What is the PSF for a 60Co beam under the same conditions?

In medical physics, the Percentage Surface Dose (PSD) is a key parameter in treatment planning that quantifies how much of the delivered dose is received at the surface of the tissue being treated. The Physical Skin Dose Factor (PSF) refers to the ratio of the dose at a specific depth (usually at the surface or close to it) to the dose that would be delivered at the same point if there were no intervening materials or if it were in a vacuum.

For a 60Co beam, which generates gamma radiation, the PSF is influenced by several factors including energy, beam quality, and other geometric and physical properties. In this case, the PSF value of 1.05 indicates that the dose delivered at the surface when using a 60Co source is slightly higher than the baseline case for a medium (often taken as water).

This value can be attributed to the characteristics of cobalt-60 radiation. The gamma rays produced have a specific energy profile which leads to a higher surface dose due to the build-up effects. At lower energies, such as those produced by 60Co, there's a notable increase in the dose delivered at the surface compared to deeper layers because lower-energy photons are more likely to be absorbed or scattered near