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Comparison of An Improved X-Ray Source for Use in All Applications with the Existing Xoft X-Ray Source

L Kelley*, T Rusch, R Neimeyer, Xoft, Inc., San Jose, CA

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose:
To compare the dose delivered to target tissue between the Xoft X-ray source and an improved X-ray source for use in Xoft applicators using existing TG-43 parameters for the X-ray source dose distributions.

Methods:
Modifications were made to the existing Axxent HDR X-ray source to increase the dose rate and improve the source lifetime. Measurements were made comparing the dose through balloon applicators, vaginal cylinders, and the cervical applicator to the prescription surface/point. Isodose contours for the balloon and vaginal applicators were also compared. In all cases, the same treatment plan was used for each X-ray source type for a given applicator. Measurements were made in a shielded water tank using Gammex Solid Water™ phantoms. The test fixture held Gafchromic™ EBT3 film and an encapsulated PTW 34013 ionization chamber mounted at the prescription surface 90° from the applicator plane. Measurements from three of each type X-ray source were averaged.

Results:
Balloon IORT treatment plans were evaluated for volumes of 20cc to 130cc. Dose differences ranged from -5.1% for the minimum fill to -0.3% for the largest fill. For the Balloon applicator, the average measured dose difference at the 1 cm APBI prescription surface ranged from -3.0% for a 3.4 cm diameter balloon to -0.2% for a 5.4 cm diameter balloon. For vaginal applicators, the average dose difference at the 0.5 cm prescription surface ranged from -4.4% for the 30 mm applicator to -1.8% for the 35 mm applicator. For the cervical applicator, the average dose difference at point A was -2.8%.

Conclusion:
When using the improved X-ray source, the difference between dose delivered to the prescription surface for all applicators tested was less than 6% with no modification of the TG-43 parameters. It is expected that an update to these parameters for the new source will improve the agreement

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Funding Support, Disclosures, and Conflict of Interest: Funding provided by Xoft, Inc.

Keywords

Not Applicable / None Entered.

Taxonomy

Not Applicable / None Entered.

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