Author: Shixiong Huang, Daming Li 👨🔬
Affiliation: The Affiliated Nanhua Hospital, University of South China, The Affiliated Cancer Hospital of Xiangya School of Medicine, Central South University/Hunan Cancer Hospital 🌍
Purpose: To assess the feasibility of using target current pulse signals to evaluate the output dose of medical standing wave electronic linear accelerators.
Methods: The Target I signal of the accelerator was collected using an Altec data acquisition card. Pulse count repeatability at the same monitor unit (MU) for 100 MU was analyzed, along with the effects of gantry angle and dose rate on pulse count. The correlation between MU and pulse count was studied for 136 volumetric modulated radiation therapy (VMAT) fields. The similarity between theoretical and measured gantry-dose curves was evaluated using the mean square error (MSE) method. Pulse output was also measured for fixed fields under 10×10 cm² dynamic multi-leave collimator (DMLC) wedge fields with MU values of 2, 10, and 100. In VMAT tests, pulse signals were measured with gantry variations, considering both maximum and control point-defined gantry speeds.
Results: Pulse count, gantry angle, and dose rate variations for 100 MU were within 1%. A strong linear correlation (R² = 0.999) was observed between MU and pulse count in both linear and VMAT tests. For constant gantry angles, the theoretical and measured gantry-dose curves were similar, with an average MSE of 2.49E-06. In abnormal execution tests, vacant ratios for wedge fields were 8.07%, 67.16%, and 100% at 2, 10, and 100 MU, respectively, with pass rates of 7.9%, 29.9%, and 95.3%. The MSE improved from 3.50E-05 to 8.01E-06 when adjusting gantry speed.
Conclusion: The target current pulse method can effectively measure the output dose of both fixed and VMAT fields in medical standing wave electronic linear accelerators.