206 Petrovic B et al. / Verification of EDW in three ways The peripheral dose of EDW field is half the dose of the hard wedged field. The reason for that lies in scatter outside the hard wedged field, due to the interaction of the beam with the material of the me- chanical wedge. Clinically, this is an advantage of EDW wedged field. The wedge angle is better pre- served for EDW than for hard wedges at all depths. The profile dose measured by EPID outside the field (peripheral dose) was much larger than the one measured by the CA 24 linear array. This is characteristic of all angles and for all field sizes. The reason for that as explained in the literature, might be due to the difference in absorption of low energy photons which appears in the material of the high Z. Spectrum of the photons is changed with the distance from the central axis, and region outside the field has only a scatter radiation. That is why the difference in profiles outside the field can be assumed to come from the difference of low energy photons of other dosimetrical methods and sensitive material of EPID detectors. Practically, all measurement techniques of EDW give very satisfactory results in terms of the agree- ment within PDDs and profiles (Figure 5). Still, standard dosimetric measurements cannot be un- derestimated, and EPID implemented as verifica- tion tool in terms of implementation of a new tech- nique in the department. References 1. Klein E. Treatment planning for enhanced dynamic wedge with the CMS Focus/Modulex treatment planning system. Med Dosim 1997; 22: 213-14. 2. Miften M, Wiesmeyer M, Beavis A, Takahashi K, Broad S. Implementation of enhanced dynamic wedge in the Focus RTP system. Med Dosim 2000; 25: 81-6. 3. Gossman MS, Robertson MA, Lawson RC. Correlation between detector array measurements and a computer algorithm for enhanced dynamic wedge. Med Dosim 2007; 32: 211-15. 4. C series Clinac Enhanced Dynamic Wedge Implementation Guide. Palo Alto: Varian Medical Systems; 2002. 5. Brady LW, Heilmann HP, Molls M. New technologies in radiation oncology. Springer Verlag Berlin Heidelberg; 2006. 6. PortalVision Users Guide: Reference Manual for aS500 PortalVision. Palo Alto: Varian Medical Systems; 2003. 7. Berger L, Francois P, Gaboriaud G, Rosenvald JC. Performance optimization of the Varian aS500 EPID system. J Appl Clin Med Phys 2006; 7: 105-114. 8. Greer PB, Barnes MP. Investigation of an amorphous silicon EPID for meas- urement and quality assurance of enhanced dynamic wedge. Phys Med Biol 2007; 10: 1075-87. 9. Menon GV, Sloboda RS. Quality assurance measurements of a-si EPID per- formance. Med Dosim 2004; 29: 11-17. 10. Bailey DW, Kumaraswamy L, Podgorsak MB. A fully electronic intensity- modulated radiation therapy quality assurance (IMRT QA) process imple- mented in a network comprised of independent treatment planning, record and verify, and delivery systems Radiol Oncol 2010; 44: 124-30. 11. Curtin-Savard A; Podgorsak EB. An electronic portal imaging device as phys- ics tool. Med Dosim 1997; 22: 101-5. 12. Greer PB, Popescu CC. Dosimetric properties of an amorphous silicon elec- tronic portal imaging device for verification of dynamic intensity modulated radiation therapy. Med Phys 2003; 30:1618-27. 13. Winkler P, Hefner A, Georg D. Dose-response characteristics of amorphous silicon EPID. Med Phys 2005; 32: 95-105. 14. Heikal AA, Wachowicz K, Thomas SD, Fallone BG. A phantom to assess the accuracy of tumor delineation using MRSI. Radiol Oncol 2008; 42: 232-9. Radiol Oncol 2010; 44(3): 199-206.