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Sampling considerations for intensity modulated radiotherapy verification using electronic portal imaging
Author(s) -
Evans Philip M.,
Partridge Mike,
SymondsTayler J. Richard N.
Publication year - 2001
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 - 10.1118/1.1354626
Subject(s) - multileaf collimator , duty cycle , intensity modulation , intensity (physics) , sampling (signal processing) , nuclear medicine , medical imaging , collimator , frame (networking) , frame rate , radiation therapy , dosimetry , optics , beam (structure) , computer science , linear particle accelerator , physics , medicine , radiology , artificial intelligence , detector , voltage , phase modulation , quantum mechanics , telecommunications , phase noise
A model has been developed to describe the sampling process that occurs when intensity modulated radiotherapy treatments (delivered with a multileaf collimator) are imaged with an electronic portal imaging device that acquires a set of frames with a finite dead‐time between them. The effects of the imaging duty cycle and frame rate on the accuracy of dosimetric verification have been studied. A frame interval of 1 s with 25%, 50% and 75% duty cycle, and a 50% duty cycle with frame intervals of 1, 2, 4, 8, and 16 s have been studied for a smoothly varying hemispherical intensity profile, and a 50% duty cycle with frame intervals of 1, 2, 4, and 8 s for a pixellated distribution. In addition an intensity modulated beam for breast radiotherapy has been modeled and imaged for 0.33 s frame time and 1, 2, and 3 s frame separation. The results show that under sparse temporal sampling conditions, errors of the order of 10% may ensue and occur with an oscillatory pattern. For the beams studied, imaging with a 1 or 2 s frame interval resulted in small errors at the 1%–2% level, for all duty cycles shown.