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Dosimetric aspects of physical and dynamic wedge of Clinac 2100C linear accelerator
J S Avadhani1, A S Pradhan, A Sankar
1Department of Medical Physics, Tata Memorial Hospital, Mumbai, India.
Aim:
To investigate variation of wedge factors on field size and depth for physical and dynamic wedges of identical wedge angles for Clinac 2100C linear accelerator and its clinical implementation.
Material And Methods:
A computer controlled water phantom dosimetric system is used to generate profile data for physical wedges, whereas a 0.6 cm3 ion chamber is used for generation of profiles for dynamic wedge and wedge factors for both types of wedges. The method has been discussed to handle the dynamic wedge dosimetry in absence of linear array of detectors or film densitometer.
Results:
A systematic dependence on wedge factor is observed for physical wedge, with respect to depth and wedge angle but not depending on field size. Whereas dynamic wedge shows strong dependence on field size and is not systematic because the dynamic wedge is controlled by segmented treatment tables depending on field size and energy and no significant variation is observed on depth for various wedge angles. The handling of beam data in a commercially available treatment planning system is discussed and a comparison has been made for iso-doses of both types of wedges.
Conclusion:
The dynamic wedge isodose curves shows rather straight lines than physical wedge but larger hot spots at thin edge which needs careful consideration during planning.