Diagnostic x-ray added filters

[schaaf_d@kees-sg01.kee.aetc.af.mil]

I would like to request assistance in finding a book or article explaining 
when & why to use the additional filters that are available to be inserted 
in the beam on our new Toshiba diagnostic units.  There are three levers in 
the tube housing which can position 1.5mm AL, 1.5mm Al & .1mmCu, and 
1.5mmAl & .2mm Cu ( and combinations of these) into the beam.  I have not 
found anything in the manuals or reference books on what type of 
exams/patients these would be beneficial.   The tube is reasonably well 
filtered without any of these in (I measured 2.86mm Al HVL @ 80kVp).  The 
x-ray tech supervisor tells me that they removed the "wheel" style of 
additional filters that were on the units replaced by the Toshibas because 
of occasional mysterious light films.  Are these filters worth keeping or 
are they an additional source of repeat films (& more dose to patients) for 
our student techs?  Thank you in advance for your expertise.

Nick Schaaf, Capt, USAF, BSC
81 Diagnostics and Therapeutics Squadron
Keesler AFB
(228) 377-7390
schaaf_d@kees-sg01.kee.af.mil