EDW profiles obtained by EPID in comparison with the same measured by the linear array dif- fer around 1%, max up to 2%, within the field (Table 1). At the edges of the fields, the EPID profiles were having a larger gradient (dose fall down) than the profiles obtained by other meth- ods. This applies to all wedge angles. A dose measured by EPID outside the field (pe- ripheral dose) was much larger than the one meas- ured by CA 24 linear array. This is characteristic for all angles and for all field sizes. (Figure 2) Profiles measured by EPID in comparison to open beam profiles measured by ionization chamber EDW profiles imaged by EPID in the perpen- dicular direction to the movement of the jaw, were also examined, and compared to the open field profiles, which were measured during com- missioning of the machine, by CC13 ionization chambers. A very good agreement was found (Table 2, Figure 3). This is not the case with the profiles of hard wedged fields, measured also in the non-wedged direction, where the interaction of the beam with the material of the hard wedge (beam hardening effect), influences the shape of the profile (a hard wedged profile demonstrates a decrease in dose at the field edges in compari- son with the EDW and open field profile in non wedged direction). Profiles of EDW field measured by linear array in comparison of hard wedges profiles measured by ionization chambers EDW linear array profiles to hard wedges do dif- fer more in all cases, but that was expected due to the physical differences of two techniques (Figu- re 4) Profiles of EDW field measured by linear array in comparison to the calculation of XIO CMS TPS In most cases, the dose values on profiles differ around 0.5%, within the field, while outside the field it seems that XIO underestimates the periph- eral doses by factor of 2. 160 140 120 100 ()80 % D P 60 40 20 0 15 MV, 10x10 wedge 60 deg, depth 30 mm CA 24 hard portal XIO Petrovic B et al. / Verification of EDW in three ways 205 distance from central axis (mm) FIGURE 5. 15 MV profiles for a 10 cm x10 cm field, 60 deg wedge, build up (four methods of measurements and calculations). EDW wedge factors EDW wedge factors are the strong functions of the field size. This is proved by the measurements of wedge factors of EDW fields, and by the calcula- tion of WF in the treatment planning system. This, of course, does not apply to the hard wedge whose dependence of the field size is almost negligible. This is due to the fact that mechanical wedges are always placed in the same position on the tray of the accelerator, and because the central beam al- ways passes through the same thickness of the wedge, it does not matter what the field size is ac- tually set (Table 3). Discussion For the quality assurance (QA) in radiotherapy we can use in vivo or in vitro methods with phantoms.14 The second one can be used for for routine QA or for reference measurements. The basic conclu- sion of our study would be that EPID aS1000 can be used for the routine QA and for EDW verifica- tion, but not for commissioning, only for regular QA checks. The conclusion would also be that the implemented dose calculation algorithm well de- scribes the EDW treatment. Radiol Oncol 2010; 44(3): 199-206.