Investigation of the Field Size Effect on Wedge Field Isodose Curves Angle for Two Energies; 6MV & 18MV, produced by VARIAN 2100C Linac

Nowadays, considerable development in equipments and treatment plannings in radiotherapy were achieved, which have resulted the accurate treatment methods. Despite of these developments, in most clinics, conventional treatment methods are ever using. One of these conventional treatments is application of physical wedge. One of the wedge field parameters is wedge angle. The angle of horizontal line with tilt Isodose curve, which is occurred specific field size and depth, is wedge angle. Treatment plannings are implemented by wedge angle. In this study, variation of wedge angle for different field size were measured dosimetric and mathematical equation. MATERIALS AND METHODS: For the wedge fields with a dimension of 6×6 cm2 to 20×20 cm2 , wedge angle for two energies 6MV and 18MV was measured by dosimetric method. For constituting Isodose curve, convention wedges used in radiotherapy with 15,30,45 & 60 degree nominal wedge angle, were applied. Also theoretical method for calculated wedge angle expressed was assayed fore VARIAN2100C Linac. In this method, Isodose curve slope calculates indirectly by profile and percent depth dose curves. Profile, PDD and Isodose curves were drawn for all fields and tilt of Isodose curve in 10cm of depth , according to international definitions was considered as the wedge angle. Data were obtained from theoretical equation of wedge angle and compared with dosimetric data. RESULTS: With increasing the field size, wedge angle is also increased. In field size of 6×6 cm2 wedge angle shows highest difference with nominal wedge angle, so that this difference for 45° wedge in 6MV is 14.7 degrees. Highest difference for field size of 10×10 cm2 , as the standard field to wedge angle definition, in 45° wedge at 6MV is obtained 9.2 degrees. Wedge angle results using mathematical equation , in highest difference in comparison dosimetric methods shows 4 degrees. DISCUSSION AND CONCLUSION: Wedge angle varies by different field size. In order to enhance dose delivery in conventional radiotherapy, it is necessary to use appropriate wedge which constitute desire slop of Isodose angle in that field size.

کلیدواژه ها:

profile curve ، PDD curve ، Isodose curve ، wedge angle