Program Information
Investigation of a Source Model for Use with a New Electronic Brachytherapy Tandem by Film Measurement
E Martin*, K Sowards , B Wang , Univ Louisville, Louisville, KY
Presentations
PO-BPC-Exhibit Hall-17 (Saturday, March 18, 2017) Room: Exhibit Hall
Purpose: To investigate the accuracy of a vendor-supplied 12mm source model for a new Xoft Axxent 0-degree titanium tandem at varying distances by film measurement.
Methods: We measured the 2-dimensional dose distribution at varying distances from the tandem location in water using radiochromic film (Gafchromic EBT3). A 0-degree tandem was placed vertically in a water phantom. An array of radiochromic film was then positioned parallel to the tandem. The film measurements were taken at a distance of 1, 2, 3, 4, and 5 cm from the tandem. Both measured and calculated dose distributions were normalized to their respective maximum pixel values. Cross (x) and longitudinal (y) profiles were obtained at the resulting maximum pixel value location. Full Width at Half Maximum (FWHM) values of the x and y profiles were then analyzed using Microsoft Excel, and percent differences of the FWHM were compared between measured and calculated.
Results: Three iterations, using three different film holding techniques, was employed and all iterations showed that as the distance from the tandem increased, the FWHM value agreed better with the treatment planning. At 1cm distance from the tandem, the FWHM percent difference was the largest at 51.01% in the x profile, while it decreased to 2.88% in the y profile at the distance of 5cm. The large percent difference closer to tandem could be a combination of several factors such as measurement uncertainties, incorrect treatment planning factors, or manufacturing errors in the tandem/source. Further work is under way to analyze these individual factors and to propose correction factors.
Conclusion: We quantified the agreement between the measured and planned dose distributions for a new Xoft Axxent 0-degree titanium tandem at varying distances in this study. Our preliminary results showed that as the distance is increased from the tandem, the agreement improves.
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