Development of System for on-site dosimetry audit of High Dose Rate Brachytherapy

Background : Various international institutions established key quality assurance guidelines for radiation therapy, focusing on treatment accuracy and equipment reliability. Despite international standards, the lack of an independent audit system in South Korea has led to quality management challenges in high-dose-rate brachytherapy, prompting this study to develop a precise source activity measurement system and regulatory MATLAB code. Methods : Variations in Remote After-Loading System (RALS) models across institutions are considered, with Standard Imaging source holders and a CDX2000B electrometer used for accurate source strength measurements, focusing on maximum point accuracy. Mechanical accuracy checks involve assessing dwell position accuracy, reproducibility, and offset using self-developed phantoms with in-house MATLAB code, supported by EBT3 film for precise measurement and verification of radiation source positions and offsets. Results : Measured data present the discrepancy between measured and calculated values, with uncertainty observed below 0.14%. Additionally, The developed in-house MATLAB code for film data analysis, utilizes grayscale window analysis for accurate identification of irradiated points, demonstrating minimal position and step size errors, affirming the precision of the method. Conclusion : In this study, we developed an audit system integrating a source strength measurement system and mechanical accuracy check phantoms, utilizing a well-type chamber – electrometer setup and in-house MATLAB code. We achieved audit suitability with appropriate uncertainty, compatible across various Remote After-Loading Systems (RALS). Uncertainty assessments resulted in proposed expanded uncertainties (k = 2) of 2.72% and 2.71% for models 70010 and 72280. Based on these results, we plan to implement this audit system nationwide to comply with domestic regulations.