I’ve made lots of videos on tons of topics, covering the quarks to the cosmos, so to speak.
In this video, I thought I’d tell you something that is way more down to Earth.
I thought I’d tell you about something about a specific kind of radiation therapy, called
proton radiation therapy.
Now before I do that, I should remind you that I am not a doctor.
Well, I am, but as my somewhat curmudgeonly aunt Margaret will often remind me-
Not the kind of doctor that’s good for anything.
Personally, I think that’s a bit unfair, because physics is at least as cool as medicine,
but she does have a point.
I’m not an M.D. Oh yeah- goodbye, Aunt Margaret!
So don’t think that I am offering useful medical advice, because I’m not.
And I’m probably too expensive for you anyway.
Now I don’t want to make light of cancer.
It’s a serious thing.
I’ve lost people I care about to it.
And when we’re talking about it in a real world situation, it’s very, very, very complicated.
But since I’m not the useful kind of doctor, I can simplify things.
Depending on whether a cancer is localized or spread out and intermixed with ordinary
tissue, the real kinds of doctors will operate to try to remove the tumor or do chemotherapy
or maybe use radiation to try to kill the tumor.
So let’s talk about the radiation option.
Traditionally, doctors used gamma radiation to try to kill the tumor.
I made a video on the various kinds of radiation if you’re interested in what that means,
but briefly, gamma rays have no electrical charge and can penetrate deeply into the body.
They’re like x-ray’s bigger and tougher brother.
Now, let’s suppose we have some sort of tumor that is small and compact- say the size
of a marble or so.
Let’s also say that it is buried deep inside the brain.
Because of its location, it might well be inoperable.
Chemotherapy might work, but if it is compact, it might be amenable to using radiation therapy.
So I’m going to talk about proton therapy, but to understand why it is an interesting
approach, I need to talk a little about conventional radiation therapy and its limitations.
So how does it work?
Well, to begin with, conventional radiation is emitted by the source of gamma radiation
and hits the surface of your head.
But what happens as the radiation passes through the tissues of your head?
The way it works is that the tissue near the surface of your head gets the full rate of
radiation and it absorbs some.
As the beam goes deeper, the next layer also absorbs some radiation, but less than the
surface.
That’s because the surface has already absorbed a bit of it.
When the beam arrives at the tumor, it has already been partially absorbed by the layers
closer to the surface.
That means that the surface tissue gets more damage than the tumor itself.
And, of course, the beam doesn’t just stop at the tumor.
It continues on through the brain, and some of it might even come out of the other side
of your head.
The brain tissue after the tumor gets a reduced dose of radiation, but it still gets some.
This picture really illustrates what's going on.
The darker color means more radiation absorption.
The healthy surface tissue gets the most dose and therefore is most likely to be damaged.
So that sounds kind of awful.
The cancer only gets part of the radiation dose and healthy tissue gets more than the
cancer does.
So how do doctors handle this?
Well, the way they do that is they move you or the beam so the beam goes through a different
path through your head.
That way, one treatment hits one spot on your head’s surface, while the next treatment
goes through another.
However, every treatment goes through the tumor.
Over the course of multiple treatments, the tumor gets hit again and again, with the other
tissues getting hit only once.
The goal is that the cumulative dose in the tumor is higher than the other tissues receive.
It’s actually quite clever.
Now what about proton therapy?
How does that work?
Well, unlike gamma rays, protons have electrical charge.
They’re also heavy, at least as far as subatomic particles go.
And, when they pass through matter, they lose their energy fairly slowly for most of the
passage, but then lose a whole bunch just at the end.
This is called the Bragg peak if you want to look it up.
It’s kind of like when you’re slowing your car down for a stop sign.
It’s smooth going until the moment when the car actually stops and then the back of
the car settles down and you get a bit of a jerk.
We can see in this image what this means in terms of energy dose.
Here, the surface tissues receive a lower dose than the tumor does and, further, the
beam doesn’t continue on through the head.
So this sounds like a great approach.
And, of course you can do the trick of shooting the beam at the tumor at different angles.
This means it is possible to hit the deep tumor hard, with much less damage to surrounding
tissue.
Now, proton therapy isn’t a new idea.
The first paper on the subject was written by Robert Wilson in 1946 when he was developing
a cyclotron accelerator at Harvard.
Robert Wilson also built Fermilab, the laboratory at which I am a scientist.
Wilson was like totally the bomb.
The Harvard cyclotron collaborated with Massachusetts General Hospital and developed the technology
over the next 40 years or so.
The first commercial and hospital-based facility began in 1989 at the Clatterbridge Center
for Oncology in the UK, followed by one at the Loma Linda University Medical Center in
1990.
That particular accelerator was built at my own Fermilab and one of my fellow graduate
students moved there to operate it.
Small world.
Proton therapy centers are becoming common around the world.
In fact, there’s one just a few miles from Fermilab.
I’ve even used it to irradiate electronics to see if they would work in a high radiation
environment.
Now, I want to remind you that I’m not an M.D. and I’m not a radiation therapy specialist.
So don’t take any of what I’ve said as medical advice.
For that, you need to talk to a real oncologist or a radiation expert; specifically, one of
those kinds of doctors who actually is useful.
Proton therapy is really pretty cool.
It causes less damage to surrounding tissue than conventional gamma ray radiation and
it's becoming useful to treat a variety of tumors.
While I hope that neither you nor anyone you care about ever gets cancer, it unfortunately
does happen sometimes.
If you are in that awful situation, maybe it makes sense to, like the television medical
commercials say-
Ask your doctor if proton therapy is right for you.
So like Aunt Margaret said, I’m not the best source of medical advice, but the underlying
physics is really super interesting.
If you liked the video, be sure to like, subscribe and share.
Let's get those numbers up.
And let me know what you think in the comments.
See you next time, and keep on physics-ing.