In order to ensure the accuracy of the dose received by the patient in radiotherapy, it is usually necessary to verify the plan before treatment, and the water tank is widely used to achieve this purpose. However, the existing dose validation tanks can only be used for beam therapy terminals with horizontal, vertical and 45° angles, which cannot meet the multi-angle dose validation requirements of the advanced rotary Gantry beamline treatment rooms.

This study aims to develop a three-dimensional (3D) water tank for multi-angle beam dose verification, so as to meet the beam detection requirements of multi-direction beam irradiation of gantry beam line.

The water tank box was constructed from Polymethyl Methacrylate (PMMA) and driven by the motor to rotate around the isocenter. Solidworks Simulation software package was employed to simulate the structure of the water tank, and the motion accuracy of the 3D motion mechanism was evaluated. The lateral profile dose distribution of the beam at different depths in the water was measured by a multi-strip ionization chamber (MSIC), and a 3D dose distribution of the pencil beam was obtained by stacking the profile dose distribution measured at different depths. The measurement results were compared with data obtained from commercial PTW water tank.

Evaluation results show that, the maximum position error of the probe is 0.132 mm when the probe is moving in the depth direction, the maximum position error of the probe is 0.24 mm in the Y and Z directions for the probe position adjustment, and the dose measurement deviation is 0.5%±1.18%.

The water tank proposed in this study can quickly and accurately provide the 3D dose distribution of a pencil beam, hence, provide basic data for treatment planning systems and improve the efficiency of regular quality assurance practice. The whole measuring device can be rotated around the isocenter of the treatment head, meeting the beam detection requirements of multi-directional irradiation in the Gantry treatment rooms.