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Physics/Can a beam of light, or Gamma Knife beam pass through a hole as small as 0.1mm, which is as thin as a human hair.


QUESTION: The Gamma Knife uses a Cobalt 60 source to create beams of Gamma Rays to destroy tumors in the brain, I want to see how small these beams can be reduced in size.
Light, and Gamma waves are part of the Electromagnetic spectrum.
I cannot insert drawing diagrams in here, if you can imagine a Cobalt source, or light source from the left, and all the Gamma Knife beams, or light beams were being fired from from the left into a funnel shaped object to the right.
So all the beams were going into the funnel, and as the funnel gets more narrower going to the right, there is a pipe with a 0.1mm hole, so all the Gamma Knife beams are being forced into the small hole, could all the Gamma Knife beams make it through.
Can a Gamma Knife beams be made so small that it could target a group of neurons in the brain around 0.1mm or smaller which is around 1000 neurons.
Can a Gamma Knife beam be made smaller than 0.1mm.
Thank you for your help with this question.

ANSWER: You can actually insert diagrams here, but here's what you need to know:

1)  Gamma rays of that high an energy (1.173 and 1.332 MeV) from 60Co have a far shorter wavelength than the space between atoms.
2)  You can shadow a source emitting spherically in all directions, but never fully shield it.  But you can get close enough that it doesn't matter.
3)  Funnel-shaped objects do not funnel light.  Light travels in straight lines.  The 0.1mm hole will work through thick enough lead (or other dense material) to collimate the radiation into a beam with a minimal spread, if the collimator is thick enough.
4)  It's impractical to collimate as tightly as you're talking about, the sources would be ridiculously hot to give you enough gamma beams to do any good at all.  

Basically, you can make a gamma knife smaller than 0.1mm.  If you have a zillion super-hot sources that would cost you billions of dollars with shielding and aiming to make it work.  Aside from  There's a reason that gamma knife machines need to have over 200 gamma sources inside them and already have very small collimators.  To go beyond that, voxel-size (they affect volume "pixels" called "voxels"), they would not only escalate cost and would be the bitter limit of our technology to aim them any more finely than that.  At that point, where you're dealing with sub-millimeter sizes, you're better off with something like boron neutron therapy or chemo.  And by a long ways.

---------- FOLLOW-UP ----------

Gamma Knife idea
Gamma Knife idea  
QUESTION: Great, thank you very much for your answer. I am going to send you mt idea for the Gamma Knife, that I have sent to some Universities, can you give some feedback on the idea, do you think it will work.
There are two things stopping this idea from working,
1. Gamma Knife beams cannot be fired through a hole 0.1mm or smaller.
2. Gamma Knife beams cannot affect groups of neurons at the 0.1mm scale becuse there is not enough dose.
Also can you answer this new question.
Do all elements in the periodic table of elements all make the same strength gamma waves. if some elements can make stronger Gamma Knife beams, that going to help this idea work better.
Thank you very much for all your help.
I am going to send each document one page at a time, because I cannot send the whole documents at once.

OK, no, this is exactly the wrong idea.  There are several problems with this design.  I think your fundamental flaw is the way you drew the second page's picture.  Gamma rays are not like optical light, they need thick lead shielding to stop them.  They don't just stop right at the surface of lead, there's an exponential decrease of the number of them that penetrate lead as you increase its thickness.  You can't just use successively thinner pipes for collimation, you need to start with a thin pipe to begin with and deal with the spread of the beam that makes it to near the end of the pipe, where the gamma rays have a better chance of getting through the lead and into parts of the patient where you don't want them to go.  

Next, you're reducing the number of beams.  The point of all those beams is that the tissues they go through will receive far less dose and radiation damage than where they all cross.  That means that your design with 1/10th the number of beams will give the tissue where they must penetrate 10 times the dose of the current design in order to deliver the same dosage to a tumor.  More, if you consider more advanced design considerations for killing larger tumors.  We need more beams, not less.

After that, your design for shielding is the opposite of what you want.  You want an absolutely solid shield, with only holes drilled in it for maximum shielding.  Again, the more lead or depleted uranium you have for shielding, the better.

Fourth, imaging techniques can't image a tumor as accurately as you're wanting, and patients move a little even when strapped in.  It's impractical to deliver doses to submillimeter volumes of tumor this way, and it's the wrong way to go from a safety and design standpoint.  It's also hard to make sources that would be so small and hot enough to use, but still handle them safely and accurately.

In the end, you want the beam to encompass the entire tumor if you can, from as many directions as possible.  Ideally, the best way to improve on gamma knife design would be to design custom shields, perhaps with a 3D printer, and print each patient their own gamma knife...then recycle the lead in the 3D printer between patients.  But I don't know of anyone willing to go to that kind of expense.


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Dr. Stephen O. Nelson


I can answer most basic physics questions, physics questions about science fiction and everyday observations of physics, etc. I'm also usually good for science fair advice (I'm the regional science fair director). I do not answer homework problems. I will occasionally point out where a homework solution went wrong, though. I'm usually good at explaining odd observations that seem counterintuitive, energy science, nuclear physics, nuclear astrophysics, and alternative theories of physics are my specialties.


I was a physics professor at the University of Texas of the Permian Basin, research in nuclear technology and nuclear astrophysics. My travelling science show saw over 20,000 students of all ages. I taught physics, nuclear chemistry, radiation safety, vacuum technology, and answer tons of questions as I tour schools encouraging students to consider careers in science. I moved on to a non-academic job with more research just recently.

Ph. D. from Duke University in physics, research in nuclear astrophysics reactions, gamma-ray astronomy technology, and advanced nuclear reactors.

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