Purpose: 3D water tanks are utilized to acquire data as part of the annual quality assurance on linear accelerators. A 1D water tank alone or in combination with a modern array detector may offer an attractive alternative in terms of cost and expeditious results. In this work, we compared aspects of our annual QA acquired with and without the use of a 3D water tank.
Methods: The 3D water tank used was Standard Imaging’s DoseView 3D and the alternate equipment was Sun Nuclear’s 1D Scanner as well as the Ion Chamber (IC) profiler. With the IC profiler’s inherent depth of 0.9cm, additional water slabs were used as needed to acquire profiles for photons (6MV, 6FFF, 10MV, 10FFF, 15MV), and electron energies (6e, 9e, 12e, 15e, 18e) for different field sizes and different depths. Furthermore, by irradiating the 1D tank from the side, that is a gantry of 90 (or 270) with the tank atop the couch at 100cm SSD to the side, we also acquired profiles using the 1D tank alone. These results were compared with those acquired using the 3D water tank.
Results: We observed excellent agreement between the 3D tank versus the IC profiler with a measured discrepancy within 1% for all photons/electrons profile flatness and symmetry and within 2% for all electron flatness. The calculated Beam Profile Constancy for the 6MV, 10MV and 15MV beams between the 3D and 1D water tank were excellent, observing 0.49%, 0.44% and 0.79% respectively for the 10x10cm field and correspondingly 0.38%, 0.54% and 0.62% for the 20x20cm field.
Conclusion: A 1D scanner and a detector array produce comparable profile results vis-a-vis a 3D scanner and therefore offer an attractive alternative. The limitation is with the maximum field size attainable as well as the range of depths achievable using a 1D scanner.