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Determination and Evaluation of a Dose-Rate Conversion Coefficient for the Xoft Axxent® Electronic Brachytherapy Source in the Xoft Titanium Cervical Applicator

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S Simiele

S Simiele*, J Micka , W Culberson , L DeWerd , University of Wisconsin, Madison, WI


TH-AB-BRA-7 (Thursday, July 16, 2015) 7:30 AM - 9:30 AM Room: Ballroom A

Purpose: A new NIST-traceable air-kerma standard has been established for electronic brachytherapy (EBT) sources which has motivated the development of a modified AAPM TG-43 dosimetry formalism. Due to the low-energy nature of EBT, it is important to verify that a single dose-rate conversion coefficient (DRCC) value is appropriate for use with each applicator type, as small changes in applicator thickness between individual applicators due to manufacturing tolerances may have a large impact on the DRCC. This work aims to determine the DRCC for the Xoft source in multiple titanium cervical applicators and verify that a single representative DRCC value is acceptable for clinical use.

Methods: The DRCC and radial dose function (RDF) were measured using three titanium cervical applicators and one source. An annulus of Virtual WaterTM was used to position TLD-100 microcubes at 30-degree increments around the source and at radial distances of 1, 2, 3, and 4 cm from the source in a liquid water phantom. A slit collimator, designed to fit inside an HDR1000 Plus well-ionization chamber, was used to measure the anode-output profile (AOP) of each source. The measured profile was used with an MCNP5-simulated AOP to align the manufacturer-stated anode origin in the plane of the microcubes. A statistical analysis was performed to compare the DRCC values measured in each applicator.

Results: Statistical analysis results indicated that there is no significant difference between the DRCCs measured in the different applicators. The RDF values determined in the separate applicators are within 5% of each other at 4 cm depth.

Conclusion: The DRCC was measured in three separate applicators to determine if the difference in applicator thickness would require a DRCC specific to each applicator. The results demonstrate that a single representative DRCC, determined with a subset of titanium cervical applicators, is acceptable.

Funding Support, Disclosures, and Conflict of Interest: This work was partially supported by the NIH radiological sciences training grant T32-CA009206 and Xoft Inc. (a subsidiary of iCAD).

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