What is an AMU?

I've been reading "Radiobiology for the Radiologist" by Eric Hall for the past week or two.  I'm learning a lot from it, but a lot of the cancer terminology is unfamiliar to me.  I'd stop to look everything up, except this book is from the Lane Medical library and I'll need to return it before I leave for WIPP on August 24th.  Since I'm on page 106 of 518, I figure I don't have too much time for backreading.

I decided to simply read the glossary - only a few pages, but should give me almost all of the terminology I need.  Not only are there lots of medical terms, but there is also a lot of physics terms.  I was very confused to see the atomic mass unit (amu) defined as "one sixteenth the mass of a neutral  atom of the most abundant isotope of oxygen, 16O." Oxygen?  The amu I know and love is defined by Carbon!


I check out good ol' wikipedia which clarifies that the "old" amu is, in fact different:

Before 1961, separate conventions were used in chemistry and physics – the physical atomic mass unit (amu) was defined as ¹⁄₁₆ of the mass of one atom of oxygen-16, while the chemical atomic mass unit (amu) was defined as ¹⁄₁₆ of the average mass of an oxygen atom (taking the natural abundance of the different oxygen isotopes into account). Both units are slightly smaller than the unified atomic mass unit, which was adopted by the International Union of Pure and Applied Physics in 1960 and by the International Union of Pure and Applied Chemistry in 1961. Hence, before 1961 physicists as well as chemists used the symbol amu for their respective (and slightly different) atomic mass units. One still sometimes finds this usage in the scientific literature today. However, the accepted standard is now the unified atomic mass unit (symbol u), with: 1 u = 1.000 317 9 amu (physical scale) = 1.000 043 amu (chemical scale). Since 1961, by definition the unified atomic mass unit is equal to one-twelfth of the mass of a carbon-12 atom.

Now, I'm technically reading the 5th edition of this book, which is from 2000.  But the first edition was from 1972... So I'm left wondering if dear Prof. Hall never got the memo that the definition had changed since his education, or if medical physicists really do use units that the rest of physical science has moved on from.