Schematic drawings of the 2D-ARRAYs commercially available. Left: version 1 (PTW type 10017), ionization chambers. Right: version 2 (PTW type 10024), chambers.
(a) Scheme of the collimation of a slit beam that had a full half-width of in the ISO plane. A: Upper collimator, slit width corresponding to in the ISO plane. B: Lower collimator (MLC), one leaf pair opening with a slit length of in the ISO plane. C: Tertiary collimator (cast metal), positioned in the accessory holder, slit width . (b) Profile of the slit beam in the ISO plane, measured by film dosimetry. Squares: film placed on top of a PMMA phantom, no preabsorber. Circles: film at depth in PMMA.
A comparison of a measured and planned Virtual Wedge profile (, ). Points: 2D-ARRAY (version 2); line: Dose profile measured with ionization chamber.
Field-size-dependent output factors for photon radiation, measured with different detectors at a depth of in a RW3 phantom (source-to-surface distance , backscatter material). At the small field sizes, the volume effect of the ionization chambers is clearly detectable.
Lateral response functions of types 1 and 2 of 2D-ARRAYs measured by slit scanning with a slit of half-width. The gray areas denote the positions of the ridges between two adjacent chambers.
Dose profile at the edge of a photon field at in the in-plane direction. A comparison of the true profile (diode values), the true profile convolved with the response function of the single chamber of the 2D-ARRAY, and the measured values of a single chamber of the 2D-ARRAY obtained by stepwise scanning across the dose distribution. (a) 2D-ARRAY version 1; (b) 2D-ARRAY version 2.
Work flow chart of the comparison between expected and measured readings of the 2D-ARRAY. The procedure is shown for version 1 (type 10017).
Dose profile along the dashed line marked in the insert. Solid line: dose values from planning system. Dotted line: profile from film measurement. Squares: expected readings of the 2D-ARRAY (version 1). Crosses: measured values . The visible shift of the expected and measured readings from the profile is due to dose gradients in the direction vertical to the scanning line.
Chamber readings failing the gamma-index criterion for the 2D-ARRAY’s versions 1 and 2. Black squares: chambers failing the criterion with , . Lines: isodoses from the planning system.
Left: MLC shape of a segment of the IMRT field with introduced error. Solid line: segment without error. Dashed line: artificial MLC error of . The relative weight of this segment to the overall field is 30%. Right: chambers failing to meet the gamma-index criterion after irradiation of the sequence (black square), with and . Lines: isodoses from a planning system (2D-ARRAY, version 2).
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