Comparison of dosimetric characteristics of virtual and physical wedges and quality control of virtual wedge

The purpose of this study is to evaluate the reproducibility of dose profiles created with virtual wedge, to compare dose profiles created in fields with virtual and physical wedge and to establish the required quality control program for virtual wedge.The dose profiles in fields with virtual and physical wedge were measured with film dosimeters and MP3 water phantom at a ninety centimeter source-surface distance (SSD) and 10 cm depth. PTW Semiflex ion chambers were used in the MP3 water phantom. Within the scope of the quality control program, maximum monitor units (MUmax) were calculated using the attenuation equations, and daily output measurements were carried out at a hundred centimeter SSD on 20x20 cm2 field with PTW QC6Plus quality control dosimetric system.It was observed that dose profiles obtained with 6 MV-X energy on 10X10 cm2 30º and 45º virtual wedged fields were reproducible. Dose profiles created on 10X10 cm2 30º and 45º physical and virtual wedged fields with the same wedge angle have a maximum difference of -2.6% and 2.3% at the toe area and a maximum difference of -0.5% and -0.7% at the heel area, for the 30º and 45º wedges, respectively. No difference was observed between the MUmax values calculated with the attenuation equations and linear accelerator software. A difference of maximum -2% from reference values was observed in daily output measurements.This study has shown that virtual wedges can be safely used in radiotherapy with the establishment of quality control programs. Due to the differences in dose profiles in fields with virtual and physical wedges, these differences must be taken into consideration when using one in place of the other. Again, with a suitable quality control program, the stability of the dose profiles obtained from fields with virtual wedge can be tested. Furthermore, it is recommended that routine application of virtual wedges should be implemented after the dose profiles of virtual wedges obtained by treatment planning systems are tested.Keywords: Wedge techniques, quality control, attenuation equation