What type of filters are used to manage varying thickness in radiotherapy?

Wedge filters are specifically designed for use in radiotherapy to manage varying thickness in tissue. The primary purpose of these filters is to create a more uniform dose distribution across a treatment area where the thickness of the tissue may vary. By inserting a wedge filter, radiation is preferentially attenuated, allowing for a higher dose to be delivered to thicker areas while reducing exposure to thinner areas. This helps to ensure that the intended target volume receives an adequate dose, improving treatment effectiveness while minimizing damage to surrounding healthy tissue.

In contrast, other choices do not serve the same function in managing tissue thickness. Composite filters are used for different applications and do not specifically address variable thickness. Grids are used to reduce scatter radiation and improve image quality rather than for dose distribution in treatment planning. Phase filters, while relevant in certain contexts, are not commonly referenced in the management of thickness in radiotherapy. Therefore, the use of wedge filters is the most appropriate answer to address the challenge of varying thickness in radiotherapy.