You will remember from Protons 101 and 102 (see prior posts) that we solved the "realease the energy inside the body rather than on the exterior" problem and that we solved the problem of getting depth with proton treatment (so that we can treat a 3D object -- the prostate-- rather than a 2D object). Now, let's get personal. I want that damn beam to treat MY prostate -- not be shaped to Joe the Plumber's prostate. Prostates come in slightly different sizes (but, bigger is not better for this part of the anatomy) and shapes so, let's get it to fit ME.
There are two devices that do that. The first is known at the "aperture". You see my aperture
below or nearby. This is the hole in the middle of that heavy metal object (lead?). It is designed to fit the silhouette of my prostate. The proton beam hits the lead aperture and stops where there is lead but keeps going where the hole is. On to my prostate. Very nice. But, what keeps the beam from going beyond my prostate after it hits it? This may be confusing, because in Protons 102 we talked about how the beam got its depth. That depth, however, gave it a uniform depth of, say, 2". So, if we were treating a perfect cylinder, that would be great. But, we're not. We need to treat an irregularly shaped object. The aperture gets the silhouette shaping. The 2D shaping. But how do we get the 3D shaping? How do we treat what we need to treat but have it stop where the prostate has little depth (around the edges) but keep going where it has greater depth (in the middle). The answer is the "bolus".
The bolus is a wax-like object. There is a picture of one below. After the beam goes through the aperture, it then goes through the bolus. The wax-like bolus approximates the human body (it is an average of human tissue -- muscle, fat, senews, etc.). Remember that the proton beam goes a certain distance through the body. If it has more body to go through, then it won't go as far. That is what the bolus does -- acts as a faux human body to vary the depth of the beam. The bolus is
made up of different depths of wax -- see the sample. After the beam goes through the aperture, it is shaped to my prostate. Then it goes through the bolus and will "release its energy" at the appropriate depth for MY prostate. There is more to this than described -- but you get the essential picture. Take a look at this Loma Linda video for a simple view of how it works. You have to wade through most of the video, and it's pretty simplistic, but it may help: http://www.protons.com/proton-therapy/proton-videos/treatment-preview.html . The most important aspect of this video is that it shows you, about 3/4 of the way through, how the bolus is made. There is no description of the function of the bolus or how it works, but at least you know now from this post how it's done.
There are two devices that do that. The first is known at the "aperture". You see my aperture
below or nearby. This is the hole in the middle of that heavy metal object (lead?). It is designed to fit the silhouette of my prostate. The proton beam hits the lead aperture and stops where there is lead but keeps going where the hole is. On to my prostate. Very nice. But, what keeps the beam from going beyond my prostate after it hits it? This may be confusing, because in Protons 102 we talked about how the beam got its depth. That depth, however, gave it a uniform depth of, say, 2". So, if we were treating a perfect cylinder, that would be great. But, we're not. We need to treat an irregularly shaped object. The aperture gets the silhouette shaping. The 2D shaping. But how do we get the 3D shaping? How do we treat what we need to treat but have it stop where the prostate has little depth (around the edges) but keep going where it has greater depth (in the middle). The answer is the "bolus".The bolus is a wax-like object. There is a picture of one below. After the beam goes through the aperture, it then goes through the bolus. The wax-like bolus approximates the human body (it is an average of human tissue -- muscle, fat, senews, etc.). Remember that the proton beam goes a certain distance through the body. If it has more body to go through, then it won't go as far. That is what the bolus does -- acts as a faux human body to vary the depth of the beam. The bolus is
made up of different depths of wax -- see the sample. After the beam goes through the aperture, it is shaped to my prostate. Then it goes through the bolus and will "release its energy" at the appropriate depth for MY prostate. There is more to this than described -- but you get the essential picture. Take a look at this Loma Linda video for a simple view of how it works. You have to wade through most of the video, and it's pretty simplistic, but it may help: http://www.protons.com/proton-therapy/proton-videos/treatment-preview.html . The most important aspect of this video is that it shows you, about 3/4 of the way through, how the bolus is made. There is no description of the function of the bolus or how it works, but at least you know now from this post how it's done.
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