There is more to proton shielding than meets the eye

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There is more to proton shielding than meets the eye

by Philip F. Jacobus, CEO | October 12, 2015
From the October 2015 issue of HealthCare Business News magazine

 
As you may know, there is a procedure for pouring and curing concrete, and pouring more concrete into walls which are thicker and taller requires more time to pour the concrete and to allow it to cure. Therefore, it is more expensive in many ways. The large mass of concrete also emits a great amount of heat, so thermal cracks can occur in the wall, which degenerates the shielding effectiveness dramatically. In order to prevent this, the concrete has to be of a high grade and specially cured, as well as thoroughly vibrated after the pouring.

PJ: Is the only issue comparing a proton site to a conventional linear accelerator the thickness and quantity of concrete?

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AS: Unfortunately, there is more to it than that, Phil. There are miles and miles of conduit that must be placed inside the frame
of the concrete before the concrete is poured. This conduit is used for cables and water and other components used for the proton system. It is considerably more complicated than a simple linear accelerator. Also, this conduit must turn and bend like a snake to help keep the necessary shielding effectiveness. Multiple bends increase scattering, which is good for shielding purposes. There should be no straight run for the radiation. So, proton walls take much longer, not only because they are wider and higher but because they have a complicated infrastructure inside the walls.
 
PJ: Are there any other factors to consider?

AS: Preparation. We have a saying here in Russia that “he who fails to prepare is preparing to fail.” I can tell you that a lot of thought and prep work has to go in to preparing the areas where the concrete will be poured, even before the concrete is poured. This was so much more time consuming for us than when we poured our linear accelerator or Gamma Knife walls.
 
PJ: What about the floors and ceilings?

AS: According to our regulations here in Russia, we cannot place any areas occupied by the staff below or above the linear accelerator or the proton system. Also, because of the weight of the system, it normally goes on concrete which is on top of the sub floor which rests on earth. Typically, our floors are 6.5 feet thick and so are our ceilings. In every machine we’ve installed, we installed it with the idea that we might someday have to remove it, and much of our equipment has been installed under a roof hatch. Sometimes even stationary cranes may be installed in the technical area of a treatment room in order to be able to maintain or repair the unit in the future.

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