Characteristics of wedge factor of an enhanced dynamic wedge on Varian 600C accelerator
- VernacularTitle:瓦里安加速器扩充型动态楔形板楔形因子特性研究
- Author:
Liang CHEN
;
Yumin LI
;
Hong XU
- Publication Type:Journal Article
- Keywords:
Wedge factor;
Jaw;
Accelerator
- From:
Chinese Journal of Radiation Oncology
1992;0(01):-
- CountryChina
- Language:Chinese
-
Abstract:
ObjectiveTo study the characteristics of wedge factor of enhanced dynamic wedge (EDW) on Varian 600C linear accelerator . MethodsEnhanced dynamic wedge factors (EDWFs) of different jaw settings were measured on a Varian 600C linear accelerator with FARMER 2570 dosimeter and 2571 0.6 ml Thimble ion chamber. At the same time,equations were used to compute EDWFs of symmetric and asymmetric fields and off axis points. The same measurements were carried out on 30 degree physical wedge in contrast to EDW. The accelerator's jaw position was described according to IEC radiotherapy equipment coordinate standard. Results The EDWFs of symmetric field decreased smoothly while the field size increased. Under the same field,EDWFs decreased as the wedge angle increased and the increasing extent became apparent when the field became larger. In off axis fields formed by the upper independent jaws,only the EDWFs of 60 degree had the tendency to increase when the field center moved toward the toe of the wedge,the rest gave the opposite results. The EDWFs of fixed points varied only by 0.5 percent when the fixed jaw remained at the same place and the moving jaw and lower jaws stayed at different positions. But the WF of 30 degree physical wedge increased by 2.9 percent when the lower jaw settings increased from 4 cm to 40 cm. The EDWFs derived from analytic equations for symmetric and asymmetric fields coincided well with measured results. But at off-axis points,the differences between calculated values and measured data were apparent. ConclusionsThe curve of EDWF versus field size is very smooth. The EDWF of fixed point only depends on the position of the stationary upper jaw,and is affected little by the moving upper jaw and lower jaws. The EDWFs of off axis fields are much more complex than those of physical wedge; it shouldn't be confused in clinical application. The conversion method of rectangular field to square field is of no use when EDW field is confronted. Analytic methods are highly conformal with the calculation of EDWFs of symmetric and asymmetric fields.
