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SU-G-TeP2-02: Characterization of An Improved X-Ray Source for Use with the Xoft Surface Applicator.

PURPOSE
To measure the depth dose distribution and half value layers of an updated x-ray source using the Xoft Axxent Surface Applicator.


METHODS
Modifications were made to the existing Axxent HDR X-ray source to increase the dose rate and improve the source life time. Measurements were made comparing dose distributions of this improved x-ray source and the existing Axxent HDR X-ray source. All sources were spatially characterized in a water tank prior to testing and each source passed all acceptance testing prior to measurement. Depth dose measurements were made using nine x-ray sources of each type through a 10 mm Surface Applicator using an ionization chamber at depths of 2, 5, and 10 mm in a Gammex Solid Water phantom, corrected for the ionization chamber collecting volume centroid and the use of a water-like phantom. Half value layers (HVLs) were measured for the family of surface applicators using five improved design sources.


RESULTS
The average normalized surface dose rate for the updated x-ray source is 1.65 Gy/min, in agreement with the existing x-ray source to within 2%. The average normalized dose rate at the other measured depths agrees to within 1%, with dose rates of 1.31 Gy/min, 0.90 Gy/min, and 0.52 Gy/min at 2 mm, 5 mm, and 10 mm respectively. First and second HVLs agree between the two x-ray source types to within standard errors for all Surface Applicators. First HVLs range from 1.45 to 1.58 mm Al and second HVLs range from 2.20 to 2.52 mm Al.


CONCLUSION
Depth dose distributions were measured for the existing Axxent X-ray source and an updated source through the Surface Applicator and shown to be equivalent. Half value layers for the new x-ray source are in agreement with those for the existing source. Funding provided by Xoft, a subsidiary of iCAD.