Re: QUESTION regarding radiation theraopy using linear accelerator thatproduces a 6 MEV photon

[Gary Isenhower <garyi@BCM.TMC.EDU>]

I think the primary question was about the 6 MeV energy.  It was chosen

for its depth dose curve.  Because of build up, the dose peaks at some

depth in the tissue which varies with the energy.  The idea is to

maximize dose to the treatment volume while sparing skin and surrounding

tissue.



I am familiar with one series of linacs.  A wave guide accelerates

pulsed electrons toward an "energy selector" consisting of a strong pair

of tunable electro magnets.  Like a cyclotron (or a prism), the electron

pulse curves and spreads according to energy.  The desired energy is

then selected by collimation.  The remaining semi mono energetic

electrons can be used directly for very shallow treatment depths or they

can be directed at a thin target to generate photons with a very small

scatter angle (i.e. about the same vector as the incident electrons). 

The resulting photons are nearly mono energetic and can be 26 MeV or

higher.

    _______________________________________________



	Gary Isenhower

	713-798-8353

	garyi@bcm.tmc.edu

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