Dose Rate and Energy Dependence of EBT, EBT2, EDR2 Films, and Mapcheck2 Diode Arrays in Beam Profiles From a Varian TrueBeam System
S Oyewale*, S Ahmad, I Ali, Oklahoma Univ. Health Science Ctr., Oklahoma City, OKSU-E-T-85 Sunday 3:00:00 PM - 6:00:00 PM Room: Exhibit Hall
Purpose: To investigate the dose rate and energy dependence of dosimetric systems radiographic film (EDR2), Gafchromic films (EBT, EBT2), and MapCheck2 diode system, using regular and flattening-filter-free (FFF) profiles from a Varian TrueBeam system.
Methods: EBT, EBT2, EDR2 films and Mapcheck2 were exposed to open field regular beams with energies 6MV, 8MV, 10MV and 15MV and FFF beams of 6MV and 10MV on the Varian Truebeam accelerator. A field size of 20cm x 20cm was used and the films were placed at the depth of dose maximum for the various energies. The MapCheck was setup to measure profiles at 5 cm depth for all energies. Profiles measured with ionization chamber were used as a reference. Dose profiles from regular beams were used to investigate energy response effects where the beam is hardened in the center relative to the edges. While, dose profiles from FFF beams were used to investigate dose rate effects.
Results: The profiles from EBT and EBT2 films relative to chamber showed gradually increasing energy response from center of the beam (2%) towards edges (10%). The profiles from EDR2 film showed no energy response in flat profile regions, however, there was increased energy response (8%) in the penumbra region. MapCheck2 profiles showed an increasing energy response (3%) at the edges of the beam. The energy response showed small dependence on beam energy (4%). Profiles from the different films and Mapcheck2 showed negligible dose rate effects (2%) for the profiles from flattening-filter-free beams for all energies and the dose rate effects where 2% was uncertainty due to cumulative errors of scanner reproducibility and film stability.
Conclusion: The EBT, EBT2 films showed stronger energy response effect compared with EDR and MapCheck2. The dose rate effects in the profiles from FFF beams were negligible in the previous four dosimetry systems.