Which device is used in radiation oncology to modify the treatment beam?

In radiation oncology, a wedge is a specialized device used to modify the treatment beam during radiation therapy. The primary function of the wedge is to create a gradual change in the dose distribution across the treatment area. This is particularly important when treating irregularly shaped tumors or when specific parts of healthy tissue need to receive a lower dose of radiation, while ensuring adequate coverage of the cancerous tissue.

Wedges are designed to attenuate the radiation dose on one side more than the other, allowing clinicians to effectively manipulate the dose gradient. This ability to customize the beam shape and intensity helps in maximizing the treatment efficacy while minimizing the exposure to surrounding healthy tissues.

While other devices, like filters, collimators, and shields, serve important roles in radiation therapy, they do not quite match the specific functionality and purpose of a wedge in beam modification. Filters are used to alter the energy spectrum of the beam, collimators shape and direct the beam, and shields are primarily used to protect areas of the body from radiation exposure rather than modifying the treatment beam itself. Thus, the wedge stands out as the correct choice for its unique role in beam modification in radiation oncology.