Abstract
We have automated the determination of the placement location of the dosimetry ion chamber within intensity‐modulated radiotherapy (IMRT) fields, as part of streamlining the entire IMRT quality assurance process. This paper describes the mathematical image‐processing techniques to arrive at the appropriate measurement locations within the planar dose maps of the IMRT fields. A specific spot within the found region is identified based on its flatness, radiation magnitude, location, area, and the avoidance of the interleaf spaces. The techniques used include applying a Laplacian, dilation, erosion, region identification, and measurement point selection based on three parameters: the size of the erosion operator, the gradient, and the importance of the area of a region versus its magnitude. These three parameters are adjustable by the user. However, the first one requires tweaking in extremely rare occasions, the gradient requires rare adjustments, and the last parameter needs occasional fine‐tuning. This algorithm has been tested in over 50 cases. In about 5% of cases, the algorithm does not find a measurement point due to the extremely steep and narrow regions within the fluence maps. In such cases, manual selection of a point is allowed by our code, which is also difficult to ascertain, since the fluence map does not yield itself to an appropriate measurement point selection.PACS numbers: 87.53.Xd, 87.66.Cd, 87.57.Nk
Highlights
For every patient who undergoes intensity-modulated radiotherapy (IMRT) treatment, our physics team performs a series of quality assurance (QA) tests
A spherical ion chamber (0.125 cm3) is used for the absolute measurements, and Kodak EDR-2 films are used for relative dose maps
We have allowed for the possibility of failure of this code in extreme cases, in which cases the user can manually select a position for the ion chamber placement
Summary
For every patient who undergoes intensity-modulated radiotherapy (IMRT) treatment, our physics team performs a series of quality assurance (QA) tests These tests are to ensure proper delivery of radiation dose to the appropriate geometrical sites within the patient. One of the two depths (7 cm) is for absolute dosimetry verification at a single point, and the other one (6 cm) is for comparing the computed isodose patterns with those of the irradiated films. A spherical ion chamber (0.125 cm3) is used for the absolute measurements, and Kodak EDR-2 films are used for relative dose maps. These measurements are performed during the same irradiation session for each beam. For the isodose profile comparison, we are developing image subtraction software, as well as a system based on principal component analysis
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