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Two‐dimensional ionization chamber arrays for IMRT plan verification
Author(s) -
Poppe Bjoern,
Blechschmidt Arne,
Djouguela Armand,
Kollhoff Ralf,
Rubach Antje,
Willborn Kay C.,
Harder Dietrich
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 - 10.1118/1.2179167
Subject(s) - ionization chamber , quality assurance , dosimetry , beam (structure) , optics , physics , ionization , nuclear medicine , computer science , engineering , medicine , ion , operations management , external quality assessment , quantum mechanics
In this paper we describe a concept for dosimetric treatment plan verification using two‐dimensional ionization chamber arrays. Two different versions of the 2D‐ARRAY (PTW‐Freiburg, Germany) will be presented, a matrix of 16 × 16 chambers (chamber cross section 8 mm × 8 mm ; the distance between chamber centers, 16 mm ) and a matrix of 27 × 27 chambers (chamber cross section 5 mm × 5 mm ; the distance between chamber centers is 10 mm ). The two‐dimensional response function of a single chamber is experimentally determined by scanning it with a slit beam. For dosimetric plan verification, the expected two‐dimensional distribution of the array signals is calculated via convolution of the planned dose distribution, obtained from the treatment planning system, with the two‐dimensional response function of a single chamber. By comparing the measured two‐dimensional distribution of the array signals with the expected one, a distribution of deviations is obtained that can be subjected to verification criteria, such as the gamma index criterion. As an example, this verification method is discussed for one sequence of an IMRT plan. The error detection capability is demonstrated in a case study. Both versions of two‐dimensional ionization chamber arrays, together with the developed treatment plan verification strategy, have been found to provide a suitable and easy‐to‐handle quality assurance instrument for IMRT.