Fig 1.
Location of the treatment couch with respect to the phantom that is placed on the treatment couch with the ionization chamber point of measurement at the isocenter.
Fig 2.
Panels A, B, C, and D present CBCT images of the phantom placed at the reference position (hanging in front of the treatment couch), extension plate, joint part, and main couch, respectively.
Fig 3.
Pretreatment gamma pass rate calculation diagram constructed using Edose software.
Fig 4.
Panels A and B show the calculation diagram of the TPS dose before and after adding the treatment couch.
Table 1.
Measurements calculated with the presence of a real couch, TPS calculation of actual couch based on CBCT images, and TPS calculation introducing a virtual couch model and corresponding P-values per group.
Fig 5.
Attenuation factors δ changing with gantry angles under different conditions (M1: Extension; M2: Joint; M3: Couch; CBCT1: Extension; CBCT2: Joint; CBCT3: Couch; CT: Couch).
Fig 6.
A: Measured dose values for the different attenuation cases. B, C, and D: Measured (M) and calculated values (CBCT, CT) for the extension, joint, and couch positions, respectively.
Table 2.
Passing rates of the NPC IMRT plan beams after passing through the extension plate, joint, and main couch plate.