Description

PREFACE

Since the publication of the Third Edition of The Physics of Radiology,

various international organizations have attempted to introduce SI (sys-
teme international) units into their fields. Of particular interest to us

are the new terms that have been defined for the radiological sciences:

the gray has replaced the rad as the unit of absorbed dose, and the bec-
querel has replaced the curie as the unit of activity.

We are convinced of the advantages of SI and the new units are used
throughout the book. We realize, however, that it will take some time
before workers in the field are at ease with them and for this reason the
older units are often used in parallel with the new ones.
Committees of the I.C.R.U. are attempting to deemphasize the use
of the roentgen as a unit of exposure. In spite of this we have continued
to use it, especially in diagnostic radiology. When patients are exposed
to soft x rays, as they are in diagnostic radiology, there is no single factor
which allows one to go from exposure to dose. The authors feel that the
I.C.R.U. has not adequately assessed the impact of their decision on this
subject. Because the roentgen remains a practical unit, the chapter on
diagnostic radiology still makes extensive use of it.
The use of small electronic calculators has relieved the scientist of

many of the boring arithmetical tasks of the past. We believe that all sci-
entists now use calculators, and we have felt at greater liberty to do calcu-
lations that involve logarithms or exponentials, a procedure which was

previously more difficult. In addition, we have introduced, in the first
chapter, exponential growth and decay, since it is common to all aspects
of radiation and since, for example, we believe the doubling time for the
growth of cells is no more complicated a concept than the determination

of the doubling time of invested money, a topic which everyone under-
stands.

The emphasis in radiation therapy has shifted further towards the use
of high energy beams. We therefore give less attention