While prostate surgery
makes it impossible to father children without heroic medical intervention, prostate radiation
merely makes it difficult. I did a bit of Googling to see if I could find an actual answer to your question and, of course, I couldn't. I did find this recent article that comes close to addressing your question but not, actually, closer than my "difficult but not impossible" observation above.Recovery of Spermatogenesis Following Cancer Treatment with Cytotoxic Chemotherapy and Radiotherapy
It does mention that fractionalization makes the damage to the testes worse so your hypofractionalized SBRT radiation should have less of an effect on your fertility than would normal IMRT. It talks about
radiation doses and fertility but it is mostly discussing radiation dose directly to the testes so you'd have to ask your RO how much scattered dose he thinks the testes would have received.
But the bottom line is that as far as the effect of the radiation on your ability to father a child there is no way to know for sure one way or the other.