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SU‐E‐T‐60: Evaluation of a Two‐Dimensional Ionization Chamber Array for Proton Beam Dosimetry
Author(s) -
Stelljes TS,
van Goethem M,
Brandenburg S,
Willborn K,
Poppe B
Publication year - 2013
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 - 10.1118/1.4814495
Subject(s) - ionization chamber , dosimetry , beam (structure) , optics , collimator , proton , ionization , physics , absorbed dose , proton therapy , materials science , radiation , nuclear medicine , nuclear physics , ion , medicine , quantum mechanics
Purpose: The application of the two‐dimensional ionization chamber array Octavius 729xdr (PTW‐Freiburg, Germany) in proton beam dosimetry, consisting of 729 vented ionization chambers arranged in a 27 × 27 cm 2 matrix, equivalent to the 2D‐Array 729 used for photon beams 1 , is investigated. Methods: Measurements were carried out with a double scattered 150 MeV proton beam at the AGOR cyclotron at the KVI (Rijksuniversiteit, Groningen — Netherlands). A water bellow with adjustable depth ranging from 10 to 300 mm was placed in the beam line directly behind the collimator for built‐up. The stability, linearity and output factors of the array for circular fields produced using collimators with sizes of 3, 5,7 and 10 cm in diameter were investigated. PDD profiles with a Farmer chamber (type 30010, PTW‐Freiburg, Germany) and the array were measured by stepwise increasing the water bellow's depth. Results: The variation in measurement signal of the 729xdr array was less than 0.2 % after preirradiation with 2 Gy. The linearity of the array was found to be excellent. Output factors showed the expected small variations for circular field sizes. PDDs measured with the array and a Farmer chamber showed good agreement in the region of the Bragg peak with the array slightly underestimating the dose in the built‐up region. Conclusion: The first measurements with the Octavius 729xdr array show the potential of a two‐dimensional ionization chamber array in proton beam dosimetry. The dosimetric properties and the applications of the array in clinical dosimetry will be investigated in more detail in future studies.References1B. Poppe, A. Blechschmidt, A. Djouguela, “Two‐dimensional ionization chamber arrays for IMRT plan verification,” Med. Phys. 33, 1005–1015 (2008)