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Dosimetric problems at low monitor unit settings for scanned and scattering foil electron beams
Author(s) -
Das Indra J.,
Harrington James C.,
Akber Syed F.,
Tomer Alan F.,
Murray James C.,
Cheng CheeWai
Publication year - 1994
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.597328
Subject(s) - dosimetry , monitor unit , beam (structure) , linearity , scattering , percentage depth dose curve , flatness (cosmology) , linear particle accelerator , absorbed dose , optics , laser beam quality , dose profile , physics , foil method , materials science , ionization chamber , nuclear medicine , radiation , laser , ionization , laser beams , medicine , ion , cosmology , quantum mechanics , composite material
Electron beam dosimetry at low monitor unit (MU) settings is important for dosimetric applications. Dose linearity, beam flatness, and beam energies were studied at low MU settings with various dose rates for different types of linear accelerators. It is observed that for the scattering foil units, the dose/MU is a smooth function of MU for all beam energies. Discrepancies in dose/MU are highest at the lowest MU. Significant variation (5%–245%) in dose linearity is observed among various linear accelerators at low MU settings. Dose rate has no effect on the dose linearity for all energies for the scattering foil units tested. On the contrary, for the scanned beam, there is no predictable pattern as dose/MU is random in nature and varies with time and beam energy. The maximum dosimetric error is observed for the highest energy beam where the beam width is most narrow. Using film, the beam uniformity was noticed to be very poor at low MU and high energy for scanned beams. The beam uniformity and dose linearity are random at low MU due to the random nature of the scan cycle. Under the adverse conditions, the deviation in dosimetric parameters was observed up to 200 MU.