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Verification of segmented beam delivery using a commercial electronic portal imaging device
Author(s) -
CurtinSavard Arthur J.,
Podgorsak Ervin B.
Publication year - 1999
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 - 10.1118/1.598581
Subject(s) - multileaf collimator , ionization chamber , collimator , dosimetry , imaging phantom , linear particle accelerator , calibration , intensity modulation , optics , beam (structure) , quality assurance , monitor unit , planar , physics , computer science , nuclear medicine , ionization , engineering , computer graphics (images) , medicine , ion , external quality assessment , quantum mechanics , phase modulation , phase noise , operations management
In modern radiotherapy, three‐dimensional conformal dose distributions are achieved through the delivery of beam ports having precalculated planar distributions of photon beam intensity. Although sophisticated means to calculate and deliver these spatially modulated beams have been developed, means to verify their actual delivery are relatively cumbersome, making equipment and treatment quality assurance difficult to enforce. An electronic portal imaging device of the scanning liquid ionization chamber type yields images which, once calibrated from a previously determined calibration curve, provide highly precise planar maps of the incident dose rate. For verification of an intensity‐modulated beam delivered in the segmented approach with a multileaf collimator, a portal image is acquired for each subfield of the leaf sequence. Subsequent to their calibration, the images are multiplied by their respective associated monitor unit settings, and summed to produce a planar dose distribution at the measurement depth in phantom. The excellent agreement of our portal imager measurements with calculations of our treatment planning system and measurements with a one‐dimensional beam profiler attests to the usefulness of this method for the planar verification of intensity‐modulated fields produced in the segmented approach on a computerized linear accelerator equipped with a multileaf collimator.