Fig 4.

The left‐hand side [Fig. 4(a)] depicts the front side of the filled water phantom inside the magnet located in the isocenter of the research room, equipped with a small area Bragg Peak chamber (type 34073, PTW, Freiburg, Germany). Note the thin‐window Bragg‐peak chamber (type 34080, PTW, Freiburg, Germany) used for reference field measurement at the front of the phantom. The figure on the right‐hand side [Fig. 4(b)] depicts the back side of the water phantom inside the magnet. Note the black stepper motors located outside of the magnetic field. [Color figure can be viewed at wileyonlinelibrary.com]