How does bolus material impact the treatment surface dose compared to custom compensators?

Bolus material is utilized in radiation therapy to enhance the surface dose delivered to the treatment area. When bolus is placed on the skin, it effectively brings the dose distribution closer to the surface, ensuring that more radiation is deposited at or near the skin level. This is particularly useful in situations where tumors are located just beneath the surface or in cases where a high surface dose is required to treat the disease effectively.

The physical characteristics of bolus, such as its density and thickness, play a significant role in modulating how the radiation interacts with the tissue. By absorbing and scattering the radiation, bolus not only increases the dose delivered at the skin's surface but also helps in equalizing the dose across irregular surfaces of the body where a uniform dose distribution is necessary.

In contrast, custom compensators serve a different purpose. They are designed to modify the dose distribution based on the patient's anatomy and treatment plan, often accounting for tissue inhomogeneities. However, while compensators may have an indirect effect on surface dose, their primary aim is to create a uniform dose distribution rather than specifically increasing the surface dose.

Thus, bolus material distinctly increases the surface dose, making it the correct answer in this scenario.