SU-G-201-10: Experimental Determination of Modified TG-43 Dosimetry Parameters for the Xoft Axxent® Electronic Brachytherapy Source

Abstract

Purpose: The establishment of an air kerma rate standard at NIST for the Xoft Axxent® electronic brachytherapy source (Axxent® source) motivated the establishment of a modified TG‐43 dosimetry formalism. This work measures the modified dosimetry parameters for the Axxent® source in the absence of a treatment applicator for implementation in Xoft's treatment planning system. Methods: The dose‐rate conversion coefficient (DRCC), radial dose function (RDF) values, and polar anisotropy (PA) were measured using TLD‐100 microcubes with NIST‐calibrated sources. The DRCC and RDF measurements were performed in liquid water using an annulus of Virtual Water™ designed to align the TLDs at the height of the anode at fixed radii from the source. The PA was measured at several distances from the source in a PMMA phantom. MCNP‐determined absorbed dose energy dependence correction factors were used to convert from dose to TLD to dose to liquid water for the DRCC, RDF, and PA measurements. The intrinsic energy dependence correction factor from the work of Pike was used. The AKR was determined using a NIST‐calibrated HDR1000 Plus well‐type ionization chamber. Results: The DRCC was determined to be 8.6 (cGy/hr)/(µGy/min). The radial dose values were determined to be 1.00 (1cm), 0.60 (2cm), 0.42 (3cm), and 0.32 (4cm), with agreement ranging from (5.7% to 10.9%) from the work of Hiatt et al. 2015 and agreement from (2.8% to 6.8%) with internal MCNP simulations. Conclusion: This work presents a complete dataset of modified TG‐43 dosimetry parameters for the Axxent® source in the absence of an applicator. Prior to this study a DRCC had not been measured for the Axxent® source. This data will be used for calculating dose distributions for patients receiving treatment with the Axxent® source in Xoft's breast balloon and vaginal applicators, and for intraoperative radiotherapy. Sources and partial funding for this work were provided by Xoft Inc. (a subsidiary of iCAD). This work was also supported by the Radiological Sciences T32 Training Grant through the University of Wisconsin‐Madison Medical Physics department (5T32CA009206‐37).

Biological Characterization of the Effects of Filtration on the Xoft Axxent® Electronic Brachytherapy Source for Cervical Cancer Applications

“…These gradients are indicative of the dose distribution to be delivered to the cells for the BS and SIA. Further, these dose distributions are consistent with the works of Walter et al ( 37 ) and Simiele ( 38 ) which investigated the dosimetric properties of these sources following a modified TG43 approach.…”

Calculated and measured radiation dose for the low energy xoft axxent eBT X-ray source

“…The source model S700 consists of a miniature (length = 10 mm, diameter = 2 mm) x-ray tube whose welding properties are characterized according to the American Association of Physicist in Medicine (AAPM) Task Group 43 (TG-43) [14][15][16]. Since the source has an operating voltage of 50 kV, there is no need for shielding as in the HDR brachytherapy system where Ir192 source is used [17,18]. In addition, the system can produce air kerma up to 1400 Gy.cm 2 .h − 1 with a tube current of 300 µA at an operating voltage of 50 kVp, which is approximately three times larger than the value produced by the Ir192 source used in the HDR system [19][20][21].…”