HDR Brachytherapy Imaging Quality Assurance: Ensuring Accuracy and Safety In Dose Delivery
Abstract
Purpose
Routine imaging QA is critical for ensuring precise HDR prostate brachytherapy delivery. This study sought to verify the accuracy of the ultrasound imaging system and to identify potential improvements in quality-control processes and real-time treatment monitoring.
Methods
Initial QA testing was performed using the CIRS Model 053S prostate phantom, with volume reconstruction performed on the Varian Vitesse ultrasound-guided brachytherapy planning system. Reconstructed target and OAR volumes were compared to the known phantom volume. During probe manipulation, an image discontinuity was found at the probe zeroing location. To characterize this discontinuity, the stepper probe was rotated at fast, medium, and slow speeds with the zero-point positioned at mid-gland, and the resulting discontinuity measured. A retrospective comparative analysis on patient imaging was conducted between pre-treatment MRI and day-of-treatment transrectal ultrasound (TRUS) prostate volumes, with data retrieved from patient databases. Only cases from 2024-2025 in which imaging was performed within a three-week interval were included.
Results
QA results confirmed system accuracy within the 5% error threshold recommended by AAPM Task Group 128. Patients were grouped by treating physician into three cohorts (n=14, 24, and 15). The mean percent volume changes between MRI and TRUS were +24.6%, +0.5%, and -0.4% for the three physicians, respectively, suggesting substantial inter-physician variation in prostate volume assessment. Regarding image discontinuity evaluation, faster probe rotation produced larger discontinuities, with measured gaps of 3.4 mm (fast), 2.3 mm (medium), and 1.8 mm (slow). Placing the zero-point before or after the prostate led to no discontinuity, and slower turns produced a notably smaller discontinuity.
Conclusion
These findings suggest a notable physician-dependent influence on prostate contouring with the same image quality that may impact treatment planning and dose-delivery accuracy in brachytherapy. Further investigation is warranted to identify sources of discrepancies and reduce inter-physician variability, ensuring consistent and precise patient outcomes.