Author: Ivan M. Buzurovic, Matthew W. Jacobson, Marjan Khosravi 👨🔬
Affiliation: Brigham and Women's Hospital, Harvard Medial School, Dana-Farber Cancer Institute, Department of Radiation Oncology, University of Massachusetts Lowell, Department of Physics, Lowell, MA/Brigham and Women's Hospital, Harvard Medial School, Dana-Farber Cancer Institute, Department of Radiation Oncology 🌍
Purpose: Annual quality assurance (QA) of high dose rate (HDR) brachytherapy (BT) gynecological (GYN) applicators is critical to ensure accurate and consistent source position and dose delivery. In this study, we developed an automated quantitative method to calculate source position. This method is applied to the annual QA of HDR BT GYN applicators, using CT-film images and auto-registration.
Methods: A sample of 17 Geneva and Utrecht applicator sets (Elekta) were selected for this study. A source distance position was obtained for each applicator set using autoradiography and CT imaging. In the autoradiography approach, the EBT-3 film was irradiated with applicators affixed securely to the film sheet. Four disposable X-SPOT skin markers (Beekley Medical) were placed at each film corner to provide image registration landmarks. CT images were acquired with a radiopaque CT marker inserted inside the applicators. The CT and scanned film images were automatically registered using a four-point registration algorithm developed in MATLAB. The automated quantitative analysis was performed for each applicator to calculate the distance between the center of the corresponding CT marker points and the irradiated surfaces on the film. The distances were computed in 2D using a pixel-based approach and converted to actual distances in millimeters.
Results: The source position analysis for all 17 applicators resulted in an average distance of 0.42±0.01 mm. The average source displacement for Geneva applicators was 0.28±0.01 mm, with a maximum of 0.69±0.01 mm and a minimum of 0.02 ±0.01 mm. For Utrecht applicators, the average displacement was 0.56±0.01 mm, with a maximum of 0.94±0.01 mm and a minimum of 0.22±0.01 mm.
Conclusion: The proposed method automatically registers and calculates the source displacement. This study shows the feasibility of the technique for implementation in clinical setups, with results recorded in submillimeter accuracy. Future work includes additional experiments for various applicator types.