It used to be done as two fractions, 2 weeks apart, as in that thread.
Mount Vernon now do it as two fractions a day apart, so you stay in hospital overnight, rather than coming back 2 weeks later.
(Actually, if you go back 8+ years, it was usually 4 fractions, but I doubt anywhere does it like that any more.)
I had a single HDR fraction, but that was combined with external beam radiotherapy (HDR Boost).