Question

How Kerma and Absorbed dose can be calculated and measured?

Answer 1

Answers:-..

The purpose of the paper is to clarify the conditions under which absorbed dose can be determined from a measurement of exposure.

It is shown that, for megavoltage photons, the equation D=fX, relating the absorbed dose to the exposure at a point, is valid on the central axis of the field only at the point where the kerma curve, K(z) vs. depth z, crosses the absorbed dose curve, D(z) vs.

. This point is expected to be at a depth slightly less than the depth of peak absorbed dose.

At depths where the absorbed dose curve becomes exponential, it is shown that D = {β/(β−μ)}fX, where μ is the effective linear attenuation coefficient for the photons, and β is the effective linear energy absorption coefficient for the secondary electrons.

. Alternatively, D(z) = f{(F+z−δ)/(F+z)}2 X(z−δ), where D(z) is the absorbed dose at depth z and X(z−δ) is the exposure at depth (z−δ). The equation for δ as a function of μ and β is derived and approximate values of these constants are given for different megavoltage radiations.