Palta J R, Daftari I, Suntharalingam N
Thomas Jefferson University Hospital, Bodine Center for Cancer Treatment, Philadelphia, Pennsylvania 19107.
Med Phys. 1988 Jul-Aug;15(4):624-6. doi: 10.1118/1.596217.
The radiation output in the presence of wedge filters is characterized by the wedge transmission factor and open beam field size factors. Conventionally, the wedge factor for high-energy photons is measured in a water phantom at depth of maximum dose for a reference field size. Experimental measurements on different wedges indicate that the wedge factors are a function of field size. An analysis of these data show that this is primarily caused by the change in scattered radiation from the treatment head in the presence of wedge filters. The change in phantom scatter and radiation backscattered to the monitor chamber are minimal. For 4- or 6-MV x rays with a 60 degrees wedge, the use of a single wedge factor measured for 10 cm X 10 cm field introduces errors of up to 3.5%, for a 16-cm-wide field. For a 20-cm-wide field with this wedge, the error is 7%. Thinner wedges exhibit less differences.
楔形滤过器存在时的辐射输出由楔形滤过器透射因子和开放射野尺寸因子来表征。传统上，高能光子的楔形因子是在水模体中针对参考射野尺寸，在最大剂量深度处测量的。对不同楔形滤过器的实验测量表明，楔形因子是射野尺寸的函数。对这些数据的分析表明，这主要是由于在楔形滤过器存在的情况下，治疗头散射辐射的变化所致。模体散射和反向散射到监测电离室的辐射变化很小。对于带有60度楔形滤过器的4兆伏或6兆伏X射线，对于16厘米宽的射野，使用针对10厘米×10厘米射野测量的单个楔形因子会引入高达3.5%的误差。对于使用这种楔形滤过器的20厘米宽射野，误差为7%。较薄的楔形滤过器差异较小。
