期刊
MEDICAL PHYSICS
卷 30, 期 3, 页码 341-347出版社
WILEY
DOI: 10.1118/1.1544678
关键词
IMRT; quality assurance; small field dosimetry; volume effect
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 cm(3) 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 cm(3) 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 cm(2) 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. 2003 American Association of Physicists in Medicine.
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