Room: AAPM ePoster Library
Purpose: We present a QA methodology that includes a quantitative analysis of the ¹?²Ir HDR source first dwell position within the applicator structure and its coincidence with the x-ray marker.
Methods: Sixty-four different applicator sets with corresponding x-ray markers were tested including the Venezia, Utrecht, Fletcher, cylinder, multichannel cylinder, tandem and ring sets. Each set of applicators was fixed to a 5" by 8" piece of EBT3, XRQA2 or RTQA2 radiochromic films. The x-ray markers were inserted into the applicators and imaged using both x-rays and HDR source post markers removal. Four ball bearings (BBs) and ink-dots were placed at each corner of the film prior to imaging to allow for accurate quantitative analysis. The film was scanned and the image was registered to the x-ray image based on an affine four-points registration. An in-house developed algorithm was utilized for automatic position assessment of the coordinates of the source and x-ray markers using centroid analysis of iso-pixel values.
Results: Source position accuracy for all applicators was found to be (0.10 ± 0.39) mm in the direction of source trajectory. The algorithm was able to detect and quantify the lateral displacement of the source with respect to the x-ray marker position; this was not the case with a standard qualitative QA technique. Optimum Ci·sec nomograms were generated for each film model to obtain adequate exposure and maximum accuracy of the position detection (0.01 mm). XRQA2 film showed minimum fiducial registration error since the BB shadow on the film could be used for registration instead of the ink-marks. Fiducial localization error was the lowest in this case.
Conclusion: The proposed method is capable of quick and quantitative analysis of the HDR source first dwell position. The method was used to improve the current QA of gynecological brachytherapy applicators.
Funding Support, Disclosures, and Conflict of Interest: The authors have no conflicts to disclose. This work was supported partially by the Natural Sciences and Engineering Research Council of Canada Grant No. 386009 and No. 432290. S.A. is a Ph.D. Candidate supported by the scholarship program at King Faisal Specialist Hospital & Research Centre.