SU-E-T-244: High Spatial Resolution EBT2 Film Dosimetry

The purpose of this study was to measure depth dose curves and dose effects near high-Z interfaces with radiochromic EBT-2 films reaching a spatial resolution superior to conventional methods with no quality losses.

The setup is made of two 12cm stacks of RW3, fixing an EBT2 film in a vertical position. To measure a depth dose curve, the setup was irradiated with a 15MV photon beam (Siemens Primus). Since the film is positioned parallel to the beam propagation, the depth dose curve is measured with only one film per depth. Additionally, a dental gold alloy probe was inserted in the RW3 stack at 6cm depth and the dose enhancement in front of the probe was measured with the method described above. Hereby, the bottom edge of the film touches the probe's surface.The irradiated films were digitized with a resolution of 72dpi using an Epson 10000XL flatbed scanner with a transparency unit and alignment frames. With this setup, the spatial resolution is only limited by the scanning resolution.

In order to verify the new measurement method, comparisons of the measured depth dose curves with the conventional method of placing the film orthogonal to the beam propagation showed deviations of lesser than 3%.The comparison of the dental gold measurements with Monte Carlo simulations shows a systematic lower measured dose which is still within 5% consistency. However attention has to be paid in the experimental setup and film preparation.

The introduced method shows significant advantages to conventional orthogonal EBT2 film positioning. It shows a very high spatial resolution and the area of interest is only limited by the film size. The method will be used in further studies, to investigate dose profiles and dose effects near interfaces and in inhomogeneities.