Percentage Depth Dose
medradiation | يكشنبه, ۸ شهریور ۱۳۹۴، ۱۰:۵۵ ق.ظ
Percentage Depth Dose
One way of characterizing the central axis dose distribution is to normalize dose at depth with respect to dose at a reference depth. The quantity percentage (or simply percent) depth dose may be defined as the quotient, expressed as a percentage, of the absorbed dose at any depth d to the absorbed dose at a fixed reference depth d0, along the central axis of the beam (Fig. 1). Percentage
One way of characterizing the central axis dose distribution is to normalize dose at depth with respect to dose at a reference depth. The quantity percentage (or simply percent) depth dose may be defined as the quotient, expressed as a percentage, of the absorbed dose at any depth d to the absorbed dose at a fixed reference depth d0, along the central axis of the beam (Fig. 1). Percentage
Figure 1: Percentage depth dose is (Dd/Dd0), where d is any depth and d0 is reference depth of maximum dose.
For orthovoltage (up to about 400 kVp) and lower-energy x-rays, the reference depth is usually the surface (d0 = 0). For higher energies, the reference depth is taken at the position of the peak absorbed dose (d0 =dm).
In clinical practice, the peak absorbed dose on the central axis is sometimes called the maximum dose, the dose maximum, the given dose, or simply the Dmax. Thus:
A number of
parameters affect the central axis depth dose distribution. These include beam
quality or energy, depth, field size and shape, source to surface distance, and
beam collimation.
