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SU‐E‐T‐95: Impact of Chamber Support Device On In‐Air Profile Scans of High‐Energy Electron Beams
Author(s) -
Khan A,
Narra V,
Yue N
Publication year - 2013
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4814530
Subject(s) - ionization chamber , dosimetry , monte carlo method , materials science , cathode ray , beam (structure) , dose profile , optics , electron , nuclear medicine , physics , nuclear physics , ion , mathematics , medicine , statistics , quantum mechanics , ionization
Purpose: In‐air profile measurements are required for co mmissioning the Electron Monte Carlo Algorithm in Eclipse (Varian Medical Systems, Palo Alto CA). The purpose of this study was to investigate the impact of the ion chamber support device on in‐air profile scans of high‐energy electron beams. Methods: An IBA Blue Phantom 2 with CC13 (IBA Dosimetry, Germany) ion chamber was used to reco rd in‐air one‐dimensional profiles of electron beams from a Varian Clinac 21EX with no applicator and co llimator jaws set to maximum opening (40cm). The chamber was set at 95cm from the source using the ODI and lateral movement verified to be level. Due to the large field size, only half profile scans were obtained.A chamber support device was manufactured using rigid foam and attached to the chamber holder included with the tank. This relocated the chamber to approximately 25cm away from the metallic crossbar and plastic chamber holder. Profile scans were co llected for all available beam energies (6MeV, 9MeV, 12MeV, 15MeV, 18MeV) both with and without the use of the additional foam support. Results: Measurements with and without the use of the foam support device resulted in minimal change to the reco rded plots. For profiles normalized to CAX, the mean absolute difference between co rresponding points along the profile was found to be less than 1% for all energies measured. The maximum deviation at any point was less than 1% for all but two energies (9MeV=3.5%, 15MeV=4.5%). The difference at 80% of the field size was less than 1.5% for all energies. Co nclusion: The ion chamber support device included with the IBA Blue Phantom2 appears to have minimal impact on in‐air profile measurements for high energy electron beams. Additional air‐like support material should therefore not be necessary for measuring such profiles.