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Calibration and Comparison of Dosimetry Systems Used in the Therapeutic Soft X-Ray Energy Range

S Souri

S Souri*, X Qian , Y Chen , A Jamshidi , North Shore Long Island Jewish Health System, New Hyde Park, NY


PO-BPC-Exhibit Hall-22 (Saturday, March 5, 2016)  Room: Exhibit Hall

The main objective of this study is to compare and evaluate different dosimetry systems which can be used as in vivo-dosimetry for intraoperative radiotherapy in therapeutic soft x-ray energy range.

Optically stimulated luminescent dosimeter(OSLD)nanoDots and radiochromic-EBT2 films evaluated in soft x-ray energy produced by a Zeiss-Intrabeam 50 kV radiotherapy system using 4cm surface applicator. Solid water with different thicknesses used to simulate different depths. NanoDots irradiated in depths of 3mm, 10mm and 20 mm while EBT2 films at surface and 20mm depth.The responses of the nanoDots were measured by a LandauermicroSTAR-ii reader system.For film dosimetry, an Epson scanner and RIT software used.

The nanoDot response in soft x-ray energy was observed as big as a factor of 4 compared to that for 6 MV photons.In contrast, the EBT2 film OD in 50 kV drops a factor of 3 compared to that in 6 MV and is less than 0.05 below 50 cGy.In order to achieve a calibration accuracy of 3%, segmented linear calibration curves were used. The calibration curves yield nearly identical results for nanoDots at depths of 10 and 20mm while about 15% less at 3 mm depth, suggesting that the nanoDot sensitivity increase with increased x-ray energy and reach a plateau for harder x-ray beyond 1 cm water equivalent depth for 50 kVp x-rays. However,For EBT2 films, OD at 2 cm depth increases about 25% with respective to that at surface, demonstrating slightly larger energy dependence than nanoDots.

The nanoDot OSLD is a better system for use in soft x-ray energy with greater sensitivity and less energy dependence compared to EBT2 films.Caution should be exercised in choosing an appropriate set of calibration when x-ray beam hardening effect has to be taken into consideration. More detailed energy dependent effect for the nanoDots is under investigation.

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