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Patient position verification using small IMRT fields
Author(s) -
Bol G. H.,
van der Heide U. A.,
Nederveen A. J.,
Kotte A. N. T. J.,
Lagendijk J. J. W.
Publication year - 2006
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 - 10.1118/1.2207251
Subject(s) - imaging phantom , matching (statistics) , position (finance) , computer vision , computer science , template matching , artificial intelligence , projection (relational algebra) , volume (thermodynamics) , image guided radiation therapy , image registration , medical imaging , image (mathematics) , nuclear medicine , mathematics , algorithm , medicine , physics , statistics , finance , quantum mechanics , economics
A commonly used approach to quantify and minimize patient setup errors is by using electronic portal imaging devices (EPIDs). The position of the tumor can be verified indirectly by matching the bony anatomy to a reference image containing the same structures. In this paper we present two off‐line methods for detecting the position of the bony anatomy automatically, even if every single portal image of each segment of an IMRT treatment beam contains insufficient matching information. Extra position verification fields will no longer be necessary, which reduces the total dose to the patient. The first method, the stack matching method (SMM), stacks the portal image of each segment of a beam to a three dimensional (3D) volume, and this volume is subsequently used during the matching phase. The second method [the averaged projection matching method (APMM)], is a simplification of the first one, since the initially created volume is reduced again to a 2D artificial image, which speeds up the matching procedure considerably, without a significant loss of accuracy. Matching is based on normalized mutual information. We demonstrate our methods by comparing them to existing matching routines, such as matching based on the largest segment. Both phantom and patient experiments show that our methods are comparable with the results obtained from standard position verification methods. The matches are verified by means of visual inspection. Furthermore, we show that when a distinct area of 40– 60cm 2of the EPID is exposed during one treatment beam, both SMM and APMM are able to deliver a good matching result.