Monitor chamber backscatter for intensity modulated radiation therapy using multileaf collimators.
Authors
Hounsell, Alan RAffiliation
North Western Medical Physics, Christie Hospital NHS Trust, Manchester, UK. prsarh@dalpha2.cr.man.ac.ukIssue Date
1998-02
Metadata
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Backscattered radiation into the machine monitor chamber can affect the machine output variation, with changes in field size and shape. For intensity modulated radiation therapy (IMRT) where many field, which may have small dimensions, are summed to give an intensity modulated field, the magnitude of backscatter will be different due to both the backscattering surface area changing, and the delivered monitor units being larger than for the equivalent static field. The effect of backscatter variation with field size for a Philips SL15 accelerator has been investigated at 8 MV for static and IMRT fields both in the standard clinical operating condition where an anti-backscatter plate is fitted, and also for a case where the anti-backscatter plate has been removed. The results show that in the absence of the anti-backscatter plate the variation in output between a 4 cm by 4 cm field and a 40 cm by 40 cm field size due to backscattered radiation was 5% for static fields. The anti-backscatter plate reduced this variation to less than 1%. When the accelerator operated in IMRT mode, with the backscatter plate in place, changes in the output due to additional backscattered radiation were less than 0.3%. With the backscatter plate removed, the outputs were lower, indicating the presence of additional backscattered radiation. It can be concluded that for the Philips MLC and SL accelerator with its anti-backscatter plate, the effects of backscattered radiation can be ignored for both static and IMRT fields.Citation
Monitor chamber backscatter for intensity modulated radiation therapy using multileaf collimators. 1998, 43 (2):445-54 Phys Med BiolJournal
Physics in Medicine and BiologyDOI
10.1088/0031-9155/43/2/017PubMed ID
9547177Type
ArticleLanguage
enISSN
0031-9155ae974a485f413a2113503eed53cd6c53
10.1088/0031-9155/43/2/017