The dose perturbation caused behind any inhomogeneity primarily depends on which of the following factors?

The dose perturbation caused behind any inhomogeneity is primarily influenced by the electron density of the materials present. When radiation passes through different materials, varying electron densities can significantly alter how the radiation interacts with matter, affecting how much energy is deposited in tissues behind the inhomogeneity.

Inhomogeneities such as air cavities, bones, or soft tissue will have different electron densities, leading to changes in scattering and attenuation of the radiation. High electron density materials, like bone, will scatter and absorb more radiation compared to low electron density materials, like air. This variation in electron density is crucial because it plays a critical role in dose calculations and treatment planning, ensuring that the intended dose is accurately delivered to the target area while minimizing exposure to surrounding healthy tissues.

Shape and size of the inhomogeneity do play roles in dose distribution, but the primary factor that determines the extent of the perturbation in dose delivery is the electron density of the materials involved. The effective atomic number can also affect the interactions to some extent, but it essentially correlates with electron density and is not the primary determinant for dose perturbation. Understanding electron density is fundamental for medical dosimetrists in refining treatment plans to achieve optimal therapeutic outcomes while mitigating risks.