I2-4 - Sedma Nacionalna Konferencija so Me|unarodno U~estvo...

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DOSE PROFILES IN NON-WEDGED DIRECTION FOR VARIAN EDW Zoran Stefanovski 1 , Sonja Petkovska 1 , Dusko Lukarski 1 1 Institute of Radiotherapy and Oncology, Medical Faculty, Vodnjanska 17, 1000 Skopje, zoran1@ukim.edu.mk Abstract - Purpose: Varian Enhanced Dynamic Wedge is a standard tool in providing high quality radiation therapy. The purpose of this paper is to verify some dosimetric characteristics of Varian EDW. We checked non-wedge profiles for the 60 ˚ wedge and compute the field flatness from the ex- perimental data. Methods and Materials: The measurements were made on a Varian 23EX accelerator using a water phantom and an ion chamber array. During the measurements the chamber array was placed along the wedged direction and for each meas- urement it was moved in steps of 2 cm off centre along the non-wedge direction. The measurements were made for different field sizes and different depths in water. Thus obtained data in wedge di- rection were transferred in data in non-wedge di- rection and calculated and graphed in a spread- sheet program. Results: The dose profiles in non-wedge direction closely resemble the dose profiles of open fields. The flatness of the non-wedged profiles was within 1% of those of open profiles. Because of discrete nature of the chamber array our estimation is that the flatness is even better especially for the heeled part of EDW. Discussion and Conclusion: EDW needs special kind of QA tests because of its virtual nature and unavailability of visual inspection. This kind of measurements can be one more test that assures the user that the EDW is safe and ready for clini- cal use. Key Words: Enhanced Dynamic Wedge, Dose Profiles, Dosimetry 1. INTRODUCTION Wedge filters represent the main way of beam modu- lation in conformal radiation therapy. While hard (mechanical) wedges are being applied from the be- ginning of high energy photons radiotherapy, dy- namic (also called virtual) wedges are only recently introduced in linear accelerators for radiotherapy [1]. Through computer control of Y collimator jaw mo- tion Varian introduced this method under the name Enhanced Dynamic Wedge (EDW) [6]. Their imple- mentation in the accelerators is enabled through the segmented treatment tables (STTs). In these tables monitor units are defined as a function of the position of the moving jaw. Only 60 o wedge is defined using predefined, so called, Golden STT. All other wedge angles can be derived combining open field and wedged field irradiation. Dynamic wedges have several advantages over the hard ones. One drawback of a hard wedge is that the photon energy spectrum is hardened after passing through the wedge material, and thus the dosimetric properties of the beam energy fluence are altered.
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This note was uploaded on 02/18/2010 for the course ITK ETF113L07 taught by Professor Popovskiborislav during the Spring '10 term at Pacific.

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I2-4 - Sedma Nacionalna Konferencija so Me|unarodno U~estvo...

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