Room: Exhibit Hall | Forum 4
Purpose: Accurate dosimetry in radiobiology studies is very important. While ion chamber is the method of choice for calibration, radiochromic film has many advantages to be used as a dosimeter to measure the dose for each experiment setup. The film calibration can be established using the calibrated orthovoltage irradiator directly, or using MV linac with an energy correction factor applied afterwards. However, there is a disagreement among literatures on the exact value for EBT3â€™s energy response between 50-100 keV. The purpose of this study is to independently determine energy correction factor and compare both calibration methods in terms of uncertainty.
Methods: A Precision XRAD-225 was calibrated with ion chamber following TG61. EBT3 films were irradiated under full back scatter condition on top of solid water blocks to establish calibration curve(kVcalib). Films were also irradiated under a 6MV Linac to establish a separate calibration curve(MVcalib). Energy responses of the film under two beam qualities were determined. Film uncertainties were characterized by a series of irradiation and scanning experiments. The total dose uncertainties from each method were derived.
Results: Our measurement showed EBT3 film has energy response of 0.89 and 0.88 for XRAD-225 with Cu and Al filter respectively which is close to Hammer 2018â€™s value (0.90Â±1.1% and 0.89Â±1.5%). The uncertainty analysis showed that using kVcalib carries 5.2% uncertainty in the dose estimation. The uncertainty using MVcalib is only 3.7%, despite the uncertainty associated with the energy response correction. The difference is due mainly to the higher uncertainty of TG61 vs TG51.
Conclusion: Our results on energy response support Hammer 2018â€™s result. It is recommended to calibrate the EBT3 film with MV Linac and apply energy correction factor for orthovoltage X-ray unit.