Fig. 1. Schematic of 3D water phantom measurement program

Fig. 2. Overall structural diagram of the 3D water tank

Fig. 3. Solidworks simulation results of box tank structure by Solidworks (a) Deformation of open box tank, (b) 8 N·m preload on tank top cover, (c) Deformation of the sealed tank, (d) Deformation of tank placed at 45° angle position

Fig. 4. Diagram of sealed water phantom model

Fig. 5. Diagram of multi-strip ionization chamber and flexible circuit boards

Fig. 6. Schematic of three-dimensional movement mechanism

Fig. 7. Collimation calibration of the 3D moving mechanisms (a) Collimation calibration platform of 3D moving mechanisms, (b) Position deviation during X-direction movement, (c) Position deviation during Y-direction movement, (d) Position deviation during Z-direction movement

Fig. 8. Illustration of sealing performance test of water phantom

Fig. 9. Snapshot of water phantom beam test at treatment room

Fig. 10. 3D dose distribution of the 400 MeV·u^-1 carbon ion pencil beam in water (a) Measured results with the water tank, (b) Simulation results of Geant4

Fig. 11. Comparison of the depth dose curves measured by the 3D water phantom with the results measured by the PTW MP3 water phantom (a) and relative deviation (b)