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Quality Assurance Tool for Determination of Position and Transit Time of a Co-60 Source in High Dose Rate Brachytherapy

G Piriz1, H Ortega2, G Gonzalez-Sprinberg2*, (1) Faculty of Medicine, Universidad de la Republica, Montevideo, UY, (2) Faculty of Sciences, Universidad de la Republica, Montevideo, UY

Presentations

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

Room: AAPM ePoster Library

Purpose: In high dose rate (HDR) remote afterloading brachytherapy, quality assurance (QA) strongly depends on the accurate determination of the strength of the source, the dwell time, and also its position and transit time. In order to check the position and transit time in a remote afterloader with a Co-60 source, two devices were designed, constructed and characterized in this work. Such devices were designed focusing on accuracy, low cost, and short time involved in the periodic controls.


Methods: Two holders were constructed, one of tungsten and the other one of Cerrobend, based on a standard PMMA calibration insert of a well chamber. PMMA windows of different thickness were tested for the holders. In order to optimize the signal, the window width and several characteristic points of the response curve were determined for each holder. From these measurements, it was possible to determine the precision of both dwell positions and transit time.



Results: In the case of Cerrobend, a sensitivity of the source position better than 2%/mm and a maximum precision of 0.15 mm were obtained, whereas a sensitivity and maximum precision of 3%/mm and 0.09 mm, respectively, were obtained for tungsten. On the other hand, the transit time was determined with both devices with a relative precision of 8.8% and 51% for Cerrobend and tungsten, respectively.



Conclusion: This work shows the feasibility of these holders for routine quality assurance on the source in accordance with international brachytherapy protocols and standards.

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Keywords

Quality Assurance, HDR, Co-60

Taxonomy

TH- Brachytherapy: Calibration & Quality Assurance

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