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Impact of multileaf collimator leaf positioning accuracy on intensity modulation radiation therapy quality assurance ion chamber measurements
Author(s) -
Woo M. K.,
Nico A.
Publication year - 2005
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 - 10.1118/1.1901843
Subject(s) - multileaf collimator , ionization chamber , linear particle accelerator , quality assurance , intensity modulation , dosimetry , collimator , reproducibility , imaging phantom , medical physics , optics , nuclear medicine , beam (structure) , radiation treatment planning , materials science , radiation therapy , physics , ionization , ion , medicine , mathematics , radiology , phase modulation , statistics , external quality assessment , pathology , quantum mechanics , phase noise
Quality assurance (QA) procedures for intensity modulation radiation therapy (IMRT) usually involve an ion chamber measurement in a phantom using the beam configuration of the actual treatment plan. In our QA procedures it was observed that the degree of agreement between the measurement and the calculation could vary from plan to plan, from linac to linac, as well as over time, with a discrepancy up to 8%. In this paper we examine one aspect of the process which can contribute to such poor reproducibility, namely, the leaf end position accuracy. A series of measurements was designed to irradiate an ion chamber using small beam segments where one multileaf collimator (MLC) edge covers half of the chamber. It was shown that the reproducibility varied up to 13%, which provides a possible explanation for the observed discrepancies above. A useful tool was also developed to measure ionization signals from individual segments of an IMRT sequence. In addition, an understanding of the leaf end position variations offers some insight into the overall quality of an IMRT dose distribution.