Every once in a while heavy particle radiation makes it back in the news, but it has lost favor with many hospitals because of the size of the accelerators. Most accelerators that are currently being used emit photons and/or electrons. The heavy particle accelerators emit either protons or neutrons. An electron is ~ 1000 times lighter than protons or neutrons, so they are much easier to accelerate. neutrons due not have charge, so the way that neutron beams are created is by colliding protons into the (although we are dealing with subatomic particles and quantum physics rule this domain, general mechanics of equal mass collisions are still a good approximate). Getting back to the size issue, an electron (linear) accelerator can fit in a room easily, but a proton accelerator is the size of a small building.

The metal masks that you speak of are called blocks and are usually made of cerrobend.


Now to answer your questions:

1. The setup and treatment of total body irradiation is more complicated than taking a CT and building the filters that are required. BUT on a theoretic basis, yes you are correct, a continuous distribution would be best. BUT we do not live in a theoretical world. We have to look at complicity and cost v.s. gains. For TBIs, we are not treating cancer, we are trying to suppress the immune system to prepare the body for a transplant. It is not crittical to get absolute even dose over the entire body +/- 10% works fine.


2. I think that #1 answers this, we are looking to correct gross changes. Also the beam enters the patient laterally (through the side), so imaging that you could see that it does become a 2d problem.


3. Yes, these thread can die quickly, but then again there are threads that seem to never end. It all depends on the intrest level, and the area of the question. As far as burning the patient, we take every precaution to ensure that the patient is not mistreated. Currently this involve painstaking measures of creating the filters 4-6 hours per patient. We also take extreme care in the setup so that there are not any light leaks. That being said, we are changing the way that we make the blocks from a column type to a pyrimid type, and I am trying to write some software (as a tool) to quickly figure out the best way to do this. It is easy to do by hand, but can be time consumming. The software will only be a tool, and every thing that we do will be checked and double checked.



Thank you everyone for your ideas and comments!

In reply to Re^2: Finding the simplest combination of descrete thicknesses that sums nearest to the target thickness. by doowah2004
in thread Finding the simplest combination of descrete thicknesses that sums nearest to the target thickness. by doowah2004

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