- Title
- Development and testing of an improved dosimetry system using a backscatter shielded electronic portal imaging device
- Creator
- King, Brian W.; Morf, Daniel; Greer, Peter B.
- Relation
- NHMRC.569211
- Relation
- Medical Physics Vol. 39, Issue 5, p. 2839-2847
- Publisher Link
- http://dx.doi.org/10.1118/1.4709602
- Publisher
- AIP Publishing
- Resource Type
- journal article
- Date
- 2012
- Description
- To investigate the properties of a modified backscatter shielded electronic portal imaging device (BSS-EPID) and to develop a dose model to convert BSS-EPID images to dose in water as part of an improved system for dosimetry using EPIDs. Methods: The effectiveness of the shielding of the BSS-EPID was studied by comparing images measured with the BSS-EPID mounted on the support arm to images measured with the BSS-EPID removed from the support arm. A dose model was developed and optimized to reconstruct dose in water at different depths from measured BSS-EPID images. The accuracy of the dose model was studied using BSS-EPID images of 28 IMRT fields to reconstruct dose in water at depths of 2, 5, 10, and 20 cm and comparing to measured dose in water from a two-dimensional diode array at the same depths. The ability of the BSS-EPID system to operate independently of detector position was demonstrated by comparing the dose reconstruction of a 10 × 10 cm² field using different detector offsets to that measured by a two-dimensional diode array. Results: The shielding of the BSS-EPID was found to be effective, with more than 99% of pixels showing less than 0.5% change due to the presence of the support arm and at most a 0.2% effect on the central axis for 2 × 2 cm² fields to fully open 30 × 40 cm² images. The dose model was shown to accurately reconstruct measurements of dose in water using BSS-EPID images with average γ pass rates (2%, 2 mm criteria) of 92.5%, 98.7%, 97.4%, and 97.2% at depths of 2, 5, 10, and 20 cm, respectively, when compared to two-dimensional diode array measurements. When using 3%, 3 mm γ criteria, the average pass rate was greater than 97% at all depths. Reconstructed dose in water for a 10 × 10 cm² field measured with detector offsets as large as 10 cm agreed with each other and two-dimensional diode array measurements within 0.9%. Conclusions: The modified BSS-EPID and associated dose model provide an improved system for dosimetry measurements using EPIDs. Several important limitations of the current hardware and software are addressed by this system.
- Subject
- medical imaging; image guided radiation therapy; calibration; backscatter; image reconstruction; EPID; dosimetry
- Identifier
- http://hdl.handle.net/1959.13/1307923
- Identifier
- uon:21566
- Identifier
- ISSN:0094-2405
- Language
- eng
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