Room: AAPM ePoster Library
Purpose: Two-dimensional arrays of ion chambers have become useful for acceptance testing, commissioning, and patient-specific QA. Due to the finite range of light ion beams, it is often desirable to make measurements at multiple depths for a single portal. Exchanging slabs of solid phantoms is an inefficient use of physicist and treatment room time. A water phantom capable of scanning a large array through different depths is desirable.
Methods: A new phantom was designed and built to scan both a PTW XDR 2-D array and a large diameter parallel plate ionization chamber (LDIC) through water.
Results: The inside water volume is 375 mm x 370 mm x 430 mm and supports a horizontal beam direction. The depth of the detector can be commanded remotely with a resolution of 0.01 mm, a reproducibility of ± 0.2 mm, and an accuracy of ± 0.5 mm. The phantom surface-to-isocenter distance can be remotely adjusted through a range of 200 mm. Due to the depth of the chambers in the XDR detector, the thickness of the front phantom window, thickness of the front wall of the water proof detector container, and the closest approach of the container to the front wall, the minimum measurement depth is 24 mm.
Conclusion: A new phantom has been built that provides efficient changes of depth and surface distance allowing matching of plan and measurement scatter conditions. Although designed for use with light ion beams, it may be useful for other radiation beams as well.