Eli5 How does radiation therapy actually work? Like how doesnt it break down more of the body and make the cancer worse or something like that? And does it target only cancer area or everything?
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Generally, radiation treatment focuses ionizing radiation into a narrow beam and directs it to the tumor along a path that transits the least amount of healthy tissue possible. By targeting a tumor from multiple directions in successive exposures, you maximize the radiation that passes through just the tumor while minimizing the radiation that any other specific area of healthy tissue receives.
Hitting the tumor from multiple directions is the key to minimizing adverse effects from radiation on surrounding healthy tissue.
Almost all cancer therapy does precisely one thing. Destroys the tissue that’s cancerous.
Whether you burn it, poison it, cut it out, radiate it, chemically dissolve it, whatever… that’s the only way to “treat” cancer once you have it. You just hope that the surgeon lasered / scalpelled / incinerated / poisoned / radiated / amputated enough of it so that it does regrow.
Cancer is basically one of your own cells reproducing uncontrollably and never getting the “STOP!” signal from its DNA, etc. All your cells multiply all the time, but they know when to stop. When the “STOP!” signal gets corrupted (by old-age, radiation, random mutation, carcinogenic substances, etc.) that ordinary skin, blood, brain, or whatever cell turns into cancer… it just keeps reproducing. And the things it produces also have that same error. So you started with one cancerous cell. And now you have 2. No, 4. No, 8. 16. 32.. fuck sake’s, 64…
There is no real way to get EVERY one of those cells and get them to ALL stop reproducing. And you only have to miss ONE CELL for the cancer to return.
Thus almost all cancer treatment after diagnosis is based about trying to contain it, remove it and destroy it all… including surrounding healthy tissue. Because you just can’t take the chance that you missed a bit of it. So you cut it out, and everything around it, with a nice large safety barrier that you remove from healthy organs, tissues, etc. too in order to make sure you capture all the cancerous cells.
Radiation therapy does it by literally aiming radiation at the tumour. Radiation kills things. Aimed at the cancer, it kills the cancer and the surrounding tissue. Voila. With any luck, cancer gone. Chemotherapy poisons it. Surgery cuts it out or chops off that part of your body entirely.
All of modern medicine – and some parts are very high-tech even in cancer treatment such as the drugs, etc. – is inferior to basically just burning/cutting/removing the cancer and stuff around it.
P.S. You have cancer right now. So do I. So does everyone. Dozens of times a day, a cell somewhere goes cancerous in your body. But the body’s immune system detects it, tags it, destroys it itself. You get *diagnosable* cancer when the body fails to do that. Some treatments revolve around trying to make the immune system see the cancer (but it’s already missed it, because it’s literally PART OF YOU that’s cancerous and it doesn’t want to attack you!). Some treatments involve killing off your immune system because it’s making the problem worse or getting in the way or a side-effect of the treatment (e.g. chemotherapy).
But cancer is an inevitable consequence of being a cell-based lifeform. If you don’t die of anything else, you’ll die of cancer eventually. Because you’re getting it all the time, and it’s only when your body fails to notice that something is cancer that it becomes a problem.
But all of modern science – as amazing as that is – is practically inferior to chopping the cancer out of you, burning everything around it, and poisoning the entire area in the hope that you’ll kill off the cancer without killing off too much of you.
Radiation gets absorbed by tissue, but the amount of energy absorbed is uneven. Most of the energy released by radiation and absorbed by the body is focused in a very specific point. There is barely any damage before that point and the ray doesn’t go past it, so there is no damage after. By adjusting the distance the radiation travels and the direction it comes from, they can specifically target very small areas and destroy cells there. There is some damage to other tissue as well, but I’ve heard from patients that it’s just like a sunburn.
If you imagine a strong laser, the point where it gets absorbed is the surface of the skin, so it burns there. Targeted radiation therapy works in a similar way, the main difference is that it passes through some of the body before it releases its energy, so it can burn inside without much damage on the way
Radiotherapy only target the cancer area.
It’s strong enough to kill most cells that are dividing in the area.
Weak radiation increases the quantity of mutation and therefore the risk of cancer. Strong radiation kills the cells.
Radiotherapy affects plenty of healthy cells too, but since most of your cells aren’t rapidly dividing once you’re an adult, you’re mostly fine. You still get a lot of secondary effects from healthy cells dying.
Radiographer here! I have over 5 years of experience working in radiotherapy. I will try to describe how a certain type of widely used radiotherapy works technically.
To clarify, a radiologist is, broadly speaking, a doctor who looks at medical images and diagnoses things. A radiographer is, broadly speaking, the technician operating medical imaging machines and taking the scans. I work as the latter, but no longer in radiotherapy.
I will briefly describe intensity-modulated radiotherapy, which is one type of several, but probably one of the most common these days.
For a patient to receive this form of radiotherapy, they must first have a type of CT scan taken. CT scans are useful for several things, but very simply, they give us a picture of stuff in your body, and they also tell us how dense those things are (obviously, bone is going to be more dense than liver tissue, for example). The imaging is done in “slices” so that you scan scroll through them, and look at the body from different angles.
Using this CT scan, a radiotherapist doctor will basically draw the target area for the radiotherapy, which is usually most of the tumor tissue. They will also draw a surrounding “safety” zone, in case the patient or the tumor moves a little during the time the radiation is administered. Also, they’re going to draw the critical organs that must receive as little radiation as possible. This can look like this image:
[https://bmccancer.biomedcentral.com/articles/10.1186/s12885-017-3144-5/figures/2](https://bmccancer.biomedcentral.com/articles/10.1186/s12885-017-3144-5/figures/2)
Next, a specially trained medical physicist will make a treatment plan. They do this using special software that can take the info from the CT scan (like tissue density), and calculate how best to deliver the radiation, so that most of it will be delivered to the target area, and least of it to the tissues we want to protect.
Once that’s done, the treatment can begin. The radiation can be delivered in a single occasion, a few occasions, or spread over many occasions (sometimes even 30+ days). This depends on many factors that the doctor responsible for the treatment must be familiar with. There are protocols for different types of tumors in different parts of the body.
An average linear accelerator, machines used in radiotherapy, might look like this:
[https://www.medicaldevice-network.com/wp-content/uploads/sites/23/2019/07/1l-Image-TrueBeam-Radiotherapy-System.jpg](https://www.medicaldevice-network.com/wp-content/uploads/sites/23/2019/07/1l-Image-TrueBeam-Radiotherapy-System.jpg)
The patient lays the table. Remember the CT scan that was taken before, the one necessary for the plan? The technicians will have marked the patient (using tattoos, or small metal markings, for example), creating a reference point. This point is important for many reasons; one is that it lets the radiotherapists position the patient before therapy. Then, the machine will move this table according to the treatment plan.
After this, the technicians will use the linear accelerator to take another CT scan. This one is kinda worse than expensive diagnostic CTs, but its only use is to give us a lower resolution image of the body to make sure we position the person correctly. The technican then sorta “overlaps” this new CT with the old one, checking the patient’s anatomy and matching their current position on the table to the plan position. If you do it well, the patient should be laying on the bed exactly as they were when their initial CT scan was taken. So now we know the radiation will go to the right spot. So, we take a new picture, and make sure the new picture and old picture match up.
Then, the radiation source, the big head of the machine, will start rotating. In this head is a series of individual “leaves” of highly dense material, usually tungsten, which move independently using little motors. These are so dense that they block most of the radiation if they are all closed. They can form shapes to allow radiation to pass through. The software and machine take the plan created by the physicist, and start moving these leaves in a way that, combined with the rotating head of the machine, will mean that the tissue surrounding the tumor will receive less radiation than the tumor itself. It looks like this:
[https://www.youtube.com/watch?v=msX1ypCjkK4&ab_channel=PhoenixCyberKnife](https://www.youtube.com/watch?v=msX1ypCjkK4&ab_channel=PhoenixCyberKnife)
This lasts a few minutes, and then, you’re done. For the day, at least.
Note that it’s not possible for the radiation not to go through surrounding tissue. For example, if you have a lung tumor, some of it will have to go through your skin, ribs, surrounding lung, even your heart. But because the radiation source is constantly rotating around you, and the leaves of tungsten constantly moving, you can effectively minimize how much radiation reaches critical parts of your body.
That is one type of radiotherapy, but there are many others.
The other responses have covered why radiation works against cancer cells, and does less damage to normal cells.
So I’ll mention a neat “trick” about radiation. Say i throw radiation through you, I’m essentially shooting particles at you. You’d think that anything in the path of my “bullet” would be disintegrated, right?
But really, the faster the bullet is travelling, the *less* likely it is to actually hit anything (but when it does, it packs more of a punch).
So you can play this to your advantage, and send the bullet at *just* the right speed that it misses most of the things in your body, until it happens to be right where you want it, and then it hits.
It’s not exact, but as mentioned with other comments, you take a lot of “good enough”s and add them together to get a “pretty decent”.
There are already a lot of good answers. I thought maybe you’d be interested in this video from kurzgesagt/in a nutshell about how your own body fights cancer. It touches on some things that have been explained here.
The short version: they are hoping the treatment kills the cancer before killing you. It is dangerous to you, but they give you them if the risk of the cancer doing harm is greater than the treatment.
This is also the thinking underlying chemotherapy, which is important to keep in mind. Since cancer cells divide rapidly, they are an easy target for these medications, but other rapidly replicating cells, such as those in your digestive tract, are also killed.
I had testicular cancer in 2003 and when i got bowel cancer in 2019 the nurses said they thought it was most likely the radiotherapy treatment from the first bout that caused it. They see lots of cases but sadly, the data hasn’t been collected historically in such a way that we can learn from it so all we have is anecdotal knowledge from their experience.
Also noted a link between depression and cancer too but again. No supoorting data yet.
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