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MO‐EE‐A4‐02: Quality Assurance of 4D‐CT for Radiotherapy: Development of a Cantilever Phantom
Author(s) -
Dunn L,
Kron T,
Franich R
Publication year - 2010
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.3469098
Subject(s) - imaging phantom , scanner , amplitude , quality assurance , dosimeter , biomedical engineering , computer science , physics , acoustics , nuclear medicine , optics , medicine , radiation , external quality assessment , pathology
Purpose : Modern 4D‐CT machines require strict QA to ensure the accuracy of motion management protocols. A cantilever motion‐phantom is presented capable of evaluating the accuracy of 4D‐CT over a large range of amplitudes/frequencies. The phantom is light‐weight, easy‐to‐use, portable, and is compatible with any motion signal acquisition software/hardware. Method and Materials : A motion phantom was designed to enable accurate QA of 4D‐CT technology. Design criteria include: large range of motion amplitudes & frequencies, portable, light‐weight, and tissue equivalence within the Field of View. The phantom is capable of producing large variable‐amplitude, variable‐frequency motions via a DC motor and eccentric rotating cam. The amplitude can be varied from 10 – 60 mm / frequency 1 – 40 cycles per minute. A Phillips brilliance big‐bore CT scanner was used to compare static versus moving CT numbers for Water, Nylon, Cork, Perspex and Teflon (−1000 ‐ +800 HU) with fixed amplitude of 55 mm and varied frequency from 2–8 s (2 s intervals). CT numbers per‐phase for static and moving objects were recorded. Results : Results for the analysis of CT numbers across 10 phases of motion show a discrepancy at mid inhale / exhale points between static and moving objects of the same composition. This is in part due to the steeper motion gradients at these phases in contrast to the zero‐gradient phases at peak‐inhale / exhale. Conclusion : A phantom is presented which meets the criteria for modern 4D‐CT QA. Portability makes this phantom an effective multi‐center tool for QA of 4D‐CT for radiotherapy. The phantom is light‐weight, easy to use, has a large range of motion profiles, is able to carry a substantial load due to its cantilever construction and its large motion allows problems to be identified quickly with minimal time required at the scanner.