Not an option, at 70+, you are near certain to end up impotent, and probably in nappies as well. While radiotherapy present similar risks but the side effects are delayed, and blunt incontinence is unlikely. There is also the risk of rectal damage but this now mitigated by the "Space OAR" hydrogel rectal spacer.
SBRT is become quite popular as the whole treatment can be carried out in 2 to 3 weeks, while IMRT/IGRT can last up to 6 or 7 weeks.