Author: Daming LI, Jinsen Xie, Zhe Zhang 👨🔬
Affiliation: Peking University Shenzhen Hospital Radiotherapy Department, School of Nuclear Science and Technology, University of South China 🌍
Purpose:
This study aims to investigate the feasibility of online dose measurement of the Trilogy linear accelerator output based on target current pulse signals.
Methods:
A data acquisition board was adopted to collect the target current pulse signals of the Trilogy accelerator. The feasibility of using pulse number (PNO.) as a dose metric was first evaluated. Subsequently, the VMAT control point information was converted into a time-dose curve and used as a reference. The measured pulse dose data were transformed similarly, and the mean square error (MSE) method was applied to compare the similarity between the two curves. For abnormal dose output monitoring, pulse output data from DMLC fields with MU values of 2, 5, 10, 20, 50, and 100 for a 10×10 cm² field were collected. EPID was used to acquire dose images, and the gamma passing rate and beam-on duty cycle were calculated.
Results: The PNO. was only related to MU, with no dependence on gantry angle or dose rate. The variation of PNO. remained within 0.5% under 100 MU conditions, and the repeatability test results were consistent. In linear tests from 1 to 500 MU, MU and pulse count showed a strong linear correlation, which was further verified in VMAT fields, with a correlation coefficient (R²) exceeding 0.99. In the VMAT field test, the average MSE was 3.34E-05 (range: 9.39E-07 to 1.31E-04). In the abnormal execution test, the passing rate under the 2% 2mm gamma protocol increased with MU: 7.9%, 19.5%, 29.9%, 83.4%, 93.5%, and 95.3%, respectively. The duty cycle increased from 7.69% at 2 MU to 99.88% at 100 MU.
Conclusion: The target current pulse count is strongly linearly correlated with MU, and establishing a time-dose relationship can effectively enable online measurement of the Trilogy accelerator's output dose.