Development of a 3D dose distribution validation water tank for rotating Gantry treatment terminals

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 horizontal, vertical and 45° beamline. And those water tanks are inefficient, which cannot meet the multi-angle dose validation requirements of the advanced rotary Gantry beamline treatment rooms. This study aims to meet the beam detection requirements of multi-directional irradiation of Gantry beamline, a 3D water tank for multi-angle beam dose verification was developed. [Methods] The water tank box was made of Polymethyl Methacrylate (PMMA) material, which could be rotated around the isocenter under the drive of the motor. The structure of the water tank was simulated by using Solidworks Simulation software package, 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, and a 3D dose distribution of the pencil beam can be obtained. The measured results were compared with those of a PTW water tank. [Results] According to the test results, the maximum position error of the probe is 0.132mm when the probe is moving in the depth direction, the maximum position error of the probe is 0.24mm in the Y and Z directions for the probe position adjustment, and the dose measurement deviation is 0.5%±1.18%. [Conclusions] By measuring the lateral profile dose distribution of the beam at different depths in the water, the water tank can quickly and accurately provide the 3D dose distribution of a pencil beam. This device can provide basic data for treatment planning systems and improve the efficiency of regular quality assurance practice. At the same time, with high precision of the 3D motion mechanism, the structure of the water tank is reliable, and the whole measuring device can be rotated around the isocenter of the treatment head. Therefore, this device can meet the beam detection requirements of multi-directional irradiation in the Gantry treatment rooms.