How does the filtration of the x ray beam protect the patient?

Filtration is the process of increasing the mean energy of the x-ray beam by passing it through an absorber. The primary x-ray beam is polychromatic, that is, the beam contains a spectrum of photons of different energies and the average energy is one-half to one-third of the peak energy. Many of the photons produced are low energy and, if they escape through the glass window of the tube, they are absorbed by the first few centimeters of tissue and contribute nothing to the exposure of the film. Only the higher energy photons can penetrate the patient and reach the film to assist in making the radiograph The dose of radiation received by the patient is highest in the first few centimeters of tissue because of absorption of this low energy portion of the x-ray beam. The amount of scattered radiation is higher with an unfiltered beam because of the number of low energy photons. So, it is advantageous to both the patient and to the technician to use a filtered x-ray beam.