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Dosimetric Characterization of a Prototype Nanotechnology Microbeam Radiation Therapy Device Using Gafchromic EBT2 Film

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R Ger

M Hadsell, R Ger*, C Inscoe, E Schreiber, J Lu, S Chang, O Zhou, University of North Carolina, Chapel Hill, NC

SU-D-144-6 Sunday 2:05PM - 3:00PM Room: 144

Purpose:
Currently there is lack of dosimetry technology for the compact microbeam radiation therapy device we recently developed using field emission based carbon nanotube cathode technology. This is due to the fact that our beam width can be as small as 250μm, restricting the use of normal characterization methods. We demonstrate that with proper calibration and analysis that Gafchromic EBT2 film can be used to characterize our microbeam irradiator for radiobiological mechanistic studies in mice.

Methods:
Our compact microbeam radiation therapy device employs a 160mm x 160um focal line and collimator to deliver an orthovoltage microplanar beam. Specialized phantoms were created to properly measure typical dosimetric quantities including PDD and TMR in addition to other quantities specific to microbeam dose distributions and our source. Gafchromic EBT2 film, cross calibrated earlier to a conventional ion chamber in the uncollimated beam, was used for all measurements.

Results:
While TMR and PDD results for this study were fairly typical, measurements more specific to our source and beam geometry showed unique results. The beam width as a function of distance from the source displayed a steeper increase than would be expected from strictly geometric considerations, probably due to collimator scatter. In addition, the decline in dose with distance from the source was much less severe than expected, as displayed by a linear fit in the tested domain.

Conclusion:
Gafchromic EBT2 film was an excellent choice for the initial characterization of our experimental microbeam device, as shown by the expected forms of the PDD and TMR curves. In addition, the slower drop in dose with distance from the source is consistent with the fact that our device uses a focal line and not a point. Finally, data gathered here will provide a good starting point for a customized treatment planning system specific to our irradiator.

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