Room: AAPM ePoster Library
Purpose: We compared the positional accuracy of the jaw and multi-leaf collimator (MLC) in the Elekta Synergy with Agility head using a high sampling rate log file (HLF).
Methods: A Dynamic Jaw (DJAW) plan was created in which the Y jaw that maintained the 10 mm gap moved from the Y1 side to the Y2 side between the two control points (CP) and then returned to the starting position. The plan changed the moving speed in seven steps (5, 10, 15, 20, 25, 30, 35 mm/sec), and further changed the gantry angle and the collimator angle in three steps (Ga0°/Co0°, Ga90°/Co90°, Ga270°/Co90°). The HLF was acquired at the same time as the beam irradiation. Next, a similar DMLC plan was created in the MLC and an HLF was acquired. Each acquired log file was imported into our software, and the maximum error, mean absolute error (MAE) and root mean square error (RMSE) of the Y jaw and MLC were compared. In addition, the plotting positions of the jaw and MLC recorded in the HLF for each sampling time and the theoretical jaw and MLC positions between CPs were visualized and compared.
Results: The maximum error in the jaw was 3.3 mm at a gantry angle of 270° at 35 mm/sec, and the maximum error in the MLC was 4.2 mm when the gantry angle was 0°. The MAE and RMSE did not exceed 1.0 mm under any conditions. In addition, it was confirmed that the plotting position overshot the returning CP in the MLC, while the jaw could not reach the CP and started to return.
Conclusion: Using an HLF to visualize and analyze the positional error during irradiation, enabled us to confirm the difference in behavior between the jaw and the MLC.