Protons 102 (solving the depth and width problem)

Recapping Protons 101, the unique characteristic of proton beams/radiation (over traditional radiation beams) is that protons can go deeper into the body before they (take your pick):

• "Release their energy"
  
• "Do their work"
  
• "Do their damage"
  
  We remember the chart of the Bragg Peak which shows how deep the protons go at a certain level of Mev. Mev is some measure of the energy of the proton beam. I presume that the "energy" of the proton beam is increased by speeding it up. Remember the terms "particle accelerators", "linear accelerators", and "cyclotrons". All of those speed up particles, and, in this case, protons. Imagine a bullet. If it's going 2 miles an hour and hits your skin, it goes nowhere. At the speed of light, it goes through you and keeps on going for a LONG time. So, speed increases energy.
  
  
  The Loma Linda cyclotron will speed up protons, I imagine, to any speed you want. Maybe like putting your foot on the accelerator. I do know that the protons used for my treatment are going 60% of the speed of light (186,000 mps x 60% = 110,000 mps).
  
  Protons are not like bullets, thankfully, so they won't go all the way through my body at that speed. BUT, the prostate is not shaped like a sheet of paper. If the prostate were paper-thin, the protons need only come at a single speed since the depth from the edge of the skin would be uniform (kinda). So, that paper-thin prostate could get treated/bombarded by a one-size-fits-all proton beam. Said another way, imagine that a proton beam travels at 110,000 mps and does it's work at 10 inches. Fabulous! As long as that paperthin prostate is exactly 10" inside your body and, in fact, is paperthin.
  
  Of course, we all know that the prostate is not paperthin. It is roughly shaped like a walnut. Hmmmm. What to do, what to do? We can't treat just a paper-slice of the walnut. How do we get the proton beam to treat the DEPTH of the prostate? Let's think of some possible ways (from a layperson's point of view):
  

1. Move the proton beam gun away from the body each time, i.e. vary the distance from the body before the beam goes in. BUT, remember the Bragg Peak. The protons only start to release their energy when they hit something solid like the body. Maybe if we move the proton beam a few hundred feet away but that is impracticable.


2. Speed up and slow down the cyclotron so that it gives beams with different energies, i.e. 60% the speed of light plus or minus. E.g. 59%, 58%, 61%, 62% the speed of light. I imagine the depth of the beam would vary at different speeds. (Remember, I am a lawyer and am just imagining the possibilities here -- not a physicist or expert at all!) The problem with this approach is that a cyclotron appears to be a clumsy machine (although very intricate). Unlike a gas pedal on a car, it looks like speeding it up and slowing it down, patient by patient, would be much too complex. For example, there are 3 different treatment rooms at Loma Linda treating 4 patients an hour. That's 12 patients an hour (more or less). It is not realistic to speed up and slow the cyclotron down every 5 minutes. There must be another way.


3. Aha! Perhaps a way to do it would be to have the proton pass through something before it gets to the patient's body that can "modulate" the depth of the proton. If it passes through something first (like a bullet going through an orange first), that can change how far inside the body it goes. And, in fact, that is how it is done. The beam coming from the cyclotron is first passed through a "modulator" wheel. Here is a picture of one. The modulator does two things to the beam. The beam is 1 mm wide coming from the cyclotron. It needs to be spread out to the approximate width of the prostate. The beam comes from the cyclotron, hits the spinning modulator, and that increases the diameter of the beam from 1 mm to much larger -- it is now about as wide as a cannon shell. AND, the modulator absorbs some of the beam to different depths. Notice in the picture that the modulator wheel has openings in it. When the wheel spins, some of the beams will pass unimpeded through these openings. These beams will go to their greatest depths. And, also notice that the modulator wheel has different size/depth "steps" on it. See this close up of the modulator wheel here. The steps are different thicknesses. The beams that hit the thinnest of the steps will go almost to the full depth. The beams that hit the thickest steps will go to the least depth. With different steps, we can then elongate the depth at which the beams in total will go.

Here is a graph of the beams that will go to different depths. Thus, the bomb going into that bunker we have talked about will now explode at a number of different depths, not just one, i.e. at 50', 52', 54', 56', etc. And, rather than just one bomb going in at one spot, there will be a cluster of bombs going in all around the area at different places.

Ok, we have the depth and width problem solved. Rather than a single solitary bomb going in that just explodes at a certain depth and only at one point, we have a carpet bombing where the bombs will explode at a number of different depths. But, we now need to be more precise. We don't want to hit those Crown Jewels we talked about before. Yet, we need to make sure we get all the rooms and tunnels. How are we going to shape the beam bombs to just get what we want them to get?

But, enough for now. Stay tuned for Protons 103.