This seems to be a symptom of a problem with many causes, but this is what worked for me.
I didn't want to rebuild my library from scratch (in my present user, or in a new Windows user) because of the time involved. I tried other suggestions here:
1. Start iTuners with Shift+Control. That allowed me to run iTunes at about one in 7 attempts, but it wasn't a real solution.
2. I tried reinstalling both iTunes and Quicktime, of course. No improvement.
3. I tried moving C:\Users\username\AppData\Local\Apple Computer\iTunes and C:\Users\username\AppData\Roaming\Apple Computer\iTunes away from their usual place. iTunes made a new copy and I had to re-select some personal settings, but no improvement.
4. Tried turning off automatic refresh of podcasts.
I'm running Windows 7 64-bit fully up to date. On the last update (to 11.4.0.18), I noticed that Apple was offering me the 32-bit version of iTunes, despite having 64-bit Windows, I have had solid performance for several days now with the following actions:
1. Uninstalled iTunes and Quicktime.
2. Downloaded and installed the *64-bit* version of iTunes (called iTunes64Setup.exe at the time of writing). Actually, even with that, most of iTunes still goes in C:\Program Files (x86)\iTunes but there is a folder and 3 dlls in C:\Program Files\iTunes and some files in C:\Program Files\iPod
Now, I don't get abnormal closes with iTunes.