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Delivery of intensity‐modulated radiation therapy with a conventional multileaf collimator: Comparison of dynamic and segmental methods
Author(s) -
Chui ChenShou,
Chan Maria F.,
Yorke Ellen,
Spirou Spiridon,
Ling C. Clifton
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 - 10.1118/1.1418018
Subject(s) - multileaf collimator , intensity (physics) , quality assurance , intensity modulation , computer science , biomedical engineering , medical physics , materials science , beam (structure) , linear particle accelerator , optics , medicine , physics , phase noise , external quality assessment , pathology , phase modulation
Intensity‐modulated radiation therapy (IMRT) can be delivered with a conventional multileaf collimator (MLC), either in dynamic mode (DMLC) or in segmental mode (SMLC, also known as “step‐and‐shoot”). The advantage of DMLC is its ability to deliver the desired intensity profile produced by inverse planning with a high degree of fidelity. The SMLC method, on the other hand, resembles treatment with multiple static fields, and can be more easily verified. However, the use of SMLC requires that the desired profile be approximated by discrete levels of intensity, which may lead to degradation in the delivered dose distribution. Clearly, the results of SMLC delivery depend on the number of levels and the spatial resolution of the intensity distribution. In this work, we compare the DMLC method and the SMLC method employing different numbers of levels and different spatial resolutions. Three disease sites were studied: prostate, nasopharynx, and breast, with three cases for each. In general, a 5‐ to 10‐level SMLC plan produced results comparable to that from a DMLC plan. The target coverage is improved by increasing the number of levels while critical organs are better protected with finer spatial resolutions. The beam‐on‐time (MUs) requirement for SMLC was approximately 20% less than DMLC, but the delivery time (in minutes) was about twice as long. Thus, the choice depends on many factors including machine capability, quality assurance, target coverage, critical organ protection, beam‐on‐time, delivery time, and other clinical considerations.