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
TU-C3-GePD-T-4 (Tuesday, August 1, 2017) 10:30 AM - 11:00 AM Room: Therapy ePoster Lounge
Purpose: To investigate the accuracy of a vendor-supplied source model for a new Xoft Axxent 0-degree titanium tandem by film measurement
Methods: We measured the anisotropy factors at varying distances and angles from the tandem in water using radiochromic film (Gafchromic EBT3). A 0-degree tandem was placed vertically in a water phantom. Four pieces of film, each at varying depths, were positioned orthogonal to the longitudinal axis of the tandem for azimuthal anisotropy measurements. Polar anisotropy measurements were taken with the film aligned parallel to the tandem. An absolute dose calibration for the film was attempted using Air Kerma, and verified with a PTW 34013 Soft X-Ray Chamber. The film measurements were analyzed using different color channels, each with there own film calibration curve, according to published data regarding film’s sensitivity at different dose ranges. The measured polar anisotropy for the 0mm source position was compared to the vendor’s data. Azimuthal anisotropy was measured as a function of the radius and angle, and normalized to the mean value over all angles at the specified radius.
Results: The azimuthal anisotropy of the tandem and source was found to be consistent for different positions along the tandem’s longitudinal axis and at varying distances from the tandem. The custom tandem, which has a thicker tip than the wall, was attenuating the 50 kV photons more than expected, at the angles where the photons had more wall material to traverse. As distance increased, anisotropy values had better agreement.
Conclusion: We quantified the agreement between the measured and provided anisotropy factors for a new Xoft Axxent 0-degree titanium tandem in this study. Radiochromic film response at low kV energy was also explored. Our preliminary results showed that vendor supplied TG-43 values were appropriate and that radiochromic film was an appropriate dosimetric measurement device.
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