- #1
AndresPB
- 28
- 1
I understand the following image as follows:
There is a build up region that varies with photons energy, the Dmax for 6 MV photons is around 1.5 cm. The build up region means that kerma > dose in that region, meaning that photons are creating electrons and when the Dmax is reached it is going to be the point where the photons make the most electrons and then after this point the dose will begin to decrease because the intensity of the beam (photons) will diminish because of body attenuation.
I am having troubles relating this explanation with the way Optical Stimulated Light Dosimetry and TLD's work. Isn't it suppose that this kind of dosimetry absorb photons to work (Photons excite electrons in the conduction band of the crystal and they move to the valence band)? Then why is it necessary to use some kind of material for the "build up" region to measure dose in surface of a patient?
With this I mean: In many cases, medical physicists use a bolus equivalent of 1.5 cm of water to simulate this "build-up" region and they put the detector underneath it. Why is this necessary if what we are measuring are photons and not electrons?
Thanks a lot!
There is a build up region that varies with photons energy, the Dmax for 6 MV photons is around 1.5 cm. The build up region means that kerma > dose in that region, meaning that photons are creating electrons and when the Dmax is reached it is going to be the point where the photons make the most electrons and then after this point the dose will begin to decrease because the intensity of the beam (photons) will diminish because of body attenuation.
I am having troubles relating this explanation with the way Optical Stimulated Light Dosimetry and TLD's work. Isn't it suppose that this kind of dosimetry absorb photons to work (Photons excite electrons in the conduction band of the crystal and they move to the valence band)? Then why is it necessary to use some kind of material for the "build up" region to measure dose in surface of a patient?
With this I mean: In many cases, medical physicists use a bolus equivalent of 1.5 cm of water to simulate this "build-up" region and they put the detector underneath it. Why is this necessary if what we are measuring are photons and not electrons?
Thanks a lot!