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J Korean Soc Ther Radiol Oncol > Volume 17(1); 1999 > Article
The Journal of the Korean Society for Therapeutic Radiology and Oncology 1999;17(1): 78-83.
Physical Characteristics Comparison of Virtual Wedge Device With Physical Wedge
Dong Rak Choi, Kyung Hwan Shin, Kyu Chan Lee, Dae Yong Kim, Yong Chan Ahn, Do Hoon Lim, Moon Kyung Kim, Seung Jag Huh
Department of Radiation Oncology, Samsung Medicine Center, College of Medicine, Sungkyunkwan University,Seoul, Korea.
ABSTRACT
PURPOSE:
We have compared the characteristics of Siemens virtual wedge device with physical wedges for clinical application.
MATERIALS AND METHODS:
We investigated the characteristics and physical wedges for various wedge angles (15,30,45,and 60 degrees)using 6- and 15MV photon beams. Wedge factors were measured in water using an ion chamber for various field sizes and depths. In case of virtual wedge device, as upper jaw moves during irradiation, wedge angles were estimated by accumulated doses. These measurements were performed at off-axis points perpendicular to beam central axis in water for a 15Cm x20Cm radiation field size at the depth of 10Cm. Surface doses without and with virtual or physical wedges were measured using a parallel plate ion chamber at surface. Field size was15Cmx20Cm and a polystyrene phantom was used.
RESULT:
For various field sizes, virtual and physical wedge factors were changed by maximum 2.1%and 3.9%, respectively. For various depths, virtual and physical wedge factors were changed by maximum 1.9% and 2.9%, respectively. No major difference was found between the virtual and physical wedge angles and the difference was within 0.5 degrees. Surface dose with physical wedge was reduced by maximum 20% (x-ray beam : 6 MV, Wedge angle: 45 degrees, SSD; 80 Cm) relative to one with virtual wedge or without wedge.
CONCLUSION:
comparison of the characteristics of Siemens virtual wedge device with physical wedges was performed.Depth dependence of virtual wedge factor was smaller than of physical wedge factor. Virtual and physical wedge factors were nearly independent of field size. The accuracy of virtual and physical wedge angles was excellent. Surface dose was found to be reduced using physical wedge.
Key Words: Virtual wedge, Physical wedge, Wedge factor
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