A beam flattening filter is used with which type of beam?

A beam flattening filter (BFF) is specifically designed for use with photon beams. The primary purpose of this filter is to modify the intensity profile of the radiation beam so that it becomes more uniform across a treatment field. In radiation therapy, when a photon beam is generated, it often has an uneven intensity distribution, which can lead to areas of over-treatment or under-treatment within the target area.

The beam flattening filter is strategically placed in the path of the photon beam. It effectively attenuates the central, more intense part of the beam while allowing the peripheral regions to be less attenuated. This results in a uniform dose distribution, which is critical for ensuring that the intended volume of tissue (tumor) receives the prescribed dose while minimizing exposure to surrounding healthy tissues.

In contrast, electron beams do not require flattening filters because their spatial energy distribution is naturally more uniform. Other types of beams such as X-ray and gamma-ray beams can have other methods of beam shaping or do not typically utilize a beam flattening filter in therapeutic contexts. Therefore, the correct association of beam flattening filters is specifically with photon beams in radiation therapy practices.