The volume effect of detectors in the dosimetry of small fields used in IMRT

Laub, W and Wong, T 2003, 'The volume effect of detectors in the dosimetry of small fields used in IMRT', Medical Physics, vol. 30, pp. 341-347.

Document type: Journal Article
Collection: Journal Articles

Title The volume effect of detectors in the dosimetry of small fields used in IMRT
Author(s) Laub, W
Wong, T
Year 2003
Journal name Medical Physics
Volume number 30
Start page 341
End page 347
Total pages 7
Publisher American Institute of Physics
Abstract In this study we investigate the effect of detector size in the dosimetry of small fields and steep dose gradients with a particular emphasis on IMRT measurements. Comparisons of calculated and measured cross-profiles and absolute dose values of IMRT treatment plans are presented. As a consequence of the finite size of the detector that was used for the commissioning of the IMRT tool, local discrepancies of more than 10% are found between calculated cross-profiles of intensity modulated beams and intensity modulated profiles measured with film. Absolute dose measurements of intensity modulated fields with a 0.6 cm3 Farmer chamber show significant differences of more than 6% between calculated and measured dose values at the isocenter of an IMRT treatment plan. Differences of not more than 2% are found in the same experiment for dose values measured with a 0.015 cm3 pinpoint ion chamber. A method to correct for the spatial response of finite-sized detectors and to obtain the "real" penumbra width of cross-profiles from measurements is introduced. Output factor measurements are performed with different detectors and are presented as a function of detector size for a 1 x 1 cm2 field. Because of its high spatial resolution and water equivalence, a diamond detector is found to be suitable as an alternative to other detectors used for small field dosimetry as there are photographic and photochromic film, TLDs, or water-equivalent scintillation detectors.
Subject Biological Physics
DOI - identifier 10.1118/1.1544678
ISSN 0094-2405
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