Room: Exhibit Hall
Purpose: To develop an efficient method to verify HDR Ir-192 source dwell positions inside of various HDR applicators using fluoroscopic images. This method provides quantitatively accurate measurements, and obviates the need for radiographic film which is commonly used in applicator QA.
Methods: Fluoroscopic images of different gynecological applicators with HDR Ir-192 source (GammaMed+, Varian, CA) were acquired using a C-Arm unit (GE 9800). Source dwell positions inside of tandem/ovoids, interstitial tandem/ring, cylinder applicators (Varian, CA) and M.A.C interstitial applicators (Eckert&Ziegler BEBIG, NY) were investigated using these images. Different imaging techniques were developed depending on applicator construction material. The distal end of the source wire was verified relative to the tips of the applicators to comply with AAPM TG-56 guidelines of commissioning and periodic QA. All images were acquired with 1cm interval x-ray markers which provide a distance reference to determine the distal source dwell positions in the images. The digital image analyses were performed using the open source software ImageJ.
Results: Source wire trajectory and dwell positions inside all plastic and titanium applicators except for those made of steel (Miami-style applicator) were visualized in fluoroscopic images. The distances between the 1st dwell positions and the tips of applicators were measured within 1.5mm (2.0mm for interstitial rings). Optimal X-ray imaging techniques for plastic and titanium applicators were 45 kVp (1.0mAs) and 65 kVp (0.3mAs) for the active source to be visible inside the applicators. Our institution established this method as periodic QA for existing applicators and for commissioning of new applicators.
Conclusion: Real-time fluoroscopic imaging of HDR applicators simplifies the applicator QA on source dwell position coincidence. Fluoroscopic imaging of both actual source and applicator enables direct verification of source dwell positions within the applicator instead of going through cumbersome multi-step process when radiographic films are used for QA.