What happens to the skin dose when an electron beam is incident obliquely compared to normal incidence?

When an electron beam is incident obliquely rather than at normal incidence, the skin dose increases. This occurs because oblique incidence affects the path length of the electrons in the tissue. As electrons enter the skin at an angle, the effective distance they travel through the tissue before they scatter and lose energy is reduced compared to a direct, perpendicular entry.

In an oblique configuration, the electrons have a longer path within the tissue where they can scatter back towards the surface, thereby enhancing the dose delivered to the skin. This effect is particularly pronounced because electrons are low-energy particles and are significantly influenced by tissue interactions. The increase in dose to the skin can also be attributed to the altered geometry of the beam and the scattered electrons that are more likely to contribute to the dose at the surface in oblique incidence scenarios.

Understanding this relationship between beam incidence angle and skin dose is crucial in dosimetry practice, as it directly impacts treatment planning and the protection of healthy tissues during radiation therapy.