Important Facts!!! Not a question! (Pg. 221)
- An effective depth can be used for calculating transmission through non-water-equivalent materials.
- Close to the boundary or interface, the distriubtion is more complex. For example, for megavoltage beams, there may be loss of electronic equilibrium close to the boundaries of low-density materials or air cavities.
- For orthovoltage and superficial x-rays, the major problem is the bone. Absorbed dose within the bone or in the immediate vicinity of it may be several times higher than the dose in the soft tissue in the absence of bone. This increased energy absorption is caused by the increase in the electron fluence arising from the photoelectric absorption in the mineral contents of the bone.