ABSTRACT
One common case utilizing the concept of the geometry factor is the calculation of the dose rate in an organ from a radioisotope deposited in that organ. For example, what is the dose rate to the thyroid from radioactive iodine given to a patient? If the organ is further assumed to be spherical, Eq. 16.23 takes the simple form
µ
= = −∫ 2 20 e 44 d (1 e ) rR Rg r r
r (16.24)
Using this value of g with Eq. 16.22 gives the dose rate at the center of the sphere. To obtain the average dose rate, an average value of g should be used. For a sphere the average value of the geometry factor is (see Cember, 2008)
= center0.75 ( )g g (16.25)
Average geometry factors for cylindrical bodies are given in Table 16.5. An example of using geometry factors is given in Section 16.6.
