202 Petrovic B et al. / Verification of EDW in three ways TABLE 2. Open field profiles in 3 cm build up vs EPID profiles in direction perpendicu- lar to the movement of Y jaw, 10x10 cm2 field Materials and methods Crossline (mm) Open 15deg EDW 30 deg EDW 45deg EDW 60deg EDW -110 -105 -100 -95 -90 -85 -80 -75 -70 -65 -60 -55 -50 -45 -40 -35 -30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 1.3 1.3 1.5 1.7 2.0 2.2 2.7 3.3 4.0 5.4 9.2 26.1 71.2 96.5 100.9 102.2 102.3 101.9 101.8 101.1 100.5 99.7 100.0 100.6 101.2 101.5 101.9 102.5 102.9 102.6 100.5 96.2 74.1 22.5 8.3 5.1 4.1 3.1 2.6 2.3 1.9 1.6 1.6 1.4 1.2 2.8 3.1 3.2 3.8 4.3 5.1 6.0 6.7 7.8 9.3 11.0 13.9 51.0 97.1 99.2 100.1 100.5 100.6 100.5 100.7 100.5 100.4 100.0 100.2 100.2 100.1 100.0 100.0 99.8 99.6 98.8 96.6 48.4 13.4 10.8 9.2 7.8 6.7 5.8 5.1 4.4 3.9 3.4 3.1 2.9 2.8 3.1 3.2 3.8 4.3 5.1 6.0 6.8 7.9 9.3 11.0 14.0 51.5 97.3 99.3 100.2 100.6 100.6 100.6 100.7 100.6 100.4 100.0 100.4 100.2 100.2 100.1 100.1 100.0 99.7 98.8 96.7 46.2 13.4 10.9 9.2 7.9 6.8 5.8 5.1 4.5 3.9 3.5 3.1 2.9 2.9 3.2 3.2 3.8 4.3 5.1 6.0 6.8 7.9 9.3 11.0 14.0 51.6 97.1 99.2 100.1 100.5 100.6 100.6 100.6 100.6 100.4 100.0 100.3 100.2 100.2 100.0 100.1 99.9 99.7 98.8 96.6 48.3 13.5 11.0 9.3 8.0 6.8 5.8 5.2 4.5 4.0 3.5 3.2 2.9 2.9 3.2 3.3 3.9 4.4 5.2 6.1 6.9 8.0 9.4 11.1 14.0 49.7 97.0 99.1 100.0 100.4 100.5 100.5 100.6 100.5 100.3 100.0 100.3 100.2 100.2 100.0 100.0 100.0 99.7 98.9 96.8 50.1 13.6 11.0 9.4 8.0 6.9 6.0 5.3 4.6 4.1 3.5 3.2 3.0 Radiol Oncol 2010; 44(3): 199-206. Linear array CA24 measurements The measurement of enhanced dynamic wedge profiles using a linear chamber array requires the integration of the dose during the entire exposure at each point of measurement. It was done by the CA 24 Scanditronix Welhofer, and two electrom- eters, MD 240 and CU 500E, connected to the PC and OmniPro 6.2A software. The linear array CA 24 consists of 23 ionization chambers, the volume of each is 0.147 cm3, diameter 0.6 cm and active length 0.33 cm. The each two neighbouring cham- bers are placed on 2 cm distance, and their long ax- es are parallel to the central axis of the beam. They are mounted to the holder of the Blue water phan- tom. The main feature of this linear array is that the profiles are measured directly in the water, under the same conditions as measurements of the open field profiles or mechanical wedged field profiles. The beam data was collected according to the guidelines provided by Varian5,6. This consists of measurements of cross profiles and depth dose curves for the maximum (60°) and at least one in- termediate wedge angle, in addition to measure- ments of the output factors. The calculated percentage depth dose curves (PDDs) and profiles were compared with meas- ured data for 15 MV photons at a Varian Clinac 2100C. Square field sizes ranging from 4x4 cm2 to 20x20 cm2 were evaluated with measurements of PDDs and profile curves on few depths (build up, 5 cm, 10 cm, and 20 cm). EPID measurements The features of EPID are described well in the lit- erature.7-13 Portal imager aS1000 was positioned on a source to skin distance (source-EPID surface dis- tance- SSD) 100 cm (not on standard 140 cm). The standard calibration procedure was then applied under this condition. The EDW fields of 4 cm x 4 cm, 10 cm x10 cm, 15 cm x 15 cm, and 20 cm x 20 cm were imaged (with the usage of EPID portal dosimetry mode) for the wedge angles of 15 deg, 30 deg, 45 deg and 60 deg, with the collimator orientation and movement as for CA 24 measurements. The collimator orienta- tion for all measurements was 90 degrees and Y1- IN wedge orientation (Y1 being the dynamic jaw). Linearity of the pixel response with dose was checked, followed by field measurements.