Petrovic B et al. / Verification of EDW in three ways 203 TABLE 3. WF measured for the angle of 60°, and field sizes 4x4 cm2, 10x10 cm2, 15x15 cm2, 20x20 cm2, 30x30 cm2 using the energy of 15M Y1 (cm) Y2(cm) Measured WF Hard wedge WF 2 5 7.5 10 20 2 5 7.5 10 10 0.892 0.713 0.596 0.499 0.343 TPS WF 0.882 0.689 0.575 0.483 0.345 X(cm) 4 10 15 20 30 The image acquired by EPID, which results from each EDW field irradiation, is 2D image, with the different pixel values and is closely related to the intensity map of the EDW field. The pixel values carry information about the intensity of the signal within the pixel area. Pixels lying on lines crossing the central axis pixel are creating in plane and cross plane profiles. One profile is in the direction of the moving jaw, creating the wedged distribution, and another one is the perpendicular to the direction of the moving jaw. Other pixels are lying off axis, and can be used to create 3D image of a wedged field. In order to extract useful information about the profiles, the central axis pixel value is assigned value 100. All other pixels got then a relative value, depending on the ratio of the original pixel value on central axis, and elsewhere in plane and cross plane profiles. The series of relative pixel values on both profiles creates profiles comparable to other methods of measurements. External beam treatment planning calculations The treatment planning system used for this pur- pose was XIO CMS v. 4.2.0, convolution algorithm. Virtual phantom of the size of the big Blue phan- tom (used for measurements in water), was de- fined in the TPS, and the electron density of water assigned to the inner space of the phantom. The EDW beam was created with the collimator and gantry orientation as in water and EPID measure- ments, and appropriate field size, wedge angle, weight point definition, normalization, etc, imi- tating the measurements under real conditions in water. The resulting calculated plan was analyzed taking into consideration the depth dose curve and profiles on determined depths (build up, 5 cm, 10 cm and 20 cm). Dose values were read from the Dose Profile in the menu of the treatment planning space of XIO, on 5 mm distance along the profile of the field. 120 100 80 ) % ( D D P 60 40 20 0 140 120 100 80 ) % ( D P60 40 20 0 0.431 0.437 0.444 15 MV 10x10 wedge 60 deg 15 MV, 10x10 wedge 60 deg depth 30 mm hard open CA24 XIO CA 24 portal ,04 ,101 ,197 ,302 ,402 98 ,4 ,04 6 , 701 ,798 ,903 100 ,0961 ,1220 ,1298 ,1430 105 ,6041 01 ,17 ,99 17 ,04 19 ,99 19 ,04 21 ,99 21 ,97 22 ,20 24 ,01 25 ,79 25 ,01 27 ,89 27 ,02 29 ,10 30 depth (mm) FIGURE 1. PDD of 10 cm x 10 cm field, 15 MV, wedge 60 deg. distance from central axis (mm) FIGURE 2. EPID profile vs CA24 profile, 10 cm x10 cm field, wedge 60 deg. Radiol Oncol 2010; 44(3): 199-206.