In radiotherapy, wedges are commonly used as beam modifier to improve the dose coverage to the target and to reduce hotspots as well. In the case of enhanced dynamic wedge, the required dose distribution can be achieved by one of the collimator jaws motion in two directions ( IN and OUT).Wedge filters can also be used as missing tissue compensators or wedge pairs to alter the shape of isodose curves so that two beams can be angled with small hinge angle at target volume without creating any hotspot.The wedge angle refers to the angle through which the isodose curves are tilted, relative to their normal position perpendicular to the beam axis at reference depth. The international commission on radiation units and measurements (ICRU) recommendation for reference depth is 10cm. The presence of wedge filter in the beam path reduces the beam intensity and this must be taken into account during treatment planning. It is generally assumed that for wedged fields of different size, a single wedge factor must be measured for a reference field size, is valid for calculation. Plta et al. has already examined field size dependency of a wedge factor using the Varian Clinac-4 wedge filters and Philipâ€™s SL75/5 auto wedge . The Physical wedges (PW) have been the primarily means of producing the wedged fields. The required wedged dose profiles can also be achieved by computer control motion of one of the jaws. Such type of wedge is called dynamic wedge, which was first introduced by Varian medical system in early 1990s in linear accelerator.The dynamic wedge can provide angles of 15Â°,30Â°,45Â°, and 60Â° only for symmetrical field size up to 20cm width. The ability of dynamic wedge are significantly improved by introducing the concept of Varianâ€™s enhanced dynamic wedge ( EDW). Now the EDW provides wedge angle of 10Â°,15Â°,20Â°,25Â°,30Â°,45Â°, and 60Â° for both symmetrical and asymmetrical field sizes up to 30cm width. A number of studies have been conducted on PW and EDW [7-9]. However, so far studies related to comparison of Varianâ€™s PW and EDW has not been reported [10-13].The effect of enhanced dynamic wedge factors (EDWF) for symmetrical and asymmetrical photon fields have been discussed in many literatures [14-16].
In future, Physical wedge will be totally out of use. It is, therefore, need to understand the physics and dosimetric impact of EDW in radiotherapy plan.
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