Andrew,. The incidence of secondary cancers following RT is not "very uncommon". There is a great reluctance on the part of oncologists to accept that subsequent bladder cancer (which both my late brother and I got within five years if having RT) and bowel cancer is related to poorly aimed RT. I am very doubtful about the collection of statistics on this, therefore.
I'm sure that modern methods are a great improvement on what was done ten years or more ago, but all who had RT in those early days should be watchful for the signs suggesting a problem.
AC