Select the true statement regarding bolus materials in radiation therapy.

Bolus materials play a crucial role in radiation therapy, especially when treating surface tumors or lesions. The true statement regarding bolus materials is that they help to deliver a uniform dose to the skin surface. This is because bolus materials are used to modulate the radiation beam, ensuring that the maximum dose of radiation is deposited at or near the surface of the skin, where certain tumors may be located. The use of bolus ensures that the radiation dose is homogeneous across the target area, preventing hot spots or cold spots that could occur due to variations in tissue density.

Using bolus enhances the effectiveness of the treatment by allowing clinicians to compensate for the lack of dose buildup at low-energy photon beam treatments. Additionally, bolus materials are typically designed to closely mimic the scattering properties of human tissue, further improving dose distribution.

The other options highlight misconceptions about bolus materials. They are not exclusively made of water, as they can be composed of various materials such as gel, rubber, or other tissue-equivalent substances. They can be used with both photon and electron beams, not just photon beams. Finally, bolus materials do play a significant role in treatment planning, particularly in treatment scenarios that require precise dose profiles at the skin surface, so they are