Room: Exhibit Hall | Forum 6
Purpose: we evaluate a novel real-time imaging and dosimetry solution for HDR brachytherapy source position and plan verification using a portable flat panel detector customized for HDR delivery.
Methods: The radioactive Ir-192 from GammaMed Plus Afterloader was used as the imaging source and a portable FPD from Varex Imaging was used to acquire real-time images during HDR delivery. Solid water slabs of various thickness simulating different body sizes were put between the FPD and the source. A 2-cm PMMA slab with two inserted aluminum bars (3-mm thick) was also used to simulate bone density heterogeneity. Treatment plans of different dwell positions and dwell times were tested. Detector gain calibration was performed by placing the detector far away from the source. A mathematical algorithm was derived to determine source position coordinates relative to origin from FPD images, and these source positions were compared to those from the treatment plan.
Results: The detector signal of central 150x150 pixels from various water thickness can be modeled with an exponential and inversed squared function. With the inverse squared correction only, the source position can be determined within 1% accuracy for the test case of 2-cm PMMA plus 3-cm water slab. For the test of 2-cm PMMA plus 1-cm water slab, the position accuracy increased to 5-10%. However, adding the attenuation correction term into the model improved the accuracy. The overall temporal accuracy of dwell times was less than 4%, which was further improved by increasing the detector acquisition speed.
Conclusion: The phantom tests provide promising results for this novel HDR real-time verification method using FPD. Strategies to improve the algorithm are in development for higher tracking accuracy, and a full clinical workflow simulation can demonstrate the utility of this method for HDR brachytherapy treatment validation and QA.