In 2011 we treated Arlie with Pamidronate, then the biophosphonate of choice, and palliative radiation. Her tumour was in her left rear leg. She responded very quickly to the radiation and other than being very tired the next day, didn't seem to experience any side effects. She was also on oral pain meds, but with that combination seemed to feel really well. However, as tbhounds points out, radiation in any form doesn't address weakening of the bone due to cancer, and indeed, a couple months in Arlie tripped and fractured the leg. As factures go it could have been a lot worse (it was a green stick fracture) but there was nothing that could be done for her and we let her go. In some jurisdictions (unfortunately not ours) your oncologist can dispense a morphine or similar syringe, so that if this happens you can address the pain quickly and give some relief until you can get your dog in to the vet or the emerg. I am so sorry you are facing this.