AbstractID: 6611 Title: Fluence and wall correction factors for parallel-plate ionization
chambers for electron beam calibrations in the TG 51 protocol
The new AAPM TG 51 protocol for electron beam calibration makes some assumptions
that should be investigated regarding the correction factors for parallel-plate ionization
chambers in an electron beam. These include the fluence correction factor, Pfl, the wall
correction factor, Pwall, and a possible correction factor due to the backscatter from the
chamber back-wall. Due to the difficulty in separately measuring Pwall and Pfl the product
pq = PwallPfl is measured. To study these effects, four commonly used parallel-plate
chambers and a cylindrical chamber are used to measure the output for 6, 9, 12, 16 and 20
MeV electron beams following the protocol. The cylindrical chamber having a
ND,w(60Co) calibration factor obtained from an ADCL is used to obtain [kecalND,w(60Co)]
values for each of the parallel-plate chambers following the protocol. Since each of the
parallel-plate chamber’s entrance windows and sidewalls are constructed from different
materials, by intercomparing the different chamber measurements some conclusions can
be inferred regarding these assumptions made in the protocol. Additionally, these results
will also provide information on the consistency of the protocol for electron beam
calibrations. A discussion of the results will be presented.