, generally as part of cancer treatment to control or kill malignant cells and normally delivered by a linear accelerator.”


… Clear as Mud isn’t it?…


They are good definitions by all means. I am just not that sure that everyone knows what high-energy particles are, or what ionizing radiation is?… and what is a malignant cell? Normally delivered by a linear accelerator what is that? Electrons, x-rays, gamma ray, what are all these?


So it is true that Radiotherapy is an essential component of modern cancer care. More than half of all patients diagnosed with cancer receive radiotherapy.  Just for interest sake the two other common cancer treatment are chemotherapy and surgery.  


If you want a basic explanation of how all three cancer treatment work just imaging how you would weed a garden. You can pull out or cut the weed. You could use chemicals to poison the weeds. Or, you can get serious and burn the weeds. So you options are to either slash, poison, or burn. In a simplified way you can say that this is equivalent to what the goal of surgery, chemotherapy, and radiotherapy is in terms of cancer treatment.


….Slash, Poison, and Burn…..


Surgery aims to cut the tumor out, physically removing it. Chemotherapy aims to poisoning the tumor,  and over time the tumor shrinks and disappears. And Radiotherapy is somewhat similar to burning the tumor. Delivering energy to the tumor to physically destroy the tumor.  It all sounds a bit barbaric doesn’t it? Trust me though, it isn’t that simple.


Malignant cells


OK, so how does radiotherapy kill the tumor?


Firstly, a tumor is just consisted of a type of cancer cells, these are called malignant cells. Cancer cells are just abnormal cells. Cells that don’t serve any function inside the body. There can be abnormal benign cells, and malignant cells. Benign cells do not reproduce in an uncontrollable way and so they don’t generally cause tumors to form. They can often be removed, and, in most cases, they do not come back. Malignant cells do reproduce uncontrollably and form tumors. If left alone these uncontrollable cells can spread around the body using the blood or lymphatic system to form secondary tumors called metastases.


These abnormal cells can occur when the normal reproduction of healthy cells goes wrong. Generally when this has happened the cells will just die, end of story. But occasionally the cell doesn’t die, and since it has been reproduced wrong, it can’t perform its original task. This is an abnormal cell.  If this cells starts reproducing itself it becomes cancerous. Multiplying so often that it forms a tumor.


So for a tumor to form you need a cell to incorrectly reproduce, then the incorrectly reproduced needs to stay alive, after which it needs to reproduce multiple times itself.


So now you know a bit about how malignant cells are formed and create tumors, now how does radiotherapy “burn” the tumor. The answer is radiation.


Not just any type of Radiation


Ionizing radiation, x-rays, gamma rays, photons, and electrons. What are all these? These are all types of radiation. More specifically a category of radiation known as ionizing radiation. Ionizing radiation has a lot of energy. Enough energy to do serious damage to the cells that it encounters. The Damage is done by ionizing molecules and atoms inside cells. Ionizing is where the radiation rips of electrons, causing the molecules and atoms to form ions- which are molecules or atoms that have a charge. That is why it is called ionizing radiation– radiation that causes ions when it interacts.


There are other types of radiation that cannot ionize stuff- called matter if you like to use the physics term. This radiation includes radio waves, infrared radiation, visible lights, and many others including your mobile and WiFi signals. These don’t ionize matter- and hence have little effect on cells.


So the only difference between all these types of radiation is the energy they have. Ionizing radiation has a lot of energy and non-ionizing radiation has less energy. I tried to think of a metaphor for this difference in energy. I couldn’t think of a great one, but maybe you could share one with me in the comments. The one I could come up with is one about bullets.


The difference between a lethal bullet and a non lethal bullet is its speed. You can basically relate the speed with the amount of energy the bullet has. If it is fired from a gun it has a lot of speed- a lot of energy. It is then lethal and dangerous to anyone who comes in its way. When you simply dropped the bullet on someone it is slow, it doesn’t have much energy. The bullet is not lethal in this situation. It will just cause a bruise if it falls on someone. And if it doesn’t move at all it has nearly no energy it will do does nothing.


  • Visible light is like a stationary bullet
  • Ultraviolet light is like dropped bullet
  • X-rays and gamma rays are like a fired bullet


This high energy ionizing radiation is delivered to the tumor. When the radiation hits the tumor it causes all sorts of damage to the malignant cells, killing a proportion of them by destroying the DNA in the cells.


So now you know a little bit about radiation and malignant cells but how is it delivered to the patient? Can you take a radiation pill? What about a radiation injection?

How is this radiation administered


Radiotherapy can be delivered by injection or pill form, however, this is not very common and is generally only done with thyroid cancers. This is called systemic radiation therapy where radioactive iodine travel in the blood to kill cancer cells in the thyroid. Another method is to place radioactive material close to, in, or near the tumor. This is called internal radiation therapy This type of radiotherapy is called Brachytherapy. Brachy meaning short. It is called short therapy because normally patients will only have between one and three treatments.


The most common method of delivery is from outside the body- this is called external beam radiation therapy (EBRT). An external beam of radiation is pointed at the tumor inside the patient. A patient receiving external radiation therapy may have anywhere from 5 to 38 treatment sessions.


There are a number of different radiotherapy machine that can be used to generate radiation. A linear accelerator is the most common. This is a large machine weighing several tonnes which can rotate around a patient. These machines are very accurate and can rotate to a position within a tenth of a degree and deliver radiation with a positional accuracy of less than 1mm. This is quite impressive given the amount of weight being moved around.


Linear accelerators make radiation electronically. This means that the radiation can easily be turned on and off whenever it is needed. This fact makes them machines safe, as when in a standby mode they produce no radiation at all. This allows the patient to be set up in the correct position. Then the machine is aimed at the tumor and the radiation is delivered to the tumor.


To summarize;

  • Radiotherapy, radiation therapy, radiation treatment area all the same thing
  • They all use radiation directed at tumor cells to kill them
  • The Radiation they use is ionizing radiation- high energy radiation
  • Ionizing radiation comes in several flavours- x-rays, gamma rays, electrons, protons
  • This Ionizing radiation is delivered by several different machines, but most commonly a linear accelerator


And if this didn’t answer your questions, leave a comment, or contact us.