Evaluation of the mean incident energy of electron beams measured with a 0.1 ml ionization chamber. Investigation of absorbed dose conversion factor in other ionization chambers

In determining the mean incident energy of electron beams (E-bar0), we have to get parcentage depth dose (PDD) and for this, we also have to spend a great deal of time collecting data and carrying out calculations. Using the water phantom system and the 0.1 ml ionization chamber, if it is possible to calculate E-bar0 according to the JARP protocol, we were able to come up with an efficient calculating system. We have developed an application program for calculating E-bar0 in according to the JARP protocol by taking raw data of the water phantom system, and study calculating the absorbed dose conversion factors of electron beams (CE) in all ionization chambers with mean energy in water (E-bard) and water/air mean restricted collision mass stopping power ratio (L-bar/ρ)w,a of E-bar0. After comparing the measurements between the 0.1 ml ionization chamber, 0.6 ml ionization chamber and shallow ionization chamber, both PDD and E-bar0 agree with the measurement errors. So that it is quite possible to measure E-bar0 by using a 0.1 ml ionization chamber. CE of 0.6 ml and shallow ionization chamber which already had calculated E-bard and (L-bar/ρ)w,a of 0.1 ml ionization chamber show errors within 0.53% as compared with CE of 0.6 ml and shallow ionization chamber. However calculating of CE can not eliminate the physical errors, because the Pf formula is an approximate formula due to the use of (L-bar/ρ)w,a of Δ=10 keV, but we thought that change of CE for fluctuations in E-bar0 could be confirmed. (author)