- Title
- Impact of backscattered radiation from the bunker structure on EPID dosimetry
- Creator
- Rowshanfarzad, Pejan; Sabet, Mahsheed; O'Connor, Daryl J.; Greer, Peter B.
- Relation
- NHMRC.569211
- Relation
- Journal of Applied Clinical Medical Physics Vol. 13, Issue 6, p. 91-100
- Publisher Link
- http://dx.doi.org/10.1120/jacmp.v13i6.4024
- Publisher
- American College of Medical Physics
- Resource Type
- journal article
- Date
- 2012
- Description
- Amorphous silicon electronic portal imaging devices (EPIDs) have been investigated and used for dosimetry in radiotherapy for several years. The presence of a phosphor scintillator layer in the structure of these EPIDs has made them sensitive to low-energy scattered and backscattered radiation. In this study, the backscattered radiation from the walls, ceiling, and floor of a linac bunker has been investigated as a possible source of inaccuracy in EPID dosimetry. EPID images acquired in integrated mode at discrete gantry angles and cine images taken during arcs were used with different field setups (18 × 18 and 10 × 10 cm² open square fields at 150 and 105 cm source-to-detector distances) to compare the EPID response at different gantry angles. A sliding gap and a dynamic head-and-neck IMRT field and a square field with a 15 cm thick cylindrical phantom in the beam were also investigated using integrated EPID images at several gantry angles. The contribution of linac output variations at different angles was evaluated using a 2D array of ion chambers. In addition, a portable brick wall was moved to different distances from the EPID to check the effect at a single angle. The results showed an agreement of within 0.1% between the arc mode and gantry-static mode measurements, and the variation of EPID response during gantry rotation was about 1% in all measurement conditions.
- Subject
- linac; EPID; dosimetry; bunker; backscatter
- Identifier
- http://hdl.handle.net/1959.13/1062502
- Identifier
- uon:17097
- Identifier
- ISSN:1526-9914
- Language
- eng
- Full Text
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