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

["John Johnson" <idias@interchange.ubc.ca>]

All



There most be a typo' in the message. I'm not an expert on accelerators,

etc, but how can 26 MeV photons be produced from a 6 MeV electon beam?



_______________________

John R Johnson, PhD idias@interchange.ubc.ca



----- Original Message -----

From: Gary Isenhower <garyi@BCM.TMC.EDU>

To: Vincent A King/KINGVA/CC01/INEEL/US <KINGVA@INEL.GOV>; radsafe

<radsafe@list.vanderbilt.edu>

Sent: Wednesday, April 10, 2002 4:21 AM

Subject: Re: QUESTION regarding radiation theraopy using linear accelerator

thatproduces a 6 MEV photon





>

> 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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