This study aimed to evaluate changes in the deformation of the entrance window on a phantom for a horizontal beam geometry with a window thickness of 5 mm. The window deformation over time was measured using a dial indicator for 12 h after water filling. The window deformation was in the range of 0.17-0.37 mm among the three phantoms. The change in deformation over time was found to be 0.06 mm or less 12 h after filling the phantom. For off-center measurements, the maximum difference in variation among the five points in each of the three phantoms was 0.12, 0.11, and 0.07 mm. The window deformation on the phantom for a horizontal beam geometry with the window thickness of 5 mm was considered almost negligible when appropriately used. However, it is important to control the quality of the phantom according to the usage conditions.
Keywords: Entrance window; Horizontal beam; Water phantom; Window deformation.
© 2021. Japanese Society of Radiological Technology and Japan Society of Medical Physics.