Room: AAPM ePoster Library
Purpose: provide a comparison of air kerma and modified TG43 parameters for the older S7500 Xoft Axxent source cooled with water and the newer S7600 source cooled with Galden™ and determine the impact on final dose rate calculation from these sources.
Methods: Simulations were run using the EGSnrc user code egs_chamber for air kerma rate, dose rate conversion coefficient, radial dose function, and 2D anisotropy for both source models. Simulations were benchmarked to measurement data using the Attix free air chamber and phantoms manufactured in-house at the UWMRRC.
Results: simulated air kerma for the S7600 source was approximately 15% less than that of the S7500 source. The values for radial dose function for the S7600 source were, on average, 4% greater than those of the S7500 source. Additionally, the dose rate conversion coefficient for the S7600 source was 20% greater than the S7500 source. Values for the 2D anisotropy function were on average 3%, 1.7%, and 2% for distances of 1 cm, 2 cm, and 5 cm, respectively. These differences in source construction result in an increase of approximately 3% in dose rate at 1 cm and 90° from the source when compared to the S7500.
Conclusion: This work emphasizes the need for the implementation of new dosimetry parameters for the new S7600 source model, as the introduction of a higher density coolant and minor changes to source construction cause filtration of source output. The use of incorrect parameters for this new source model will result in inaccurate dose calculation and can cause underdosing of patients if used clinically.
Funding Support, Disclosures, and Conflict of Interest: This work was funded in part by Xoft, a subsidiary of iCad, Inc.