Activity, which is a way in which the strength of a brachytherapy source can be specified, can be specified in terms of mCi and the exposure rate at any particular point is proportional to the product of activity and its exposure rate constant. What are some corrections that would need to be done to the approximated activity value? Pg. 321
Errors, however, may be introduced in this method from the fact that corrections must be applied for the source and wall filtration and that the exposure rate constant may not be known accurately. It should be recalled that the accuracy of the exposure rate constant depends critically on the accurate knowledge of the spectroscopic data and the relevant absorption coefficients.