Author: Sen Bai, Guyu Dai, Dong Gao, Lecheng Jia, Guangjun Li, Yanfang Liu, Ying Song, Qing Xiao, Wei Zhang 👨🔬
Affiliation: United Imaging Healthcare, West China Hospital of Sichuan University, Shenzhen United Imaging Research Institute of Innovative Medical Equipment 🌍
Purpose:
Electronic portal imaging device (EPID) is currently the most widely used in-vivo dosimetry (IVD) device. However, the effective detector area shortage hinders further applications. This study aims to evaluate the characteristics of a novel EPID system with the size of 65 cm × 61 cm equipped in the newly released Halos Tx CT-linac.
Methods:
Basic physical characteristics, including short-term repeatability, dose-response linearity, dose-rate dependencies, and the influence of gantry angle on dose, were first tested. Next, 1687 treatment beams from West China Hospital were randomly selected to test the applicability for different treatment sites of the EPID from Halos Tx and other EPIDs. Then, the sensitivity of the EPID in detecting machine-related errors, including jaw position, MLC leaf position, output, and collimator rotation errors were evaluated. Additionally, a typical breast cancer patient set-up error test was simulated using a female thorax phantom, and the error sensitivity was investigated.
Results:
The EPID showed high stability of short-term repeatability, dose-response linearity, dose-rate, and gantry angle, with maximum deviations determined to be 0.25 %, 0.6 %, 0.4 %, and 0.7 %, respectively. Benefitting from the large effective detector area, this EPID successfully monitored all planning beam fields from various treatment plans while conventional EPID systems could merely monitor 60 % beam fields of breast cancer patients. The machine-related error sensitivity of the EPID was 0.2 mm for jaw position, 0.2 mm for MLC position, 0.1 % for output, and 0.5° for collimator rotation, respectively. The EPID successfully monitored the breast cancer patient set-up errors in vivo during the process of beam delivery and showed high sensitivity, especially for the beam of 56°~140°.
Conclusion:
Our preliminary results demonstrate that this new EPID possesses superior stability, broad applicability, and high sensitivity and shows the potential to enable novel applications for EPID-based QA for radiotherapy.