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Characterization of the New Xoft Axxent Electronic Brachytherapy Source Using PRESAGE Dosimeters

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A Steinmann

A Steinmann1*, J Adamovics3 , D Followill4 , G Ibbott5 , (1) UT MD Anderson Cancer Center, Houston, TX,(2) University of Wisconsin - Madison, Madison, WI, (3) John Adamovics, Skillman, NJ, (4) UT MD Anderson Cancer Center, Houston, TX, (5) UT MD Anderson Cancer Center, Houston, TX


SU-E-T-171 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To characterize the Xoft Axxent electronic brachytherapy source using PRESAGE™ dosimeters to obtain independent confirmation of TG-43U1 dosimetry values from previous studies and ascertain its reproducibility in HDR brachytherapy.

Methods: PRESAGE™ dosimeters are solid, polyurethane-based dosimeters doped with radiochromic leucodyes that produce a linear optical-density response when exposed to radiation. Eight 1-kg dosimeters were scanned prior to irradiation on an optical-CT scanner to eliminate background signal and any optical imperfections from each dosimeter. To quantify potential imaging artifacts due to oversaturated responses in the immediate range of the source, half of the eight dosimeters were cast with a smaller channel diameter of 5.4 mm, and the other half were cast with a larger channel diameter of 15mm. During irradiation, the catheters were placed in the center of each channel. Catheters fit the 5.4mm diameters channels whereas polyurethane plugs were inserted into the larger channels to create a sturdy, immobile catheter which allowed uniform dose distributions. Two dosimeters of each 5.4mm and 15mm were irradiated at either 1517.3 cGy or 2017.5 cGy. Post-irradiation scans were performed within 48 hours of irradiation. A 3D reconstruction based on subtraction of these two images and the relative dose measurements were made using in-house software.

Results: Comparing measured radial dose rates with previous results revealed smaller percent errors when PRESAGE™ irradiations were at lower maximum dose. The dosimeters showed small deviations in radial dose function, gp(r), from previous studies. Among the dosimeters irradiated at 1517.3 cGy, the gp(r) compared to previous studies fluctuated from 0.0043 to 0.3922. This suggests small fluctuations can drastically change radial dose calculations.

Conclusion:The subtraction of pre-irradiation and post-irradiation scans of PRESAGE™ dosimeters using an optical-CT scanner shows promising results in determining 3D dosimetry for Xoft Axxent devices; however, further research is recommended.

Funding Support, Disclosures, and Conflict of Interest: NIH Grant#: 5-U24-CA081647-13 ROI Grant#: 5R01CA100835

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