back up phots from icloud to pc en masse without using itunes

If you're talking about a few dozen photos or maybe even a few hundred, I'd say visit iCloud.com and sign in with your Apple ID. You could try it with a larger number but I'd imagine there's a limit somewhere!

If you want to download a vast quantity of photos from iCloud to your PC, it's probably better to install iCloud for Windows.

For more information, see Archive or make copies of the information you store in iCloud.